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What It Is?...

(c.a., December 2007)

Over time my various pages have been getting longer and longer, (not a bad thing). But, some are filling up with construction details and related information that is applicable to much more than just their specific project. For a couple of pages the situation is reaching a point where weaving real project information through generic technique descriptions so that everything flows in a logical manner without losing more salient details in a textual forest is becoming increasingly difficult. In fact, that is one of the main reasons why though I have been working on a number of my projects fairly diligently for the last year, I haven't been doing any major updates to my pages.

So, to get things back up to date, and to help keep project pages essentially project related, I'll be putting the more heavy-weight and generic construction information into independent detail sections on this page. Those independent sections will be referred to from the main project pages. Hopefully having miscellaneous details separated from the main project text will make my pages a little easier to follow, as well as easier to keep current.


One Ring To Rule Them All:

(c.a., December 2006)

The Mark-II turbine volute was formed by heating and bending a flat 2.5" wide, 0.091" thick, approximately 38" long acrylic plastic strip into a ring. The plastic strip was bent around a turned, laminated wood form 2.75" thick with an 11.75" outside diameter. The turned ring was screwed onto a 12.5" square piece of 0.5" thick plywood; providing a base to align an edge of the plastic strip against as the strip was bent. This section details constructing the volute forming ring, and preliminary acrylic ring bending tests.

Square It:

An 11.75" square, 2.75" thick wooden blank for turning on a lathe into the volute forming ring was built up by laminating 1"x4" pine boards into horizontal sheets, then laminating these sheets vertically. The boards were planed to the same thickness, and edges squared on a woodworking jointer. Since these were rough cut boards of varying thickness, they were not planed so that each layer in the vertical lamination was the same thickness. Rather, single boards of length sufficient to provide all the material for a single layer were chosen and individually planed to a uniform thickness. Thus the lamination vertical build up was level, even though the horizontal layers have different thicknesses.

[ring flat] [ring flat]

Boards forming layers in the lamination stack were laid at 45° to boards in the layer below. Prior to gluing, boards in the stack were marked with a pencil to give cut off lines providing a roughly square lamination. To simplify the build up process, a piece of 0.5" thick plywood was used as the first lamination layer.

[ring flat] [ring flat] [ring flat] [ring flat] [ring flat]

The lamination layers were glued up one at a time, clamping them between pieces of 0.5" thick plywood while the glue hardened. After applying glue and clamping, each layer was given a few wacks with a dead blow hammer to ensure a tight fit between the boards. (Making sure to hammer from the corner on 45° cut layers, so not to slide the boards lengthwise.)

[ring flat] [ring flat] [ring flat]

Once the lamination process was complete, the roughly square blank was cut to be square on a table saw. Then lines were draw corner-to-corner to mark the blank center point, and a few lines were drawn parallel to one of the corner-to-corner lines for alignment aids after the blank is turned round. A 0.5" diameter hole was drilled at the center of the blank to insert a rod for mounting the blank into the lathe chuck.

[square up] [square up] [square up] [square up] [square up]

Spin It:

A 0.5" rod slipped through the 0.5" hole in the wooden blank and clamped into a lathe chuck would give proper alignment for turning the blank. But, turning the blank would still be impossible without some means of fixing the blank to the rod. A simple way to make a spinning fixture is to use threaded rod, a coupling (long) nut appropriate for the rod thread, and a floor bracket (used for mounting threaded pipe to a floor or wall) with a center hole slightly larger than the diameter of the threaded rod. Chuck a length of threaded rod into a drill press, screw the coupling nut onto the end of the rod, then place the floor bracket on the drill press table and lower the coupling nut into the center hole of the bracket. This way the flat side of the floor bracket is unavoidably perpendicular to the threaded rod. Make a couple of tack welds of the nut to the bracket to fix things in place, then remove the rod from the drill press and off to some place to do a proper weld job without splattering all over your drill press table. (If your bracket is galvanized, it would be a good idea to buff the galvanizing off the area to be welded with a wire wheel first.) Once the weld is complete, the bracket can be placed anywhere along the length of the rod by threading the coupling nut to the desired position then double-nutting against it to fix it in place. Slipping the threaded rod through the hole in the blank to be turned, and using wood screws through the bracket mounting holes to fix it to the blank ensures a well aligned and ready to turn assembly. For a heavy blank, backing up the bracket with a washer and nut on the rod through the blank on the opposite side from the floor bracket could be a good idea as well.

NOTE! Cheap threaded rod is not always straight, and the smaller its diameter the worse the problem. For this technique use the largest diameter and shortest length of threaded rod possible. Here, an approximately 10" length of 0.5" US standard-thread rod was used.

[spindle] [spindle] [spindle]

Of course, just because you can mount a square blank in a lathe and turn it round, you shouldn't necessarily do that without hacking of major corner chunks from the blank first. Why spend all day turning off material you can remove with a saw in minutes?

Here, to facilitate the saw work, a paint stirring stick was marked on the center line near its handle end for a 0.5" hole to fit over the 0.5" rod of the spinning fixture described above. Measuring out along the center line of the stirring stick from the center mark for the 0.5" hole mark another mark was made to indicate the radius the blank was to be turned to (5.875"). A 0.1875" hole was drilled at the radius mark for inserting a 0.1875" transfer punch to use as a scribe for marking the blank. With the blank marked using the paint stirrer compass, the majority of material to be removed was cut off using a table saw before mounting the blank on a lathe and turning to its final diameter.

[round off] [round off] [round off] [round off]

With the close fit of the spinning fixture rod in the center hole of the blank, (which was drilled on a drill press), and the planed surfaces of the blank's lamination pieces making the faces of the blank parallel, the rod sits perpendicular to the top of the blank without the welded assembly of the spinning fixture being in place. With the welded assembly spun down the threaded rod to meet the blank face and attached with four 1.5" #10 wood screws, and the opposite blank face backed up with a washer and nut on the other end of the rod, the blank is ready to spin.

[align spindle] [align spindle] [align spindle]

Round It:

With the spinning fixture rod clamped in the lathe chuck, the blank was turned round, and also grooved to allow later removal of the center piece of the ring with a jig saw. The outer surface of the turned ring was finished with a medium grade sandpaper strip.

[turn down] [turn down] [turn down] [turn down]

Using the paint stirrer compass again, remarked and drilled to indicate the center of the groove in the turned blank a line was scribed on the blank face opposite of the groove. After drilling a hole to accept a jig saw blade just inside of the scribe line, a jig saw was used to separate the center section of the blank from the turned ring portion by cutting along the scribed line.

[remove center] [remove center] [remove center] [remove center]

Although not critical to its use, the center of the ring was squared up relative to the top surface using a sanding drum mounted in a hand drill, and a small square.

[align spindle] [align spindle] [align spindle]

Ready It:

With the forming ring prepared the final step to make it ready for use was mounting it to a piece of 0.5" thick plywood slightly larger than the diameter of the ring. This gives an edge to align a plastic strip to as it is heated and bent around the form, thus keeping the final shaped ring square. The remainders of the diagonal hole-centering lines left on the ring after the blank was turned were used to "eyeball" align the ring with corner-to-corner diagonal lines on the plywood piece. This places the ring reasonably close to center of the plywood piece. With the ring clamped in place, four counter-sunk pilot holes were drilled for #10 wood screws used to attach the ring form to the plywood piece. Even though its laminated construction makes it fairly resilient, pilot holes are still a good idea for large screws; making it easier to drive them in and also help prevent splitting the ring. Bee's wax was applied to the screw threads to further ease driving in the screws.

[ring mount] [ring mount] [ring mount] [ring mount]

Strip It:

In theory one should be able to score and snap acrylic sheet plastic to a desired size. In reality, particularly with the cheap hobby-grade plastic used here, I've had limited success with that operation. And, the longer and more narrow the piece of material to be snapped off, the more difficult it becomes. So, rather than even try and fight snapping off a 2.5" wide piece of 0.091" thick material more than three feet long, I set up a cutting fixture with boards and c-clamps, and cut several strips with a jig saw, using a fine-tooth finishing blade.

[cut strip] [cut strip]

Heat It:

Clear acrylic plastic sheet can be heated and bent, and, if heated to the correct temperature, will take the bend and not rebound when cooled. So, properly heating the plastic strip, bending it around the wooden ring and lightly clamping it in place while it cools will create a well-formed ring of plastic having the same inside diameter as the outside diameter of the wooden ring.

I made a preliminary try at bending a ring around the newly turned ring fixture using a heat gun and "feeling" the bend in the acrylic strip. As the bend progressed around the ring, the plastic strip was lightly clamped in place using small wooden blocks and c-clamps. (In fact, I bent two short pieces to from a full ring to see how closely they would align.)

This method worked well enough to demonstrate that even without direct heat control, a little practice would allow one to form high quality rings. But, as can be seen in the photos, it is very easy to move the heat source too close and over heat the plastic, crazing its surface. A method for more precise temperature control is presented in the "Around the Bend" section below.

[bend strip] [bend strip] [bend strip] [bend strip] [bend strip]


Around The Bend:

(c.a., May 2007)

Clear acrylic plastic sheet can be heated and bent, and, if heated to the correct temperature, will take the bend and not rebound when cooled. That is, if properly supported so it doesn't deform under its own weight while in the heat-softened state, the plastic will keep the exact shape of the initial bend once it cools and becomes rigid again. This no-rebound bend temperature is referred to as the forming temperature, and varies for different plastic materials. For cast acrylic plastic sheet of the Plexiglas™/Lexan™ varieties used here, the forming temperature ranges between 320° F to 356° F [1].

For this project, rather than try and create some kind of heater/clamp fixture that would encompass the full surface of the plastic strip and apply heat and force the bend to fit the wooden forming ring in one operation, the forming temperature principle was used so that the plastic strip could be heated in stages and bent to shape with minimal clamping requirements.

Properly heating the plastic strip, bending it around the wooden forming ring and lightly clamping it in place while it cooled created a uniformly curved plastic ring having the same inside diameter as the outside diameter of the wooden ring.

Hot Stuff:

A 1500 W heat gun was used as the basic heat source. I initially thought to create a temperature control circuit to insert into the gun's original heater circuit, did some designs, bought some parts, did some fiddling, then realized that the required temperature sensor would always be at a fixed distance from the heat gun nozzle and thus set the temperature not just at a particular level, but, set it to the chosen temperature level at the distance of the temperature sensor from the heat gun outlet; which lead me to recognize since the heater circuit of the gun itself provides a relatively consistent output, just keeping the gun snout at the distance from the plastic which allows the heated output air stream to cool to the forming temperature is all that is required without invoking any clever electronics. (Well, at least now I have a few more nifty parts in my junk box for future fun.)

The forming-temperature cooling distance was determined using a hose clamp, a length of 0.125" diameter stiff wire, and an oven rack thermometer. The wire rod was bent to fit over and clamped to the heat gun snout so that it extended along the line of the heated output air stream. The oven thermometer was hung on the wire, the heat gun turned on to its highest setting, and, after a few moments wait for the gun to reach full temperature output, the thermometer was slid down the wire until it read the desired forming temperature, in this case approximately 325° F. Once that distance was found, the wire was bent, (using two pair of plyers to avoid any unpleasant sensations), marking the distance, and cut off below the bend.

