Sprocket wrench for Gates Carbon Drive

thingiverse

Sprocket wrench for Gates Carbon Drive, a carbon belt drivetrain for bicycles Note: After having used this wrench a few times, I'm not so sure this is a good design. Because it only engages the teeth on one side of the sprocket, it has a tendency to slip off. That's super annoying. Also, the short handle makes it really difficult to apply enough torque. I usually wrap a piece of nylon webbing around the handle and attach it to the rim to prevent it from turning, but it can still slip off. The wrench has been used successfully to apply 30 Nm of tourque on a 20t sprocket. Enough to meet the specs on Rohloff's locking sprocket carrier. The OpenSCAD file provides a parameter to change the number of teeth, but this has not been tested as I only have 20t available. YMMV. It is recommended that you first do a test print to make sure it fits your sprocket. Different 3D printers, settings, filaments and sprocket wear all play a significant role. Include only the teeth and the rim, no handle and only a couple of layers thick. See the comments for hints. If it fits, it fits - Yay! Otherwise you'll have to fudge around with the parameters. The handle is a bit short, but this allows the whole wrench to fit a 140x140 mm build plate. You should increase totalSize if you have a larger build plate to make the wrench easier to hold on to. There's a surprising amount of pitfalls for making such a tool. Many prototyping iterations were either too tight or too loose. Some of the belt and sprocket dimensions were difficult to measure accurately and required some trial and error. You can also get the official wrench from Gates, but printing your own may be cheaper or more convenient. I needed one urgently and couldn't wait for shipping. As such, parts of the sketch are dirty code, but it turned out to work very well.