The gears are mod0.8. 40, 20, 12, 10 and 8 teeth. I cut the bevel gears and the pinions out of 3mm brass sheet stock while the larger wheels are cut out of 0.7mm brass stock. (Why this modulo? That was the smallest gear family my prusa 3d printer could print reliably, and i guess i just stuck with it as i transfered to cutting brass) (Why this stock thicknesses? That is what amazon had in next day delivery :))
I design the mechanism and create the cutting toolpaths in fusion 360. The paths are 2d profile cuts for the straight pinnions and wheels, and 3d profile cuts for the bevel gears. For the bevel gears I have a “roughing pass” with a 1.7mm bit followed by two passes with a 0.8mm bit. This seems to be needed otherwise as the tiny bit steps “down and out” it encounters too much depth on the “outside” of the cut. At least that is how I explain it. What is certain that when i tried to cut the bevel gears with a single pass the 0.8mm bit broke all the time, and with this strategy I can cut all four of my bevel gears with the same two cutters. :) The pinions and wheels with straight walls I cut with a single pass.
I take 0.1mm deep cuts with 45mm/min feed, altough truth to be told I have tried 250mm/min feeds also and that seemed to be fine too. 350mm/min broke the bit too often.
I run the spindle at a constant max speed, which I have measured to be 27000rpm unloaded. Haven’t measured during cutting but somehow I doubt the dewalt with all its 900W slows down at allwith these tiny bits and cuts.
For work holding I use the following “sandwitch”: a 6mm thick aluminum plate is toe clamped to the bed of the CNC. There is blue painters masking tape glued on the aluminium waste board, super glue on that and the brass stock is held on by that super glue.
I start the cuts 0.3mm above the stock and finish it 0.3mm bellow. I probe the stock’s surface, back the bit up until it breaks the contact and zero it there. The gears I cut are small enough that i don’t seem to benefit much from z-scanning the surface of the stock. I use Universal GCode Sender to send the gcode generated by fusion.
Sorry for the lot of detail, just wrote what I wished have known a few months ago. Let me know if there is anything else you are currious about.
It's fun reading what other people are using these for in practice, and not just the sunny days version. If I ever try cutting brass with this level of detail and scale, this is exactly the kind of thing I'd want to read first.
I look forward to seeing your next project come to life!
Incidentally, your workholding is called a paper joint in woodworking, and is used to make split turnings and sometimes to attach clamping cauls :-)
