ME325: Making Multiples teaches students to use the Product Realization Lab's 50-ton Arburg vertical injection molding machine. We progressed through several smaller projects, including poker chips and personal tokens, before spending the last 5 weeks of the quarter on open-ended final projects. For my final project, I made "trigger keepers" for climbing cams. Cams are mechanical pieces of climbing protection that are placed in cracks to create anchors or hold falls. Large cams are cumbersome to store or carry with the lobes extended, so some new cams come with trigger keepers that hold them shut while not in use. My trigger keepers are designed to add the same functionality to older cams or cams from other companies.
I began by creating laser-cut and 3D printed prototypes to figure out what shape provided the best functionality and ergonomics. I settled on a "claw" shape that's attached to the cam's trigger bar with a string. The device can be disengaged quickly with one hand, which is important for actual climbing use.
The next challenge was to mold a part with similar geometry. The footprint and depth of the mold cavity were constrained by the size of inserts compatible with our molding machine's master unit die. I ended up orienting the parts vertically in the mold, letting me produce 4 parts at a time within the insert's 3x5" footprint. The mold has a nonplanar parting surface with several shutoffs to create the "hooks" on either end. I used tapered end mills to quickly create the angled shutoff surfaces. Each side took about 2 hours to machine on one of the PRL's VF2-SS CNC mills.
It took a few iterations to get the mold to shut off properly. Once that was done, it was fairly quick to produce some ejector pins and to dial in the correct parameters on the molding machine. I used ABS, which was the most rigid of the plastics available. In my final production run I made over 200 of my parts, with one machine cycle producing 4 parts in about a minute.
As I write this about 2 months later, I've added trigger keepers to all of my large cams and have used them on many outdoor climbs. I've given several sets to friends and to people I've run into at the crag. If I have the chance to iterate one more time, I think I can reshape the hooks so that they grab a little more firmly, but overall I'm happy to have created a novel and useful (but niche) product.
(Click to return to project list)
