[Kevin Sevcik]

57 uses a tranny like this but with just 2 gears.

You could make it smaller if you went with a rather counter intuitive shifting pattern. Call 1 the biggest gear on your shifter. If you arrange the gears on the shifter as 2-1-3 instead of 3-2-1 then you could have all 3 gears next to each other. Then your whole assembly would just need to be 7 times the width of a gear plus some tolerances. Downside of course is that you'd have to go through your high gear to get between your two low gears. Or low between two highs depending on which side of that is driving. Either way it's bad news if you're planning on using it like an automatic transmission in a car.

Also, beveling both meshing gears actually doesn't help a bit. Beveling just one helps a little. Actually rounding or beveling the sides of each tooth helps the most and hurts your tooth face width the least. Of course it requires a good hand with a dremel and a lot of patience.

Shifting wise, we use a brass bushing with a shaft press fit inside of it that's threaded on one end and attaches to a pneumatic. The two gears are welded together and free spinning on the shaft on some needle bearings. I can post a section view if that's incredibly confusing.