[heat source] [heat source] [heat source] [heat source] [heat source]

Always working with the bent wire end next to, and the wire perpendicular to, the surface of the plastic strip maintains the forming temperature at the plastic's surface during the bending process.

All The Way 'round:

To bend a plastic strip around the wooden forming ring, a long edge at one end of the strip was laid against the ring's 0.5" thick plywood base plate, and that end clamped to the ring with a small wooden block and a c-clamp. (Note in the photos how the opposite end of the strip was elevated on a separate block of 0.5" thick wood to prevent any twisting of the strip during the bending process.) Then, starting at the clamped end, the strip was heated to its forming temperature using the "calibrated" heat gun along about 10 inches of its length and the softened plastic pulled against the forming ring, taking the curve of the ring. With the strip pulled against the form another wooden block and c-clamp set was used to lightly clamp the strip to the form about an inch inside the end of the heated zone farthest from the clamped end of the strip. This process was repeated staring at the last block and clamp set, continuing all the way around the form. Since the plastic was bent using its forming temperature, it was possible to simply "leap frog" wooden block and c-clamp sets around the forming ring without compromising the curve, once each heated zone cooled enough to regain rigidity.

[bend ring] [bend ring] [bend ring]

Once the process of heating and bending the strip to fit the form reached back around to the beginning, the starting end was pulled back, and the finishing end, (which extends past the starting end), was heated and bent to fit the form directly. When the finishing end cooled, the starting end was released to spring down and overlap the finishing end due to its already having been bent to fit the ring. This last step in bending the strip around the forming ring allowed the ends of the strip to be trimmed close and the volute ring to be sealed.

In Closing:

With both ends of the acrylic plastic strip bent to the curve of the forming ring, and let overlap, sawing through the overlapping material and removing the excess pieces leaves a gap one saw-kerf wide which can be glue filled to seal and complete the volute ring. The set up for this operation was to clamp the forming ring base board vertically in a vice, cut a notch in the base board to allow a thin-bladed hacksaw to cut into the overlapping plastic strip ends across the full face of the wooden forming ring, then clamp the previously heated and bent plastic strip in place on the ring form.

[close ring] [close ring]

With the overlap cut through and the excess pieces cleaned out, a piece of waxed paper was placed under the saw-kerf gap, the gap filled with 5-minute epoxy, another piece of waxed paper laid over the gap and a small block of wood clamped over that to hold the gap edges in place until the glue hardened. Once the glue was dry, the clamps were released, the plastic ring pulled off the forming ring, and the waxed paper peeled away, leaving the finished product, a well-formed acrylic plastic ring suitable for use as the Mark-II turbine volute.

[close ring] [close ring] [close ring] [close ring] [close ring]


On The Side:

(c.a., May 2007)

After the basic volute ring was formed, two acrylic plastic rings were turned from 0.236" thick material to have the same inside diameter as the outside diameter of the volute ring, and an outside diameter approximately 2.5 inches greater than that. One of these rings was mounted using high-strength epoxy glue on each edge of the volute ring to provide rigidity to the volute and also allow mounting of 0.236" thick material turbine side plates, (one of which slips inside the volute to allow adjusting the usable inside width of the volute). The details of this construction are provided in the text subsections below.

Roughly Speaking:

A table saw was used to cut rough octagonal blanks from 0.236" thick acrylic plastic sheet for the Mark-II turbine volute stiffening rings and side plates.

Yes, you can cut acrylic sheet on a table saw. It isn't necessarily the best method, but it is fast. A plastic-cutting saw blade is highly recommended! Even then, be prepared for a shower of hot plastic bits. If you only have a standard blade, be prepared for a heavy shower of hot plastic bits. But, you always wear eye protection when using power tools anyway, RIGHT?!!

[parts is parts] [parts is parts]

After the blanks were cut, 0.5" center holes were drilled in them to facilitate their mounting in an alignment jig. Acrylic plastic is brittle, unless it gets warm, then it is gummy. Both these states are problematic when drilling holes. You should always clamp the material when drilling to help keep it from climbing up your drill bit when it breaks though the reverse side of the piece. Also, stepping up through several successively larger drill bits will help prevent cracking when drilling large holes. Particularly for thin material, backing up with wood to drill into, rather than just breaking out into the air will also help prevent cracking. Standard taper bits will work just fine, but, keeping them sharp should go without saying. A little water for lubrication and cooling can help, too.

[parts is parts]

Mount Up:

A combined alignment and turning jig was constructed from a piece of 0.75" plywood, cut to the same basic octagonal shape and size as the acrylic plastic stiffening ring and side plate blanks, and center drilled with a 0.5" hole. The hole permits the rod from the turning fixture used in constructing the volute forming ring to pass through the jig so it can be use to mount the jig in a lathe. The floor bracket of the turning fixture is screwed onto the back of the alignment jig using #10 wood screws, with pilot holes drilled and a bit of bee's wax applied to ease their insertion and removal. The bracket is spaced off the jig board with a 0.5" thick hardwood block to prevent the screws from poking out through the face of the jig.

[main jig] [main jig] [main jig] [main jig]

With the turning fixture rod extending through the face of the alignment jig, the paint stirrer compass could be used. A circle with radius from jig-center to a point half-way between the outer diameter of the volute ring and the outer diameter of the stiffening rings was scribed on the face of the jig. Referencing the marks used to drill the jig center hole, a large 30-60-90 drafting triangle was used to put marks on the scribed circle line at equally spaced 60° intervals. The marked positions were center punched, then close fit holes for 6-32 threaded screws were drilled at each of the punched positions, using a drill press to insure each hole's perpendicularity to the alignment jig face. Long 6-32 thread screws inserted through these holes were used for various alignment tasks during construction of the Mark-II turbine.

[main jig] [main jig] [main jig] [main jig]

The alignment jig was used to drill holes at 60° intervals around the stiffening ring and side plate blanks by first sliding a blank by its center hole down the 0.5" threaded turning fixture rod onto the face of the jig and clamping it down using a nut and washer on the 0.5" rod, then from the reverse side of the jig, drilling a hole though the blank using one of the 60° spaced holes in the jig as a guide, (using the same bit the jig holes were drilled with, and drilling carefully to avoid enlarging the hole in the jig). With one hole drilled, a 6-32 threaded screw was inserted through the jig and blank both, and fastened in place using #6 fender washers and a 6-32 threaded nylon insert lock nut. With the blank firmly held in place by the center rod and the tightened screw, the remaining five holes could be drilled though the other jig holes, with registration guaranteed by the alignment of the jig. Placing screws through all six holes and fastening the blank firmly in place with fender washers and lock nuts allowed blanks to be machined as desired by turning the jig in a lathe via the turning fixture rod.

Anticipating later machining processes, the paint stirrer compass was used to scribe two turning limit circles on the blanks, one with the intended outer diameter of the stiffening rings, and one with the same diameter as the outside diameter of the volute ring.

[parts is parts] [parts is parts] [parts is parts] [parts is parts] [parts is parts]

Hold On:

Holes drilled in its stiffening rings and side plates could be used directly with screws and nuts for disassembling and reassembling the Mark-II turbine when changing test configurations. But, screws and nuts can be a pain in the butt. It also would be possible to thread the holes in the stiffening rings and turn screws directly into them to mount the side plates. At least for a while. Careful tightening would keep threads in the plastic intact, but, they would be very easy to strip. Nylon screws would help with the thread stripping issue, but, at the outset I wanted to give this turbine a sort of "nouveau old-world" look, with brass hardware and dark-finished wood construction, in combination with high-tech plastics. With that in mind, I decided to install 6-32 threaded brass inserts into the stiffening rings to allow easy and reliable installation and removal of the turbine side plates.

The brass inserts were the type normally used to provide standard machine screw threads in wooded projects. They have an interior threaded screw hole, and an exterior wood screw style thread, plus notches on one end that can be used to screw the insert into the appropriately sized pilot hole in a piece of wood. Screwing them into acrylic plastic really isn't feasible, but, gluing them with 5-minute epoxy is.


The six previously drilled 60° spaced 6-32 thread sized holes in the acrylic plastic ring blanks were drilled out to a diameter approximately 0.25" greater than the diameter of an insert. A small piece of waxed paper was pressed down over each of the six 60° spaced screws extending through the face of the alignment jig, and a brass insert run down each of the screws, slots up, to the point of clamping the waxed paper pieces to the face of the jig. Carefully, to avoid getting any on the inserts' outer threads, bee's wax was rubbed on the jig screws to prevent epoxy from sticking to their threads. Then a plastic blank was lowered onto the alignment jig center rod, passing its six enlarged holes over the jig screws and the brass inserts. After rotating the blank slightly, until its holes appeared centered around the brass inserts, the blank was clamped in place on the jig. The gaps between the inserts and their respective holes in the blank were filled with 5-minute epoxy to fix the inserts to the plastic. When the glue hardened, the tops of the inserts and the jig screws were buffed of with a small wire wheel, (to make sure the screws were free of glue), the screws removed by turning them out from the reverse side of the alignment jig, and the insert tops ground flush with the blank face using a small grinding stone; leaving six 6-32 threaded brass holes in the blank, aligned exactly with 60° spaced holes in the jig.

[inserts] [inserts] [inserts] [inserts] [inserts] [inserts] [inserts] [inserts]

Since the ring blanks needed to be stacked flat on the jig to allow turning them simultaneously to the same diameter on a lathe, the inserts in the second blank had to be installed such that their threads were aligned with the threads of the inserts in the blank with inserts already glued in place as though pairs of inserts formed one continuous threaded hole from one ring blank through the next blank when the blanks were stacked. This was accomplished by reinserting the jig screws in the alignment jig, screwing them through the inserts in the first ring blank in the process, then repeating the insert installation process with second blank clamped to the first blank, rather than to the face of the alignment jig.

[2nd inserts] [2nd inserts] [2nd inserts] [2nd inserts]

The treaded inserts were installed in the stiffening ring blanks before machining the blanks to their final form because it would have been extremely difficult to properly align the inserts once the center portions of the blanks were cut out to form the actual rings.

Line Up:

With 6-32 threaded brass inserts properly aligned and epoxied into the acrylic plastic stiffening ring blanks as described in the "Hold on" subsection above, and close fit 6-32 thread sized holes drilled in an acrylic plastic blank intended for one of the Mark-II turbine side plates, all three blanks were mounted on the combination alignment jig and turning fixture, with the two ring blanks underneath the side plate blank.

The previously scribed turning limit circles on the ring blanks were set facing outwards from the face of the turning jig. With the jig screws turned out until their ends were flush with the face of the side plate blank, the paint stirrer compass was used to scribe a turning limit circle of the intended outer diameter of the stiffening rings on the face of the side plate blank.

[side pieces] [side pieces] [side pieces] [side pieces] [side pieces]

With the blanks aligned and scribed, one by one, the jig screws were removed from the back of the turning fixture and reinserted through the face of the side plate blank and screwed through the brass inserts in the underlying ring blanks until a washer on each screw was firmly clamped to the side plate blank face. This process not only firmly clamped all three blanks together, but, also pointed the sharp ends of the screws away from the lathe work area. (Safety first!) With all six screws reversed, washers and nylon insert nuts were used to fix the blank stack to the turning jig via the screws extending through the alignment holes.

[side pieces] [side pieces] [side pieces]

With everything aligned and firmly fixed in place, as a unit the blanks and turning fixture were trimmed down to just outside the turning limit scribe line on the side plate blank using a jigsaw. This minimized the amount of material that would need to be removed by the lathe in machining the blanks to their final outer diameter.

[side pieces]

After the rough trimming, the turning fixture was mounted in a lathe, and all three blanks were simultaneously machined down to their final outer diameter, referenced by the earlier applied turning limit scribe line.

[side pieces] [side pieces] [side pieces]

The final step before moving on to cutting out the central portion of the stiffening ring blanks was to use an electric hand drill to bore a 0.0625" registration hole through all three blanks near and just inside one of the 60° spaced holes in the side plate blank while the blanks were all still mounted on the turning fixture.

[registration] [registration]

Although everything was very well aligned in the construction process, if one of the rings was turned upside down relative to its initial alignment position at a later time, this could result in hole misalignments. (Nothing is perfect!). Always making sure the registration holes are aligned when later assembling and disassembling the Mark-II turbine will eliminate this potential problem.


With the two stiffening ring blanks and the side plate blank turned to their mutual final outside diameter, the side plate blank was removed from the stack on the turning fixture, to allow machining of the stiffening ring blank centers. To maintain alignment of the ring blanks while the side plate blank was detached, first just one of the turning fixture screws was removed, then reinserted through the back of the turning fixture and screwed through the threaded inserts of both ring blanks. Then, the remaining screws were removed and the side plate blank set aside. All screws were then reinstalled through the front side of the turning jig, with washers and nylon-insert lock nuts, once again fixing the still aligned ring blanks to the jig.

[side pieces] [ring pieces] [ring pieces]

The two stiffening ring blank centers were first cut out, and the ring centers trimmed outward to close to the previously scribed turning circle on the face of the outermost ring blank using a standard cutter in the lathe tool mount. With the centers cut close to their final inside diameter, the standard cutter was switched to a boring cutter, and machining of the rings was completed. To be certain the outer diameter of the volute ring was a close fit in the stiffening ring inner diameter, the lathe was occasionally stopped and the center cut compared to the outer diameter of the volute ring. With their centers cut to size, the completed stiffening rings were removed from the turning jig, ready for later final assembly.

[ring pieces] [ring pieces] [ring pieces] [ring pieces] [ring pieces]

Slip 'n:

To make the Mark-II turbine design as flexible as possible for testing different runner configurations, an adjustable side plate was included in its construction. With a side plate who's distance from the opposite side plate can be adjusted by slipping it inside the volute ring, tests can be made with runners having different numbers of discs, and hence different widths.

A second ring of 60° spaced holes was drilled in the alignment jig inside of the first set of holes, on a radius that placed them about 1" within the inside diameter of the turbine volute ring. A piece of 0.236" thick acrylic plastic sheet was cut into a octagon to use as a blank for the adjustable side plate. The new set of holes in the alignment jig was then used to aid installing 6-32 threaded brass inserts in the blank by the same method employed to install inserts in the volute stiffening rings and full-sized side plate.

[slide side] [slide side] [slide side] [slide side] [slide side] [slide side] [slide side] [slide side] [slide side] [slide side]

The turning fixture mounting disc was flat, but, in cutting out the centers of the turbine volute stiffening rings, the face of the disc was grooved at the same place the second ring of 60° space holes needed to be drilled. To avoid flexing the outer edge of the adjustable side plate blank when attaching it to the fixture, the disc face was first smoothed off in a lathe before mounting the blank for turning.

[o-ring] [o-ring]

A significant amount of the material to be removed from the adjustable side plate blank was ground off using a sanding drum in a drill press. The blank was then mounted on the turning fixture, and machined to its final outside diameter. After the final diameter was achieved, a triangular cutter was used to cut a groove in the outside edge of the adjustable side plate to retain an o-ring intended to seal the adjustable side plate to the inner diameter of the turbine volute ring.

[o-ring] [o-ring] [o-ring] [o-ring]

A length of 0.0938" inside diameter automotive vacuum hose was used to create an o-ring. The hose was cut so that when wrapped loosely around the groove in the adjustable side plate edge, a gap of about 1" remained between the cut ends. A piece of 0.0938" polystyrene hobby tubing approximately 0.75" long was coated with cyanoacrylate glue and both ends of the vacuum hose were pushed to the same depth over the polystyrene tube, completing the o-ring.

[o-ring] [o-ring] [o-ring]

Stick Up:

(c.a., June 2007)

The volute stiffening rings were attached to the volute ring using high-strength "plastic weld" quick-hardening epoxy glue. A length of cardboard was trimmed to have parallel edges at a width that held the stiffening rings apart at a distance so that their outward facing edges were about 0.0625" past the edges of the volute ring. The strip was cut into four pieces, the four pieces accordion folded for strength, and then taped in place using 2" wide packing tape to support and locate the stiffening rings in their final position on the volute ring. With the stiffening rings in place, the gap formed below the outer edges of the stiffening rings and the edges of the volute ring were filled with mixed epoxy.

[attach rings] [attach rings] [attach rings] [attach rings]

When the epoxy hardened, the cardboard strips between the rings were removed, a filleting tool was cut from a plastic putty knife, and more mixed epoxy was applied to the inner edges of the stiffening rings seated against the outer face of the volute ring using the filleting tool. Dipping the tool in water helps keep the epoxy from clinging to the tool and "globbing" underneath it when forming the glue fillet in the corner between the rings.

[attach rings] [attach rings]

Once all the epoxy hardened, the epoxy in the outer edge gaps was ground down with a fine sanding drum mounted in a Dremel™ tool, until the glue filling the gaps was flush and square with the face of the stiffening rings.

Slide 'n:

(c.a., July 2007)

With the adjustable side plate and o-ring complete and the volute stiffening rings cemented in place, six 0.236" thick strips of acrylic plastic 1" wide were cut and drilled with two holes each to align with a pair of the 60° spaced threaded inserts, one in a volute stiffening ring, and one in the adjustable side plate. The lengthwise placement of holes in the strips was determined by setting the adjustable side plate with o-ring in place into the volute ring, and threading a long 6-32 thread screw into one of the brass inserts in the adjustable plate. Marking the position of the long screw's contact with a long plastic strip laid across the volute stiffening ring and also marking the position of the brass insert in the volute stiffening ring paired with the insert holding the long screw gave the separation for holes to drill along the center line of the plastic strip.

[standoffs] [standoffs]

Inserting 6-32 thread flat head screws backed up with decorative brass fender washers through the holes in the plastic strips and tightening the screws into the paired brass inserts firmly attaches the adjustable side plate just inside the outer edge of the turbine volute ring.

[standoffs] [standoffs]

To simplify assembly when the plastic strips are used with longer screws and brass tube stand-offs to set the adjustable plate inside the turbine volute ring, a nonpermanent ink line was drawn around one of the decorative brass washers on each plastic strip, the strips removed, and the hole within the drawn circle was elongated to fit just inside the circle. The ends of the plastic strips were then rounded against a drum sander mounted in a drill press.

[standoffs] [standoffs] [standoffs] [standoffs] [standoffs]

I couldn't find my tubing cutter when it came time to make the brass tubing standoffs. Double nutting on a 6-32 thread screw, with the nut closest to the threaded end of the screw set so its face was the distance from the end of the screw desired for the standoff length provided a fixture for precisely grinding thin wall brass tubing roughly cut with a hacksaw to the proper length against an electric grinder stone.

[standoffs] [standoffs] [standoffs] [standoffs] [standoffs]

The standoff assembly is, in order, on a long 6-32 thread flat head brass screw, a decorative brass fender washer, the elongated hole end of a 1" plastic strip, a 6-32 brass washer, a brass tube standoff, and a second 6-32 brass washer. The screw in the middle of the standoff assembly is threaded into one of the brass inserts in the adjustable side plate, and a short 6-32 thread flat head screw, backed up with a decorative brass fender washer, is threaded into one of the brass inserts in one of the stiffening rings. Doing this for all six pairs of brass inserts aligned between the stiffening ring and the adjustable side plate, then tightening the screws, fixes the adjustable side plate at a distance equal to the length of the brass tubing standoffs and two brass washers inside the volute ring. The long brass screws threaded into the adjustable side plate are cut so they end flush with the inner face of the side plate.

[standoffs] [standoffs] [standoffs]

Broad Side:

The full size side plate is attached to the turbine volute using 6-32 thread screws backed up by decorative brass fender washer inserted into the brass inserts embedded in the volute stiffening ring opposite the stiffening ring used to mount the adjustable side plate.

[full side] [full side]


Make A Stand:

Building the Mark-II turbine stand from wood, so that the volute ring sits centered on, parallel to the edges of, as well as perpendicular to the surface of the turbine base, while providing support for turbine runner axle uprights that allow precise alignment so the axle passes through the volute ring both centered and parallel, with a durable construction that allows easy and repeated disassembly of the turbine while testing different configurations, and, in the end, looks pretty, took a fair amount of attention to details during the construction process. The steps that were required to accomplish this task are outlined in the subsections below.

Set Up:

(c.a., May 2007)

The Mark-II turbine volute ring is mounted on two 8" tall commercially produced pinewood shelf brackets. The corners of the shelf mounting arms of the brackets were marked to cut for volute ring supporting surfaces using the ring as a guide, and roughly rounded off with a jigsaw so that at its lowest point the upright volute ring sat approximately 2.5" above the bracket wall mount surfaces. The volute ring mounting brackets are attached to a commercially laminated 0.5" thick pinewood base, 24" long by 18" wide.

[ring mounts] [ring mounts] [ring mounts]

(c.a., June 2007)

To make a close fit of the volute ring to the shelf bracket rounded cutout areas, those areas were sanded smooth and square using a drum sander mounted in a drill press. The squareness of the shelf supports to the sanding drum was established by resting the bracket shelf support pieces on a small stack of 0.5" thick wooden blocks on the drill press table. The cutout areas were sanded smooth to the same radius, making the final distance the volute ring would sit off the turbine base plate approximately 2". The brackets were set upright on their wall mount surfaces on the turbine base board, and a thin layer of sawdust-and-glue mix type wood filler applied to the upward facing curved cutout areas. After laying strips of waxed paper over the wood filler to prevent sticking, the volute ring was sat on the waxed paper and pressed down into the filler to form exact fit surfaces for the volute ring on the modified shelf brackets. The sealed split in the volute ring was used for alignment by centering it in the rounded cutout region on one of the shelf brackets, (both now formally modified into volute ring mounting brackets), and marking its position on the mounting bracket.

