Another few hours in the workshop, and I made the spur gear which transmits power to the dredger bucket chain.
I chose bronze, because 1. It will not rust 2. It machines fairly easily 3. I had some in the correct size!
I did think about whether to CNC mill the gear, or make it on my lathe and form the teeth with a custom built cutter. In the end, I decided to CNC mill the entire part. The plans called for a tooth shape which looked like an Acme threaded part. I decided that Trevithick would NOT have made it like that, nor would he have known about pressure angles, and parabolic tooth shapes, so I winged it and drew a shape on the CAD which was a bit between both.
Roughing the shape was with a 6mm 4 flute carbide cutter.
And finishing, to impart the fine fillets, was with a 3mm carbide cutter, taking 1mm depth bites. I broke one, but the next one, new, finished the job intact.
And here is the gear, still attached to the bronze rod. Now, how to detach it?
Hey, no aliens! But watch this...