The hardest hurdle arrived right at the start: the first prototype off the FDM machine came out wafer thin, weak and warped, a white plastic test piece that plainly would not last. Rather than keep wrestling with filament, the maker, Deltahedra, changed course, sent the STEP file to PCBWay for stereolithography, and finally had the part CNC machined from 7075 aluminum alloy. That path from a failed print to a metal component is what makes this project worth studying.
The geometry was worked out in FreeCAD version 0.21 across five successive models, with the design broken into three parametric stages. Sizing came from the pitch circle diameter formula, matched to a chain pitch of 12.7 mm, and the mounting layout follows the 104 mm bolt circle standard with an 88 mm inner register. Digital calipers and a kitchen scale were both part of the measuring work.
Several details stand out. The model is parametrically adjustable from 40 to 50 teeth, so one file covers a wide spread of gearing. The finished ring came in at 97 grams, comfortably under the 100 to 110 gram target. It was gold anodized with chamfered edge accents, and in the real-world functional test it spun smoothly, with the tooth profile and structural rigidity handling dynamic forces well.
One piece stays open: the honeycomb pockets. How those were machined, and with what tooling, has not been laid out yet, and that seems like the most interesting remaining chapter for anyone hoping to repeat this build.
Project by Deltahedra. Watch it on their YouTube channel: