Chainring bolt replacement PROTOTYPE for single chainring

thingiverse

***Disclaimer:*** This work in progress is a prototype to test its feasibility, and it's currently being tested on my own bike mounted in a trainer. If it breaks, I'll likely only hurt myself, as the risk of injury is low. Understand that this untested design might be a very bad idea, and if it fails while you're riding, things could go badly for you. **Updates:** * **25 Jan 2018** - Broke one of the v1 designs two weeks ago when an edge under the bolt head sheared off. This morning, I threw the chain with a hamfisted shift, breaking two more v1 designs. Since the first breakage, I redesigned and now have a v2 that seems stronger, but it's still a bad idea to attempt this. I'm only doing this to see how far simple FDM printed parts can be pushed, and I'm running these on my indoor trainer bike so the odds of me crashing are low. Here's a concept for a replacement chainring mounting nut using a standard M5x0.8mm screw. Since I have disk brake mounting screws on hand, I used those, but any normal M5x0.8 screw can be used as long as it's at least 8mm. There are two parts to each: the chainring nut threaded for the M5x0.8 screw and the washer that fits under the head of the M5 screw on the other side of the chainring. 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 trouble, and I was able to hold the nut in place with just hand pressure. I'll be building this bike up soon and will mount it on a trainer for strength testing. I'm big enough to generate over 1300W for short sprints, so I can really test this design. FreeCAD supposedly has a BOLTS library for standard threads, but it's offline. To get around this, I downloaded the STEP file of an [M5 high nut](https://www.mcmaster.com/#90725A030) from [McMaster-Carr](https://www.mcmaster.com/), which is incredibly useful.