Forming the wood filler surfaces was done before the volute stiffening rings were glued to the volute, and one of the rings was slid on to the volute so that with the volute ring sitting centered on the mounting brackets, the stiffening ring contacted both brackets squarely to keep the volute aligned with the brackets while the wood filler hardened, (and to keep the volute ring from falling over). Even after the stiffening rings were attached to the volute, always assembling the turbine with the volute ring split aligned on the mounting bracket with the mark draw during the wood filler surface forming process guaranteed the volute ring sat properly on the filler surfaces during turbine construction.

[ring mounts] [ring mounts]

Straighten Up:

(c.a., July 2007)

Aligning the Mark-II turbine volute ring and runner axle so that the axle passed through the volute ring on center and perpendicular was accomplished in several stages. First the mounting brackets were placed on the turbine base plate and the volute ring set on the mounting brackets to establish their proper spacing. The entire volute ring and mounting block combination was then centered on the turbine base plate. The volute ring was lifted from the mounting brackets, and the mounting brackets tapped gently, side-to-side only, to move the mounting surface edges in line relative to a steel ruler. Predrilled mounting holes in the mounting brackets had a close fit for #8 wood screw threads. Marks were made with a transfer punch through the predrilled mounting holes. The brackets were moved out of the way so the transfer punch marks could be center punched and pilot holes drilled for #8 flat head wood screws. A mark was made on the turbine base plate under the area covered to by the bracket that previously was marked to show where to align the split in the volute ring to indicate the proper set of mounting holes for that bracket after later removal and remounting of the brackets during the turbine construction process. Flat head #8 wood screws were pressed through the bracket mounting holes, the screw ends used to align the brackets with their proper set of pilot holes, and the screws tightened down, using bee's wax on the threads to ease insertion and removal.

[ring mounts] [ring alignment]

Precise cut oak strips 2" wide and 0.5" thick were purchased at a hardware store to use aligning the volute ring parallel to the turbine base plate edge. A notch was cut in one end of two strips so that square ends could be set to touch the edge of one of the volute stiffening rings without being interferred with by the volute ring mounting blocks. The horizontal distance from the edge of the turbine base plate to the center of the volute ring when the volute ring sits upright centered on the base plate and parallel to the edge of the base plate was determined, and that distance marked on both of the notched oak strips, measuring from the square ends extending over the notch. These marks were aligned exactly on one edge of the turbine base plate and the strips set perpendicular to the base edge with a small square so that one strip's notched end was close to the inside edge of each of the volute mounting blocks, then the strips were fixed in place with a c-clamp. Setting the volute ring on its mounting blocks, with the sealed split aligned on the correct mount, then moving the volute over until the closest stiffening ring contacted both the strips centered the volute and also aligned it parallel with the edge of the turbine based plate.

[ring alignment]

On the opposite side of the turbine base plate from the clamped down 2" wide alignment strips, a carpenter's square c-clamped to a 0.5" square steel bar was set against the base plate and volute ring to hold the volute ring perpendicular to the base plate.

[ring alignment]

With the volute ring perpendicular and parallel alignment fixtures in place, the volute ring was lifted off its mounting blocks, and a final thin coat of sawdust-and-glue mix wood filler smeared over the volute mounting surfaces. Again using waxed paper to prevent sticking, the volute ring was set back down on its mounting blocks, (making sure the ring split was aligned on the proper mounting block), pressed into the wood filler, and set back against the alignment fixtures. The last coat of wood filler insured the volute ring would be fully supported in its final perpendicular and parallel placement on the mounting blocks. It is important the volute ring is fully supported in the mounting blocks, or when the ring is fixed in place using screws there is a high risk of cracking the acrylic plastic.

[ring alignment] [ring alignment] [ring alignment]

Stick Down:

With the final coat of wood filler support material hardened, eight marks were made inside the Mark-II turbine volute ring for drilling screw holes, four over each mounting block support surface, in an offset pattern to make it impossible to install the volute ring with the ring split over the wrong mounting block. The volute ring was then lifted from its mounting blocks, and three strips of wood used for gentle but secure clamping of the volute ring into a large mechanic's vice. With the ring in clamped in the vice, the eight marks were drilled to give a loose fit for #6 wood screw threads, stepping up from a 0.0625" drill through several sizes to avoid cracking the plastic. The holes were then counter sunk so the heads of the flat head brass screws used to attach the volute ring to its brackets are flush with the inside surface of the ring.

[ring attachment] [ring attachment] [ring attachment] [ring attachment] [ring attachment] [ring attachment]

The final wood filler layer on the volute ring mounting blocks was lightly sanded, the volute ring set back in place its with split aligned on the proper mounting block and set square in the parallel and perpendicular placement setup fixtures, then marks drawn on the block mounting surfaces through the screw holes.

[ring attachment] [ring attachment]

It is exceptionally important when installing screws close to the edge a piece of wood, particularly when it is not particularly hard wood, to drill deep pilot holes for the screw threads, and, in the case of screws with an unthreaded shank section, drill out the upper part of the pilot hole to relieve the stress that would otherwise be exerted on the wood by pulling the unthreaded section into the pilot hole. Without taking these precautions, it is almost guaranteed the wood will split out, and possibly ruin the work piece. To avoid this happening to the volute ring mounting brackets, 0.0625" pilot holes were drilled deeper than the length of the #6 flat head brass screws used to attach the volute ring to the mounts in the center of the screw hole marks, and a drill bit slightly larger than the unthreaded shank section of the screws was marked with tape to indicate the depth to drill to relieve the pilot holes for the unthreaded part of the screw. With the holes all drilled and relieved, the parallel and perpendicular alignment fixtures were removed, and the volute ring attached to its mounting brackets using #6 brass screws, with, as always, bee's wax applied to their threads to ease insertion and later removal.

[ring attachment] [ring attachment] [ring attachment] [ring attachment] [ring attachment]

Second Base:

(c.a., September 2007)

The main base of the Mark-II turbine consists of a 24"x18" piece of commercially prelaminated pine board 0.5" thick. To add rigidity to the base, and provide support for the turbine runner axle uprights, the base board was ringed around its bottom side with 4" wide pine board 0.5" thick. After the under edge pieces were installed using white woodworking glue and #8 flat head wood screws, the basic base form was completed by marking then rounding all four corners to a 3" radius using a jigsaw followed up by a drum sander mounted in a drill press, and shaping the top edges using a 0.25"x0.625" bearing-aligned Roman Ogee bit mounted in a woodworking router.

[base edge] [base edge] [base edge] [base edge] [base edge] [base edge]

Run Around:

Although the volute ring is attached squarely on the Mark-II turbine base, square is not a term that can be applied to the shop floors, or to any of the benches in the assorted places I do my turbine construction work. That means levels, lasers, and the like are not going to be too helpful in finding the center of the volute ring, nor in setting an axle through the center of, and square to, the volute ring, so the runner discs spin true. But, getting discs to run true in the volute ring is the primary task for this section.

That I don't have a genuinely level surface to work on isn't a big problem. I've always been a bigger fan of geometry than measuring. I rarely actually measure things other than to set a gross overall size in building something like the Mark-II turbine stand. (Most of the time I only can report exact size of a specific component because someone has asked me about it, and I go and measure it after the fact.) Geometrically finding the center of the volute ring, setting the axle support uprights, and finally aligning the runner axle and discs is a pretty straight forward task, though it does involve a number of steps. Those steps are outlined in the subsections that follow.

Squaring a circle:

To find the center of the turbine volute, thin cardboard pieces were taped together to form a single sheet larger than the outside diameter of the volute stiffening rings. The taped together sheet was pressed against one of the volute stiffening rings, and reaching through the other volute stiffening ring, an ultra-fine line permanent marker was used to mark the inside diameter of the volute ring on the cardboard. The cardboard was then trimmed to about the outer diameter of a volute stiffening ring, and four squares of the same cardboard material were taped around the diameter of the trimmed disc to provide a drawing surface on which to enscribe a box around the circle. (Yes, those paying attention have already recognized the initial trim and tape operation as an unnecessary step. (I was thinking of doing something else first, changed my mind, and didn't want to waste the material.)) A carpenter's square with arm lengths greater than the diameter of the drawn circle drawn was set so both arms of the square touched the circle tangentially, and a line was drawn down the arms to form two lines tangent to the circle intersecting at a 90° angle. Two more tangent lines, one parallel to each of the first pair, define a square box that can be used to mark the geometric center of the circle.

[center template] [center template] [center template]

Don't, as the first photo in the set below this paragraph implies, just flop the carpenter's square over 180° to draw the second set of tangent lines. Doing this will most likely result in a rhombus that is not square and won't be useful for accurately marking the center of the circle. Work the square around the circle, using one of the first tangent lines for aligning the square to draw another tangent that intersects the tangent used for alignment at 90° and is parallel to the other tangent of the first drawn pair. Then use the just drawn tangent to align the square to in order to draw the last tangent line, parallel to the first line used for alignment, and intersecting the current alignment line at 90°. This two step process leaves the square rotated 180° around the circle. The intersection of the diagonal lines drawn from corner-to-corner of the square enscribed around the circle marks exactly the geometric center of the circle. With the center of the circle marked, the carpenter's square was used to draw perpendiculars relative to the enscribed square that pass through the center of the circle.

[center template] [center template]

Trimming out the drawn circle into a disc with close fit in the volute ring, and taping the disc's unmarked side to a block of wood resting in the volute ring allowed the angle of the lines on the face of the disc to be adjusted relative to the center of the volute ring by adjusting the angle at which the wood block was sitting in the ring.

[center template] [center template]

Aligning one of the lines that pass though the center of the cardboard disc with a carpenter's square resting on the turbine base allowed vertical registration marks to be drawn on the volute stiffening ring that define a line perpendicular to the turbine base passing through the turbine volute ring center. The line marked on the cardboard disc perpendicular to the line used to align the carpenter's square allowed horizontal registration marks to be drawn on the volute stiffening ring that define a line parallel to the turbine base passing through the turbine volute ring center.

Making a mark on the turbine base plate at the corner of the carpenter's square when the square was aligned with the vertical line on the cardboard disc allowed a line to be drawn perpendicular to the volute ring inner surface and directly below the geometric center of the volute ring. Since the volute ring surface was set perpendicular to the edges of the turbine base plate in its mounting process, a carpenter's square could be used to draw the line on the base plate by aligning one arm of the square with the edge of the base plate and aligning the other arm with the mark on the base plate. This line was later used as an aid in setting the runner axle support uprights in their proper positions.

[center template] [quad marks] [quad marks] [quad marks] [quad marks]

Picking a pocket:

The line previously marked on the Mark-II turbine base plate directly below the geometric center of the volute ring and parallel to the volute ring face defined the proper "fore-and-aft" position for the center of the runner axle support uprights. The "port-and-starboard" positions of the uprights were selected so that the inner edge of an upright falls exactly on the inner edge of its respective 4" wide support board previously glued and screwed to the underside of the turbine base.

