# Broach Bushing



## francist (Aug 4, 2019)

Continuing along with my gear making expedition, I decided to try some broaching. Never done it before, and although the connection to gear making may not be readily apparent there actually is one.

I have two Atlas lathes, and in order to make up the compound change gear configurations they use a bushing sleeve that has what amounts to two opposing keys that mate with two opposing keyways in the change gears. When you stack two gears on the one sleeve, the integral splines lock the two individual gears into one compound gear. It's a reasonable arrangement and seems to work well, but it does mean that any gears need to have the two opposing keyways cut in to their bore and that looked like it would be the tricky part.

I could buy the broach no problem -- KBC had a 1/8" Style "A" broach that would work fine but I would need to come up with a bushing. So I devised a scheme to have the bushing itself set the clocking for the keyways, that way I should only have to really fuss with critical alignment the first time around.

Making the bushing went pretty smoothly. I used a 1/8" width slotting cutter on the horizontal miller and held the bushing in a couple of custom-made vise jaw liners. Once the one slot was cut for the broach, I could keep the setup but rotate the blank exactly 180-degrees and cut a second slot at keyway depth on the opposite side. 








Well that was the plan and that's what I did, but somewhere in the process I lost some  of the "exactly" part. My two slots ended up being a bit offset from each other. Not by much, maybe a few thousandths, but enough that I could see it and I figured for sure I'd scrapped the part.








But then I figured, what the heck? Try it and see what happens, it's just a part. And by gum it worked.

The idea with the two slots in the bushing is that the first deep slot guides the broach for the first keyway on one side of the gear bore, and then by using a small length of key stock the bushing can be clocked 180 degrees to cut the second keyway on the exact opposite side of the bore. In practise there was just enough play in my guide slots that I could use a slip of paper as a shim on one side to correct for my alignment error. Much to my surprise, when I tried the splined change gear sleeve it slid right in. 





I may end up making another bushing in the hopes of not repeating the error, or maybe I'll just leave it for a while and see what happens. I want to try making a second set of change gears out of Acetron (yes I know I can buy original gears on Ebay) for my fire salvaged Craftsman so we'll see where that goes.




As always, thanks for looking.

-frank


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## Ulma Doctor (Aug 4, 2019)

nice work Frank!


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## francist (Aug 4, 2019)

Thanks Mike, I appreciate that!

-f


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## brino (Aug 5, 2019)

I can't see any misalignment from here!
Nicely done.

-brino


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## francist (Aug 5, 2019)

Ahh, you're too kind my friend   Thanks Brino.

-frank


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