Chainring bolt replacement PROTOTYPE for single chainring

cults3d

Disclaimer: This is a work in progress and at this point is a prototype to see if it is feasible. I'll be testing this on my own with the bike mounted in a trainer, so if it breaks, I'm not as likely to really hurt myself. If you try this, understand that it's untested and might be a very bad idea. If this breaks while you're riding, it could go very badly for you. *Updates: * 25 Jan 2018 - Broke one of the v1 designs a couple weeks ago, the edge under the bolt head sheared off. This morning while doing some maximum watt sprints, I hamfisted a shift and threw the chain, breaking two more of the v1 designs. Since the first breakage, I did redesign and have a v2 I'm working on that seems to be stronger, but it should be emphasized again that this is probably a really bad idea and I'm just doing this to see how far simple FDM printed parts can be pushed. I'm running these on my indoor trainer bike so if they fail the odds of me crashing are pretty low. Here's a concept for a replacement for a single chainring mounting nut that uses a standard M5x0.8mm screw. I've got a bunch of disk brake mounting screws on hand, so I used those, but any normal M5x0.8 screw can be used, as long as it is at least 8mm. There are two parts to each, the chainring nut which is threaded for the M5x0.8 screw, and the washer which fits on the other side of the chainring and under the head of the M5 screw. To assemble, the nut goes in from the backside of the crank, and the screw and washer go on from the other side. As long as your threads are clean, it should thread in without too much trouble, and I was able to hold the nut in place with just hand pressure, vs. having to use the screwdriver slot in the back. I'll be building this bike up soon and will be mounting it on a trainer for strength testing. I'm pretty big and capable of over 1300W for short sprints, so should be able to really test this design. FreeCAD is supposed to have a BOLTS library for standard threads, but it's offline and looking at the github issue, I'm guessing there's not a huge push to bring it back. To get around this, I downloaded the STEP file of an M5 high nut from McMaster-Carr which is wonderfully useful.