Pinion gear; take 4; no juice

I attempted to cut a pinion gear again, with no luck.

I’m using a 24 pitch 14.5o involute gear cutter on a Sherline gear cutting arbor. I want to cut a 12 tooth gear. I turn a 3/4″ round bar stock down to 37/64.

(Teeth + 2) / pitch = Outer Diameter
(12 + 2) / 24 = .5833 ~ 37/64

I then transfer the chuck to the rotary table. I lower the headstock so that the bottom of the gear cutter touches the blank. I then divide the cutter height by 2, and lower the headstock by that much:
Cutter width = 15/64, half = 1/8.

The radius of the blank is 19/64.

And somewhere I’m off by a 1/64 of an inch which blows the tooth geometry…

I much be sloppy somewhere and am just missing it.


I’ve always loved gears. Who doesn’t? Since getting the lathe and mill, I couldn’t wait to try to make gears. Slowly, over the last year, I’ve acquired the components to make a gear – from the rotary table, the angle plate, the gear cutters, the arbor, the threading attachment so I could make a gear cutting mandrel… I was finally able to make my first set of gears:

These will eventually be the cord engagement gears. I need to mill the 1/8 grove which will capture the cord.

I had much less luck with the smaller pinion gear:

As you can see the teeth aren’t formed correctly. This is actually the 3rd attempt. On my first attempt I accidentally attempted to cut 24 teeth instead of the 13 I was shooting for. I decided the second attempt to cut 12 teeth because it divided cleanly, but forgot to adjust the blank diameter. The third attempt, it looks like I forgot to center the cutter, so it is off… Too late to start a new blank, so left for another night.

For kicks, here’s my gear cutting setup:

Captured Gear Drive

During the Seattle robotics meeting, I ‘crossed the streams’ (reverse polarity) and destroyed the motor controller (and presumably the motor, don’t want to take changes). Given that I wanted to standardize on the 12v motors I was using for the Axis, this seemed like a good time to incorporate this motor into the extruder. 

While building the new motor mount, I decided to look into a different type of extruder drive, similar to the pinch pulley, but built with gears. Two drive gears have a 1/8 channel milled into them. The gears with the channel ‘capture’ and hold the plastic cord. I wasn’t sure how long the urethane pulley would last, so this is an experiment.