Well, I was going to wait and post the making of the bevel gears for the Shay all in one post, but it turned out I did not have any brass large enough diameter for the ones attached to the wheels so had to order some more (found a chunk of 1-5/8" bar as a drop at a commercial supplier, it should be here later today according to the tracking).
So, I got started with the smaller gears, a 20-tooth gear at 26.57 degrees. These are being done with a 44 tooth-range cutter, module 0.7. First up was to turn the blank on the lathe, with the bevel done with the compound slide
and the rest done with the normal slide. Since the teeth will intersect the post of the gear, the gear is first made with the post on the large side, which later on will be turned off after a new post is hard soldered on the small side of the gear.
With the blank turned in the end of a brass rod, the chuck was moved over to the rotary table, which was set at a 26.57 degree angle to the mill bed. Since that did not leave enough travel on the bed, I got out the heavy plywood extension that I made several years ago for cutting large clock gears.
The teeth were cut in three passes, one normal pass to cut the slot between all the teeth, then two more passes to take a slight wedge off the side of the large end of each tooth to give it the final shape - this is needed since the teeth and the gaps between them need to be tapered on a bevel gear, and the cutter will only do a parallel-sided gap in a single pass. I used the formulas from Ivan Law's book on gear cutting (with the correction from Sine to Cosine that I learned from other's posts - that saved the day!). I tried to get photos showing the process, but they did not come out well enough to show - will try again with the larger gears, hope they show the difference between passes.
As each gear was completed, it was cut off the bar, and the process started again for the next one - 4 gears needed in total.
Once all the gears were cut (they mesh very well with each other, so that is a hopeful sign I did it right, will know for sure once the large gears are made) it was necessary to make a new post for the small end. The posts were turned to the final diameter, with a smaller end that fit snug into the holes in the gears. They were then silver soldered in place.
After soldering, the gears were chucked up in the 4-jaw, and trued using the original post. They were then redrilled through the new post, and the old post turned off. Again, this was needed since the final post coming out of the small end of the gears would have been in the way of the gear cutter.
Once the gears were done, a setscrew was drilled/tapped into the post to hold them on the line shafts. Once the trucks are done, the positions of the gears will be adjusted to mesh well, then the posts will be cross drilled for final pins - the setscrews are just to allow that adjustment before pinning.
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