The volute ring and volute support brackets were removed from the turbine base, and the position of the inner edge of the uprights was marked on top of the turbine base by laying a 4" board along each edge of the base, aliging the outer edge of the board exactly with the edge of the base using a small square, then marking the spot where the inner edge of the board crossed the previously drawn line. A carpenter's square was then used to draw a perpendicular through both intersection points. The outer edge of the uprights was marked by laying on edge a piece of the 0.75" thick oak board to be used for the uprights along the perpendicular lines, and marking new perpendiculars along the oak board edge closest to the turbine base edge. To avoid confusion over which line is which when later using a router jig to cut a pocket, (more correctly, tenon, in woodworking parlance), in the base for each upright, the perpendicular lines defining the upright pocket inner edges were scribbled over.

[axle uprights] [axle uprights] [axle uprights] [axle uprights] [axle uprights]

The upright pockets were cut using a 0.375" straight cutter chucked into a plunge router, with the router retained by a jig that precisely constrained the cut limits to the size of a pocket. The jig was constructed by squarely attaching 1" wide by 0.75" thick square edged strips of wood onto a 0.5" thick piece of plywood. The plywood was cut to be longer than the width of the router base, (6"), plus the width of an axle upright, (4"), plus two more inches for wood strips, and, cut wider than the width of the router base, plus the thickness of an axle upright, (0.75"), plus two more inches for wood strips. To avoid problems with the strips moving when they were attached to the plywood with #6 flat head wood screws, holes were predrilled and counter sunk in the strips so that the only screw threading happened in the plywood.

After the first corner pair of 1" wood strips were attached squarely to the plywood, and the plywood oriented so the corner formed by the 1" strips was to the lower left of the rectangle being formed for the jig, the position for the next 1" strip was determined by setting the router body (with cutter retracted) in the corner, contacting both 1" strips, and laying a piece of the 4" wide oak board to be used for the axle support uprights on its wide side in contact with the right edge of the router base. Using a carpenter's square to align the edge of the 4" board away from the right side of the route base perpendicular to the bottom edge 1" strip while maintaining contact between the 4" board and the router base placed the 4" board so that its right edge was at the proper position for aligning the left edge of the right side 1" strip, and a pencil mark was drawn down the right edge of the 4" board. (Don't worry! We'll deal with the issue of the half-width of the cutter shortly.) Clamping the predrilled 1" strip so its left edge aligned with the pencil mark, (some light tapping with a hammer ensued), the strip was screwed to form the right edge of the jig rectangle. Cutting the last 1" strip to fit between the left and right side 1" strips, the same process employed to set the right side strip was used to position the top side strip, only the 0.75" wide end of the 4" wide oak board was used to space the 1" strip from the upper edge of the router body.

The jig's 1" wide strip limit the motion of the router so that its cutter can move only within a 4" by 0.75" rectangle, as defined by the widths of the board use to set the strips away from the router base. Well...almost. Actually, as placed, the strips restrain the center line of the router cutter to a rectangle defined by the widths of the board used to set the strips in place. Since the router cutter has diameter greater than zero, the cut using the jig with the 1" strips alone would be one-half the width of the cutter too wide in all directions. None-the-less, the first router cut on the jig was to open up a hole in the plywood piece using the 1" edge strips as they were initially placed. This was mainly to avoid having to cut through the plywood piece when making the first cut of a pocket in the turbine base.

Two halves make a whole, and the whole cutter was 0.375" wide, so two 0.375" wide wooden strips were cut, one screwed to the inside of the jig's right edge strip, and one screwed to the inside of the jigs top side edge strip. That compensated for the double half-width oversize cuts as defined by the 1" strips alone.

Two full-width compensating strips were use for two reasons: (1) because it was easier than making and installing 4 half-width strips, one on each inside edge of the 1" strip rectangle, and, (2) because the full compensation is to one side only, the edges of the initial cut hole in the plywood opposite to the compensation strips align exactly with the edge of the cutter when using the jig, and, hence, those initial cut hole edges can be used to align to marks defining the position of any pocket the jig is to cut.

Note that while not all routers do, the router used in aliging the pocket cutting jig has a flat side on its otherwise round base. That edge must always be against the side it was against when constructing the jig, or pockets will not be cut in the correct location. That side was clearly marked on the jig. When using a fully-round base router, this is not an issue.

[tenon jig] [tenon jig] [tenon jig] [tenon jig] [tenon jig] [tenon jig] [tenon jig] [tenon jig] [tenon jig] [tenon jig] [tenon jig] [tenon jig]

The router jig was then aligned to the edge and center lines previously drawn on the base, then used to cut the first pocket. Note in the close-up image of the jig cutout in the photo sequence below how the edge opposite of the top edge width-compensating strip was aligned with the outer edge pocket line on the turbine base, and also how the axle center line was aligned to a mark one-half the cutter width towards the right edge width-compensating strip away from the actual center of the 1" strip rectangle. These alignments put the outer edge of the final router cut on the outer edge pocket line and centered on the axle center line. With the jig aligned, the router was plunged though the router base to a depth of about 0.25" into the under base edge stiffening board, and the entire area of the pocket cutout removed my sliding the router around the inside limits of the jig. The rounded corners of the cutout (due to the cutter being round) were removed with a narrow, sharp chisel, completing the axle support upright pocket.

[axle uprights] [axle uprights] [axle uprights] [axle uprights]

Before the volute ring and mounts were removed from the turbine base, a square cut piece of cardboard was marked to indicate the height of the geometric center of the volute ring, using one of the marks previously drawn at that height on the volute stiffening rings as a guide. Using the premarked cardboard piece, the height of the center line was marked on a 4" wide board set in the pocket cut in the turbine base. That board was cut 3" longer than the center line mark, and the remainder of the board cut to the same length as the end inserted in the pocket. With two suitably long axle support uprights, the router jig was moved to the other side of the turbine base and the second pocket cut.

[align axle] [align axle] [align axle] [axle uprights]

With both pockets cut and both axle support uprights cut to length, the uprights were prettied up a bit by rounding their upper corners and shaping their edges with a 0.25" bearing backed coving cutter chucked into the router. After shaping the uprights, the volute mounting brackets and volute ring were reinstalled on the turbine base, and the axle support uprights set in place.

[axle uprights] [axle uprights] [axle uprights] [axle uprights] [axle uprights] [axle uprights] [axle uprights] [axle uprights]

Coming around:

For simple axle alignment purposes, there is no need for a full runner assembly in the turbine volute. Two runner discs set on an axle, one close to, but inside, either edge of the volute ring will suffice. Two 11.625" diameter discs with 0.5" diameter center holes were cut from 0.091" thick acrylic plastic sheet; mounting them in a lathe employing the same jig used to turn the volute stiffening rings and end plates. Due to the thinness of the material, the 0.5" diameter center holes were drilled carefully, backing up the blanks with wood, clamping them to the drill press table, and stepping up through several drill sizes to reach the final 0.5" size drill. With the blanks turned round with center holes, they were mounted between washers and nuts on a piece of US standard thread 0.5" diameter rod separated by a distance about 0.5" less than the width of the volute.

[runner discs] [runner discs] [runner discs]

With the alignment runner axle assembled, one of the axle support uprights was removed and the other left in place in its pocket on the turbine base. The position of the two runner discs on the 0.5" was adjusted so one end of the rod touched the face of the in-place axle support upright with the discs inside the volute ring. The discs were then supported at three places by thin cardboard strips so that the discs sat centered in the volute ring. With the discs centered, the position of the end of the 0.5" rod against the axle support was marked, and that position drilled to 0.5" diameter. The process was then repeated to mark and drill the second upright. With both uprights drilled, the axle was set centered through both holes and the position of the discs reset to place one near but inside each edge of the volute ring.

[align runner] [align runner] [align runner]

Run free:

For final alignment, the axle needed to spin freely so that binding and rubbing of the runner discs in the volute could be easily detected. Two bushing were made by drilling out a piece of 0.5" outside diameter brass tubing found in one of my many junk boxes, (I believe it started life as some kind of blow-torch nozzle), to a 0.3125" inside diameter, then turning both ends of the 0.5" diameter threaded rod runner axle down to 0.3125" and buffing them off with medium grit emery paper and crocus cloth until the drilled-out brass tubing turned smoothly on machined ends of the axle rod. The tubing was then cut in half and one piece inserted into the 0.5" holes in the axle uprights to act as axle bushings.

[axle bushings] [axle bushings] [axle bushings] [axle bushings] [axle bushings] [axle bushings] [axle bushings]

Stand tall:

The final axle alignment was made using thin brass shim material underneath the ends of the axle support uprights in the pockets cut in the turbine base. Since the pockets were cut down into the under-edge stiffening boards so that their inside edges aligned with the inside edges of the stiffening boards, the inner edge of the lower part of the pockets was open to the inside of the underside of the turbine base. Thus the axle support uprights could be set in place and clamped firmly to the base against square blocks, then tapped with a rubber hammer to adjust the position of the runner discs so that they spun freely within the volute ring. With the discs aligned and the uprights firmly clamped in place, the brass shim material could be placed under the supports via the open side of the pockets in the inner edge of the base stiffening boards. Counter-sunk pilot holes were drilled through the base edge stiffening board, through the shim material, and into the ends of the turbine support rights to accept #6 flat head wood screws. The screws were coated with bee's wax, then threaded through the edge stiffening boards and into the ends of the axle supports to mount them firmly in place at the proper height for the runner to spin freely in the volute ring.

[upright shims] [upright shims] [upright shims] [upright shims] [upright shims] [upright shims] [upright shims] [upright shims] [upright shims]

Last Call:

After the Mark-II turbine had its volute ring and axle support uprights aligned and mounted, the volute and its mounts were removed from the turbine base. The volute mounts were reinstalled using white wood working glue as well as screws, and wooden dome plugs glued into the volute mount screw holes. The volute ring was left off and the base assembly was sanded smooth, then finished with dark mahogony stain and coated with polyureathane spray varnish. After the varnish dried, eight rubber furniture-leg coasters were installed with wood screw through holes drilled in their centers as feet around the under base edge stiffening boards, the volute ring reinstalled in its mounts, and the runner axle assembly and turbine end plates installed. Brass flat head screws and decorative brass fender washers were used in mount the end plates to the threaded brass inserts embedded in the volute stiffening rings.

[finishing] [finishing] [finishing] [finishing] [finishing] [final assembly] [finishing]

In no small part because the final unit seemed a little too spartan for the look I was trying to achieve for the Mark-II turbine, I added decorative black-iron shelf mounts as gussets to the inside of the axle support uprights, using #8 pan head brass screws. In fact, the brackets don't just enhance the look of the Mark-II turbine, but also add some side support to the axle uprights that should help the unit's alignments survive for many reassembly cycles to come.

[finishing] [finishing] [finishing] [finishing]

The final step in finishing the Mark-II turbine basic assembly was to fix the position of the temporary alignment axle between the axle support uprights. Two 0.3125" thread nuts were drilled out to give them clear 0.3125" holes, and 0.125" set screws added through one face of each nut, creating two locking collars. With the runner assembly properly centered in the volute ring, these collars were placed lightly against washers slipped over the ends of the alignment axle on the outside of the axle support uprights, and the set screws tightened to retain the axle between the uprights, while allowing the axle to spin freely in its brass bushings.

[final assembly] [final assembly] [final assembly] [final assembly] [final assembly]


Shine On:

(c.a., June 2007)

It's hard to miss in a good percentage of the photos presented in the Mark-II turbine basic assembly sections above, that the volute ring is scratched and scuffed and globbed with glue, while in other images it isn't. Some of the unscuffed images are just that, photos taken before the acrylic plastic surfaces were abused, but, others are from after those same abused surfaces were ground, sanded, buffed, and shined back into a more presentable state.

Initially some effort was put into protecting the volute and volute stiffening ring surfaces during the construction process. But, schedules are very tight, (doing the bulk of this work in three different places, separated by about 350 miles, mainly only with the time available on the odd holiday break or day off), and, sometimes you simply run out of masking tape 5 miles from the nearest store, and don't have the time to run and get some more, even if you could justify a trip to town for just one roll of tape. Eventually, expediency gave way to neatness, and what need to be done just got done; all the while knowing it is possible to refinish damaged acrylic surfaces, and, never having tried, also a bit curious about how difficult it was to do. Turns out that, albeit a little time consuming, even for somewhat severely damaged acrylic plastic it isn't that difficult to restore the surfaces to a reasonable finish.

Taking a educated guess at the necessary materials I picked up a few grades of standard sand paper, (80, 120, 180, and 340 grit), along with several grades of automotive wet-dry sanding paper, (600, 800, 1200, and 1600 grit), two grades of stick form rub on polish, (#3, and #6), and a can of aerosol acrylic polish. For use with the stick polish I also picked up a drill mandrel and two muslin buffing wheels. To keep from cross contaminating the buffing wheels, they were label for use with only one of the grades of stick polish, and, to keep them clean, sealed in a labeled plastic sandwich bag when not in use. An electric orbital sander, a Dremel™ tool with a sanding drum and supply of 80 grit sanding cylinders, a container for water, and big pile of newspapers rounded out the selection of polishing materials.

[implements] [implements] [implements]

The first step in refinishing the volute was to use the Dremel™ tool with sanding drum to smooth and square rough epoxy glue edges, and feather out areas with deep gouges. When the grinding was completed, standard dry sanding paper, stepping from 80 grit to 180 grit to 340 grit, was used to hand sand surfaces to a smooth to the touch, but milky appearing finish. (Using an electric orbital sander is allowed, of course.)

[rough start] [rough start]

With the dry sanding completed, the process was switched to wet sanding. A stack of newspaper was used as a nonabrasive, water absorbing support surface for the wet sanding operation. The basic wet sanding process is pretty straight forward. Keep things wet and starting with the most coarse grade of paper, sand the surfaces in a random rubbing pattern until it seems that the surface will get no smoother with the current grade of paper, then switch to the next less coarse grade of paper. Working through the wet sanding grades by hand is certainly doable. But, using an orbital sander has three advantages, (1) your hands aren't constantly wet and skin pruned, (2) it takes much less time than hand sanding, and, (3) it provides a much more random sanding pattern than hand sanding which leads to a better finish.

[wet sand] [wet sand]

Sanding flat surfaces is easy. Sanding circular items with narrow perpendicular edge surfaces, like the volute ring, is a bit more difficult. And, using an electric sander can increase the difficulty because of issues with properly orienting the sanding pad. Though, usually where there's a will there's a way. For example, setting the orbital sander's pad crosswise in the ring allows the edges of the pad to work in the ring. Using this technique its a good idea to fold the edges of the sand paper that aligns with the working edges of the sanding pad so that they extend just slightly out from the edges of the pad to insure good contact with the surface being sanded. Working the inside edges of the stiffening ring can be done in similar fashion, using just one corner of the sanding pad. Of course, some hand sanding is unavoidable.

[wet sand] [wet sand] [wet sand]

The most difficult area to sand on the volute was the outside surface between the stiffening rings. Being less than 2.5" wide, working that space by hand, at least if your hands are a big as mine, would not be easy to do. And, since that area on this project was the one with the most "mess" left after construction, hand sanding would have been a lot of work, even if the space was more easily accessible. That problem was solved by mounting half of a rubber hand-sanding block to the orbital sander so that it extend down from the sanding pad with a width less than the space between the stiffening rings.

To mount the block to the sander, a sheet of thin aluminum was cut to standard size for sand paper intended for use with the sander and the ends of the cut sheet bent to fit in the normal sand paper holding clamps. A curved-face rubber hand-sanding block was cut to width to fit lengthwise between the volute stiffening rings, making sure at least one of the sand paper retaining pins was left on each end of portion of the sanding block to be mounted on the electric sander. A 0.75" thick block of wood was cut to the same perimeter size as the back of the cut rubber sanding block for use as a spacer between the sanding block and the aluminum sheet clamped to the electric sander's pad. Three counter sunk holes were drilled through the rubber sanding block for #8 flat head woodscrews to mount the sanding block to the wooden spacer block. Six holes were punched through the aluminum sheet and six #8 sheet metal screws were used to attach, on center, the aluminum sheet to the side of the wooden spacer block opposite to the rubber sanding block. Clamping the bent ends of the aluminum sheet into the electric sander's paper clamps, and mounting a piece of wet-dry sand paper on the curved-face rubber sanding block left the assembly ready to use finishing the outer surface of the volute between the volute stiffening rings. The first aluminum sheet did crack at one point in the finishing process, and had to be replaced.

[inbetweener] [inbetweener] [inbetweener] [inbetweener] [inbetweener] [inbetweener] [inbetweener] [inbetweener] [inbetweener] [inbetweener]

After the dry and wet sanding steps were completed, and sanding spoils washed off, the finish on the volute ring was very smooth, and also clear, but did not have the desirable luster of new acrylic plastic. A final shine was put on the volute by first polishing it with a muslin wheel mounted in an electric drill and #3 rub-on stick buffing compound, then cleaning off the remains of the #3 compound, and continuing polishing with #6 rub-on stick buffing compound, using a fresh muslin buffing wheel. Note in the first image below this paragraph how the buffing wheels are mounted on a length of threaded rod, separating the wheel by about eight inches from the drill chuck. This allowed working the muslin wheels into the corners between the volute face and the stiffening rings without interferrence from the drill chuck. When the compound buffing was completed, a final shine and polish of the volute surfaces was performed using spray-on acrylic polish and cleaner.

[final polish] [final polish]

The polishing process described above did a good job of restoring very damaged and glue ravaged acrylic plastic surfaces. The final results are quite acceptable. But, in all, I'd recommend making sure you have a good supply of masking tape before final assembly, and use it, so you won't have to take any required refinishing to the level that was necessary for this project.


The Key Is The Key:

(c.a., December 2007)

The key to flexibility of the Mark-II turbine as a test platform is its keys. Having an axle with key slots, and keyed runner discs and star washers, means, unlike the six-inch turbine, testing different runner disc styles and orientations doesn't require producing a complete new runner and axle assembly. Alternate runner parts are simply slipped on and off the axle as desired.

The axle assembly constructed for this project consists of a central 0.375" diameter US standard threaded rod to extend between the axle support uprights, having coupling nuts on either end that were machined to fit in bearings placed in inserts cut into the axle support. Threaded onto and centered on the 0.375" rod is a 0.825" diameter PVC plastic shaft with matching key slots cut at 180° from each other on the shaft. Runner discs and starwashers used with this shaft have 0.825" diameter center holes with key tabs to match the shaft key slots.

There are a couple of tricky bits to cutting a matching key slot pair in a shaft even with access to a slot cutter. Without the slot cutter, it becomes a bit more difficult. But, working in plastic, it is possible to do employing a Dremel™ tool with a few custom jigs and fixtures. The techniques used in this project to create the slotted shaft and tabbed runner discs are described in the subsections that follow.

Roughing It:

The rough blank for the central key slotted axle element was cut from a 2" thick by 6" wide PVC block as a 6" long strip approximately 1" wide. That strip was marked with diagonals on its small end to mark the small end center, and also marked with a center line along one of its 2" thick faces to use aligning the strip for center drilling with a long 0.3125" bit in a drill press.

[axle block] [axle block] [axle block] [axle block]

The Long And The Short Of It:

The central axle element rough cut block was drilled through with a long 0.3125" bit to allow it to be threaded with a US standard 0.375" tap. Coming up with a long 0.3125" drill bit is easy and they are inexpensive. Finding a long 0.375" tap is another story. They are not easy to find, and, if you can, they are expensive. I did try and make one from a short tap by welding a steel rod between the pieces after cutting the tap through its shaft. But, at the time I needed to do this my brother had absconded with the MIG welder, and with an oxy/acetylene rig, while I could produced good looking welds, it seemed like the tap steel adjacent to the welds became too brittle to trust. So, noticing that another tap was just about one half the length of the PVC block, I did the next best thing I could think of, and threaded the block as deep as possible from both ends.

[long and short] [axle block] [axle block]

Of course, threading a hole from both ends means the threads are very unlikely to be aligned all the way through the hole. But, there was method to my madness. Threading from both ends minimized the amount of material needed to be removed when using a piece of 0.375" threaded rod as a tap long enough to pass completely through the rough block; making the operation something more like cleaning up stripped threads through half the hole, than actually threading the block. A threaded rod is not a very good tap, but, grinding one end to a point and shaping that end with a round file so that it looked something like the end of a drill bit allowed the rod to be threaded all the way through the block, turning it with wrench against a set of double nuts.

[long tap rod] [long tap rod] [long tap rod] [long tap rod] [long tap rod]

Get A Round To It:

The rough PVC blank was trimmed with a hacksaw to just over 0.825" square, then the 0.375" threaded rod in its center was backed out until one end was about 1" below the end of the block, and a nut was tightened up against the PVC block on the other end of the 0.375" rod to fix the block on the rod. At that point the block was ready for mounting in a lathe for turning.

[trim block] [trim block] [trim block]

The 0.375" rod extending from the PVC block was chucked into a lathe, and a dead rest was run up into the open end of the threaded hole in the block. A thick motor oil additive was used for lubrication on the dead rest. With the block in place on the lathe, it was turned to 0.825" diameter, and trimmed to 5" length.

[turn block] [turn block]

Getting Around It:

To avoid damaging the surface of the rod when clamping it in a vice during construction, a set of soft jaws was fabricated. A 0.825" hole was drilled through a wooden block with 0.825" forstner bit for a close fit over the 0.825" rod. The block was then sawed in half down the length of the hole.

[clamp block] [clamp block] [clamp block] [clamp block]

The amount of material removed by sawing the block in half was sufficient to allow the halves to firmly clamp the rod in a vice, while preventing the vice jaws from damaging the surface of the rod. With the rod safely clamped in the vice, the 0.375" threaded rod in its center could be removed by backing it out with a wrench against a set of double nuts. With the 0.375" rod out of the way, a 0.825" die made short work of threading both ends of the 0.825" PVC rod.

