Nathan, So if I understand correctly, you have a pair of bevel gears which transmit drive to a straight cut pinion which is meshed with a straight rack.  One of the bevel gears shares a shaft with the pinion to transmit the torque. Using conventional gear cutting manufacturing, all the gears would be made separately then fitted to shafts with keys or splines, keys are intended to shear if the drive system stalls or seizes. You can make the bevel and straight cut pinions separately then fasten them together so they rotate on the shaft, depending on your application you might use real metal ball/roller bearings. Ideally the bevel and pinion would be similar diameters, or the straight cut pinion larger. The geometry of your application will determine the overall gear dimensions, then you need gear ratios and tooth counts which fit the space and the transmitted load. Most of the OpenSCAD gear applications use Module (confusingly), the alternative is Circular Pitch, which I find easier to use. These might help.. https://www.engineersedge.com/gear_formula.htm https://www.youtube.com/watch?v=8bml2pK6Ra0 https://geargenerator.com/#200,200,100,6,1,3,0,4,1,8,2,4,27,-90,0,0,0,0,0,0,16,4,4,27,-60,0,0,0,0,1,1,12,1,12,20,-60,0,0,0,0,2,0,60,5,12,20,0,1,0,0,0,0,0,3,-515 This is really cool [IMO] https://geargenerator.com/beta, you can see the effect of reducing the module to make the teeth smaller. Unfortunately neither do bevel gears, but it will help with the variables you need to feed into the OpenSCAD gear creating code. Roger.

Seems like for 3d printing if you can print your pinion joined to your bevel gear that would be much better than trying to fuss with some key system. But that might not be practical. Note that BOSL2 allows you to specify gears by circular pitch, module or diametral pitch. When you read the gear literature, it is all based on module. On Tue, Oct 28, 2025 at 7:08 AM Roger Whiteley via Discuss < discuss@lists.openscad.org> wrote: > Nathan, > > So if I understand correctly, you have a pair of bevel gears which > transmit drive to a straight cut pinion which is meshed with a straight > rack. One of the bevel gears shares a shaft with the pinion to transmit > the torque. > > Using conventional gear cutting manufacturing, all the gears would be > made separately then fitted to shafts with keys or splines, keys are > intended to shear if the drive system stalls or seizes. > > You can make the bevel and straight cut pinions separately then fasten > them together so they rotate on the shaft, depending on your application > you might use real metal ball/roller bearings. Ideally the bevel and > pinion would be similar diameters, or the straight cut pinion larger. > > The geometry of your application will determine the overall gear > dimensions, then you need gear ratios and tooth counts which fit the > space and the transmitted load. > > Most of the OpenSCAD gear applications use Module (confusingly), the > alternative is Circular Pitch, which I find easier to use. > > These might help.. > > https://www.engineersedge.com/gear_formula.htm > > https://www.youtube.com/watch?v=8bml2pK6Ra0 > > > https://geargenerator.com/#200,200,100,6,1,3,0,4,1,8,2,4,27,-90,0,0,0,0,0,0,16,4,4,27,-60,0,0,0,0,1,1,12,1,12,20,-60,0,0,0,0,2,0,60,5,12,20,0,1,0,0,0,0,0,3,-515 > > This is really cool [IMO] https://geargenerator.com/beta, you can see > the effect of reducing the module to make the teeth smaller. > Unfortunately neither do bevel gears, but it will help with the > variables you need to feed into the OpenSCAD gear creating code. > > Roger. > > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org