[thread axle] [thread axle] [thread axle]

Once the ends of the 0.825" PVC rod were threaded, a length of 0.375" threaded steel rod was threaded through its center, using the soft jaws and a wrench and double nut set. This made the 0.825" PVC rod ready for slot cutting.

[short rod] [short rod]

On The Straight And Narrow:

Making a precise straight cut requires a guide. That is true whether cutting off the edge of a board, or cutting a slot in a rod. Cutting a slot in a rod has a few more complications than cutting off the edge of a board, because you can't simply clamp it down and "go for it."

The first consideration for slotting the rod was the width of the slot, since that would determine the dimensions of the guide. Here a 0.25" slot width was chosen, because I had a sharp 0.25" Dremel™ straight router bit and also some accurate thickness 0.25" aluminum bar material.

[slot fixture]

With the slot size chosen the next issue was how to center the rod under the cutter. Making a guide for the Dremel™ tool is not a problem. In fact, most of that work was already done in making the arc-cutting jig used in constructing the six-inch turbine. Adding a piece of aluminum angle material to either side of the arc-cutting jig will make it ready to slide down a guide and cut a slot. Rather than start with making the cutter ready to slide and trying to center the rod under the prepared cutter, its much easier to start from the middle and work out to the cutter guide.

The basic form of the slot cutting jig is two parallel, precise cut hardwood strips screwed to the face of a precise cut hardwood board, forming two guide rails for the cutter to slide down and the rod to sit between. Centering the cutter between the rails is accomplished geometrically, not by measuring, so, the exact spacing between the rails is not important so long as they are far enough apart to contain the 0.825" PVC rod. With that in mind, two precise cut 0.5" thick by 1.5" wide hardwood strips were cut 5.5" long to form the guide rails, and, two more cut approximately 4.5" long. These four strips were clamped together by their wide faces, with the longer wood pieces on the outside of the stack, and a piece of 0.25" aluminum bar in the middle. This arrangement places the 0.25" bar exactly centered between the outer rails. The assembly was centered on and clamped to an 8" long by 3.5" wide by 0.75" thick piece of hardwood, and #8 flat head wood screws used to attach the outer strips to the 3.5" wide base piece. With the guide rails in place, the inner strips can be used as a guide for centering the cutter in the jig, then removed to allow the 0.825" rod to be set in place and the slots cut.

[slot fixture] [slot fixture] [slot fixture] [slot fixture] [slot fixture] [slot fixture] [slot fixture]

With the guide rails in place, and the Dremel™ tool mounted on the arc cutting jig, the Dremel™ tool cutter can be centered between the guide rails. Since the 0.25" aluminum bar material is not as wide as the 0.5" thick hardwood spacer pieces, when the spacers and aluminum bar are in place between the guide rails, there is a 0.25" gap formed exactly centered between the guide rails. Setting the arc cutter jig on top of the guide rails, with the cutter in the 0.25" gap turned so that it touches both sides of the gap, centers the cutter between the guide rails. Clamping aluminum angle material lightly to the guide rails, then marking, drilling and attaching them through preexisting threaded holes in the arc cutter jig base completes the cutter alignment.

[slot jig] [slot jig] [slot jig] [slot jig] [slot jig] [slot jig]

Centering the 0.825" PVC rod between the jig guide rails becomes the next problem, and, once again, geometry provides the solution. If two parallel rods are set close enough together so that a third rod cannot pass between them, then laying the third rod on top of the two parallel rods places the center line of the third rod exactly in the middle between the center lines of the parallel rods. So, two 0.5" diameter steel rods were set between the slot cutting jig guide rails, and the 0.825" set on top of them, unavoidably centering the 0.825" rod between the guide rails.

[slot fixture] [slot fixture]

To provide secure, centered mounting for the 0.825" rod in the slot cutting jig, two pieces of 0.125" thick by 0.75" wide steel bar were cut to span between the ends of the slot cutting jig guide rails, and slotted to fit the 0.375" rod threaded through the center of the 0.825" rod. With the steel bar pieces held in place, the positions of predrilled screw holes in the steel bar pieces were marked on the ends of the jig guide rails, pilot holes drilled, and the bar pieces screwed in place.

[slot fixture] [slot fixture] [slot fixture] [slot fixture] [slot fixture] [slot fixture]

One of the slotted steel bar pieces was installed with its slot facing upwards, to allow passage of the cutter when using the jig, and the other was installed with its slot facing downwards to allow the 0.5" steel rods to be removed and also provide space for alignment pieces that will be used to set the second slot cut exactly 180° around the 0.825" rod from the first cut. By lightly clamping the 0.825" rod down onto the 0.5" rods, and using nuts on the ends of the 0.375" rod, the 0.825" rod can be firmly attached, on center, between the slot cutting jig guide rails by tightening the nuts against the steel bar pieces.

[slot fixture] [slot fixture] [slot fixture] [slot fixture] [slot fixture]

To keep the guide rails stable during use, a small block was attached to the bottom on the jig base so the base could be set squarely on top of a large vice, and also clamped into the vice via the small block.

[slot fixture] [slot fixture]

Serendipitously, the face of the retaining nut on the 0.375" shaft at the upward slot steel bar end of the key-slot cutting jig was at a good height to define the depth of key slot cut in the 0.825" PVC rod. To provide clearance for the cutter over the nut, a 0.022" feeler gauge was laid on the nut face and the height of the cutter adjusted to touch the face of the gauge with the cutter jig in place on the guide rails.

[set slot depth]

With the 0.825" rod centered and firmly attached between the slot cutter gig guide rails, and the cutter height set, the cutter was turned on, and slid along the guide rails, making the first key slot.

[slot one]

To make the second slot exactly 180° around the 0.825" rod from the first slot, two pieces of the 0.5" thick hardwood strips were cut narrow enough to slide under downward facing slot steel bar, and, similarly a piece of 0.25" aluminum bar was cut, making sure the narrow end of the bar was at the correct height to slip into the first cut slot when the 0.825" rod was rotated 180° in the the slot cutting jig. Using the 0.5" hardwood strips to center the 0.25" bar between the guide rails, and sliding the bar piece into the first slot guarantees the second slot will be cut 180° from the first slot. With the rod properly positioned, and the retaining nuts tightened down, the second key slot was cut.

[align slot] [align slot] [slot two] [both slots]

Keep It In Line:

Having an axle with key slots is only half the problem solved. To use the axle a way of employing the slots to lock items to rotate on the axle is needed. In these kinds of applications one often sees slots cut in the center holes of an item to rotate that line up with the key slots in the axle. A square metal bar (the key) is set in the axle slot, and the item to rotate slipped over the both the axle and the key bars.

The key bar method would work fine for Mark-II turbine runner discs and starwashers. But, since the runner elements are held in place by spacers and nuts from either end of the axle, that would mean having to not just adjust spacer lengths, but also cutting custom length key bars following each modification to the runner element stack to allow the axle nuts and spacers to compress the stack sufficiently for the turbine to function properly.

Adjusting spacers is pretty easy to do. Cutting key bars to the correct length to allow proper runner stack compression isn't "difficult," but more problematic for quick changes. So, rather than use key bars and slots, the choice was made to put tabs extending into the center hole of runner elements to align with the axle key slots. That way, the runner elements slipped on the the axle are immediately stopped from spinning on the axle and only need to be compressed together with spacers and nuts on the axle for the turbine to function, regardless of the width of the runner element stack.

Given the two runner discs used for alignment during initial construction had predrilled center holes, the easiest way to provide them with tabs was to first cut slots in the center holes to align with the 0.825" shaft key slots, then glue strips of material into the center hole slots to form the tabs to slip into the axle slots.

Just as much care towards alignment is necessary for cutting tab slots in the runner discs as was used when cutting key slots in the 0.825" axle piece. The first step was to enlarge the existing 0.5" diameter holes to 0.825" to allow the runner discs to slip over the 0.825" PVC axle piece. That meant centering the existing 0.5" holes under the chuck on a drill press. Centering was accomplished by placing a runner disc on a board sitting on the drill press table, chucking a 0.5" diameter forstner into the press, extending the press to drop the bit through the hole in the disc, and clamping the board and disc to the drill press table. With the disc now centered under the chuck, the 0.5" bit was replaced with a 0.825" bit, and the disc center hole enlarged with the larger bit.

[align runner hole] [align runner hole] [align runner hole]

With proper diameter, centered holes drilled in the runner discs, the next step was to center the Dremel™ tool router cutter in the predrilled holes in the runners discs. An alignment fixture was turned from a block of PVC material by cutting it to 0.825" diameter for about 0.5" of its length, cut increasing the cut to create a 0.25" diameter stob about 0.75" inches long extending from center of the face of the 0.825" diameter section.

[key tab alignment] [key tab alignment] [key tab alignment] [key tab alignment] [key tab alignment]

Using a 2.25" diameter forstner bit to cut a pocket about 0.125" deep in the face of a board large enough to support a runner disc, then drilling a 0.25" hole in the center of the pocket provided a jig for cutting tab slots aligned at 180° in the runner disc center holes using the Dremel™ tool router. The pocket was cut to clear wood from the face of the board so the router cutter only had to cut runner disc plastic, and not clear wood under the tab slot cuts as well. Inserting the 0.25" stob on the alignment fixture then dropping a runner disc center hole over the 0.825" portion of the alignment fixture centers the runner disc around the 0.25" hole in the board. Clamping the disc to the board keeps the disc centered after the alignment fixture is removed.

[key tab alignment] [key tab alignment] [key tab alignment]

Setting the router on the clamped down runner disc and extending its 0.25" cutter into the 0.25" hole in the board the disc is clamped to centers the router cutter in the center of the runner disc center hole. Placing a piece of aluminum angle material against the flat face of the router and clamping the angle material to the board and runner disc stack provides a guide allowing the router to ride along with its cutter exactly centered over the runner center hole and cut tab slots on center and 180° apart in the runner center hole. Retracting the cutter so its bottom was above the face of the board pocket but below the bottom face of the clamped runner disc, the router was turned on and tab slots were cut extending about 0.375" into the runner disc. Removing the runner disc from the alignment and guide assembly and slipping its center hole over the 0.825" portion of the axle assembly showed the alignment of the tab slots with the key slots.

[key tab alignment] [key tab alignment] [key tab alignment] [key tab alignment] [key tab alignment]

To cut tab slots in the second runner disc the PVC alignment fixture was reinserted in the 0.25" hole in the cutting board, and the second disc was placed on the alignment fixture followed by the disc with its tab slots already cut. The two discs were fixed relative to each other by putting a screw through one of their mutual assembly screw hole sets, and, because there was a convenient pocket in the cutting board near another of the assembly hole pairs the discs were rotated slightly on the alignment fixture to allow the shank of a drill bit of the same diameter as the assembly holes to be dropped through the second hole set over the pocket for additional registration control.

With both runner discs centered, linked together, and clamped down on the cutting board, the aluminum angle piece was set in place for guiding the router again. But, this time, besides centering the cutter in the 0.25" hole in the cutting board the the router was slid back and forth along the angle piece and the position of the piece adjusted until the cutter moved smoothly into both tab slots in the upper runner disc, taking care that the full 0.25" diameter portion of the cutter contacted both sides of the tab slots. With this operation completed, the assembly was properly aligned to cut tabs in the lower runner disc that match the positions of the tabs already cut in the upper disc. Without removing the upper disc, the cutter was lowered to allow it to cut the lower runner disc tab slots. Because of how the discs were registered together, not only are the tab slots in both discs aligned, but, so are the assembly holes in both discs relative to the tab slots.

[key tab alignment] [key tab alignment] [key tab alignment] [key tab alignment] [key tab alignment]

Running A Tab:

Key tab material for the runner discs was cut using a Dremel™ tool router in a jig constructed for removing an accurate 0.25" wide strip (the width of the tab slots) from the edge of a piece of 0.091" thick acrylic plastic sheet. The jig was assembled from precise cut hardwood strips on a base piece such that a router guide strip was placed 0.5" from, and parallel to, a router platform piece. Two strips of hardwood were cut 0.25" thick to drop into the 0.5" gap between the router guide strip and the router platform piece to create a secondary router guide spaced 0.25" from the first guide. The 0.25" strips were cut on a table saw, using a piece of 0.25" aluminum bar material to space the saw blade from the saw guide. Cutting thin strips from already thin strips is dangerous. To avoid cutting off your fingers, use guide blocks and push sticks.

[key slot fixture] [key slot fixture] [key slot fixture] [key slot fixture] [key slot fixture] [key fixture]

With the guides completed, a clamp strip was screwed to the bottom of the base piece to allow mounting the jig securely on top of a large vice. Before using the jig to cut plastic, the router was run down the support platform against both guides to relieve about 0.125" of wood from under the cutter trim lines.

[key fixture] [key fixture] [key fixture]

Counter sunk holes were drilled in two corners of the piece of plastic to be trimmed for the key tab strips, and the plastic mounted on the router support piece with flat head wood screws set deeply enough so the router could slide over the heads without interference. The edge of the plastic piece was set so its edge closest to the fixed router guide was past the edge of the cutter trim line closest to the fixed router guide. Making a cut first against the fixed guide, then installing and making another cut against the secondary guide provided a plastic strip exactly the width of the slots in the 0.825" axle piece.

[key fixture] [key fixture] [key fixture] [key fixture] [key fixture]

Four tabs for inserting into the key tab slots in the runner discs were made by grinding the end of the strip to fit the rounded portion of the key tab slots and trimming off a length of the strip sufficient to reach into the key slots in the 0.825" axle piece. The rounded and trimmed tab pieces were then glued into the tab slots.

[key tab alignment] [key tab alignment] [key tab alignment] [key tab alignment]

It turned out that the inside diameter of a section of so-called 3/4" PVC pipe was the correct size to fit (a bit loosely) over the 0.825" diameter PVC section of the turbine runner axle assembly. So, three spacers were cut from the pipe to position the key tabbed runner discs in the center of the volute when the axle was assembled and installed in the turbine axle support uprights.

[runner spacers] [runner spacers] [runner spacers] [runner spacers]

This Has Some Bearing:

Rather than use the bushings for the keyed axle assembly, ball bearings with a 0.5" inside diameter and a 1.125" outside diameter were used to allow the keyed runner assembly to spin as freely as possible.


The same basic technique use to enlarge center holes in the runner discs was employed to create centered bearing pockets in the the uprights. With the turbine volute ring removed, in turn on each upright, an electric hand-drill angle-boring jig with the angle set to 90° and a 0.5" forstner bit in its chuck was c-clamped to the volute side of the uprights such that the 0.5" bit could be smoothly extended through the 0.5" hole in the uprights, (using cardboard and wooden blocks to protect the finished surfaces of the uprights from the jig face and c-clamps). With the boring jig thus centered over the hole in an upright, the 0.5" bit was changed out for a 1.125" bit, and a pocket cut into the upright to a depth matching the thickness of the bearings. Similarly, on the outside of both uprights, the remaining length of 0.5" diameter hole was expanded to 0.75" in diameter to allow the ends of the keyed shaft to spin freely in their bearings.

[bearing pocket] [bearing pocket] [bearing pocket] [bearing pocket]

Two 2" long 0.375 US standard thread coupling nuts were used to create bearing surfaces for the keyed axle assembly. The nuts were chucked into a lathe, and about 1.5" of their length turned down to 0.5" diameter, then taken down farther with emery paper and shined with crocus cloth so that the 0.5" inside diameter bearings would slip smoothly over them.

[bearing nut] [bearing nut] [bearing nut]

Get Ready:

To prepare for final assembly of the Mark-II turbine, the center holes in the volute end plates were enlarged from 0.75" to 2.25" using the same small bit centering to large bit cutting alignment process as before. This gives clearance for the ends of the 0.825" diameter PVC segment of the keyed axle assembly and its runner assembly clamping nuts.

[side plate vent] [side plate vent]

Then, the keyed runner components were assembled in their final configuration. The full length 0.375" US standard thread central axle rod was threaded through the 0.825" diameter PVC section by clamping the PVC section in a vice using the previously cut soft jaws, then starting the rod in the threaded hole in the PVC section and turning a wrench against double nuts on the rod, until the PVC section was centered on the threaded rod. Finally one of the partially turned coupling nuts was threaded onto each end of the central threaded rod, with their turned ends pointed away from the PVC section, and 0.5" inside diameter locking collars slipped onto the coupling nuts.

[axle assembly] [axle assembly] [axle assembly] [axle assembly]

To insert the axle into the axle support uprights, one of the coupling nuts is threaded about half way up the 0.375" threaded rod towards the PVC section of the keyed axle assembly to allow that end of the rod to be passed through the 0.5" hole in the bearing in its upright sufficiently deep to allow the coupling nut on the other end of the threaded rod to be aligned with and inserted into the bearing in its upright. The coupling nut that was threaded towards the PVC section is then threaded back down the rod until it slides into its bearing.

[axle assembly] [axle assembly] [axle assembly] [axle assembly]

The Final Play:

For final assembly of the Mark-II turbine, first, one of the volute end plates is leaned against the volute side of one of the axle support uprights. On one end of the keyed axle assembly central threaded rod a regular 0.375" US standard nut is run up the rod followed by one of the partially turned coupling nuts, (turned end facing away from the PVC key-slot rod), until both are near the PVC key-slot rod, and a 0.825" US standard nut is threaded onto the threads on that end of the PVC rod. Then, a 0.5" locking collar is slipped over the coupling nut near the PVC rod, and the exposed threaded rod is passed through the center hole of the end plate leaning against the upright, and also through the 0.5" hole in the bearing in the bearing pocket in the upright. After this the PVC pipe spacers and runner discs are slid, in order, over the other end of the threaded rod and onto the PVC rod, followed by a 0.825" US standard thread nut turned onto the threads on that end of the PVC rod. This is followed by the second volute end plate being slipped over the end of the axle. On the end of the central threaded rod the runner pieces were slipped over, a regular US standard 0.375" is threaded onto rod followed by the second partially turned coupling nut, (turned end away from the PVC rod), and a 0.5" locking collar is slipped onto the coupling nut. That coupling nut is inserted into its bearing. The coupling nut near the PVC rod is then turned down its end of the threaded rod and into its bearing. With the axle now properly supported in the bearings, the 0.825" nuts on the ends of the PVC rod are tightened to compress the spacers and center the runner discs on the PVC rod. With the runner discs in place, the volute end plate brass washers and screws are installed. The regular nuts on the threaded rod inside of the coupling nuts are turned down the threaded rod until they contact the coupling nuts, and the regular nut and coupling nut pairs are tightened together, double-nut fashion, to retain the coupling nuts on the threaded shaft. Finally, the locking collars are adjusted to take the play out of the shaft by sliding them up to the bearing faces and tightening them down.

[final axle assembly] [final axle assembly] [final axle assembly] [final axle assembly] [final axle assembly] [final axle assembly]


Powered Puff Whirls:

(c.a., November 2006)

[amp nozzle fit]

[air amp fitting mod] [air amp fitting mod] [air amp fitting mod] [air amp fitting mod]

(c.a., December 2006)

[air amp retainer] [air amp retainer] [air amp retainer] [air amp retainer] [air amp retainer] [air amp retainer] [air amp retainer]

[air amp spacers] [air amp spacers] [air amp spacers]

(c.a., September 2007)

[air amp fitting mod] [air amp fitting mod]

[air amp o-ring] [air amp o-ring] [air amp o-ring] [air amp o-ring]

[air amp new nozzle]

Do You Believe In Magic?:

Air Amp 2:


Wax On Wax Off:

(c.a., February 2007)

[implements] [implements] [implements]

[flat sheets] [flat sheets]

[wrap over] [wrap over] [wrap over] [wrap over] [wrap over]

[add bottom] [add bottom] [add bottom]

[square up] [square up]

[clean up]

(c.a., March 2007)

[cast it] [cast it] [cast it]

[polish it] [polish it] [polish it] [polish it] [polish it] [polish it] [polish it] [polish it]

[heat stress] [heat stress]

Any Way You Slice It:

Could I Have Than As A Wrap?:


A Clear Investment:

(c.a., June 2007)

[box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form] [box form]

[templates] [templates] [templates]

(c.a., July 2007)


[wax blocks] [wax blocks] [wax blocks] [wax blocks] [wax blocks] [wax blocks]

(c.a., August 2007)

[shape main] [shape main] [shape main] [shape main] [shape main] [shape main] [shape main] [shape main] [shape main] [shape main] [shape main] [shape main] [shape main]

[shape inlet] [shape inlet] [shape inlet] [shape inlet] [shape inlet]

[final core]

[end plug] [end plug] [end plug] [end plug]

[wax box] [wax box] [wax box] [wax box]

[mold assembly] [mold assembly] [mold assembly] [mold assembly]


[boil out] [boil out] [boil out] [boil out]

[clean up] [clean up] [clean up] [clean up] [clean up]

[inlet insert] [inlet insert] [inlet insert] [inlet insert] [inlet insert]

[preliminary mount] [preliminary mount] [preliminary mount] [preliminary mount] [preliminary mount] [preliminary mount] [preliminary mount]

(c.a., September 2007)

[final mount] [final mount] [final mount] [final mount] [final mount] [final mount]

An Artist's Conception:

A Tough Scrape:


Give It To Me Straight:

(c.a., September 2007)

[straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe] [straight inlet pipe]

Straight One:

Straight Two:



(Clicking reference numbers here takes you to the text location of the reference.)

[1] Heimann, Erich H., 1975. Do it yourself with plastics. Mills & Boon Limited.


Last updated 03August2008
Alan Swithenbank, alans@cuervo.stanford.edu