Gear Box Overhaul: Main Drive Pinion Wear

Hi,
My gear box looks pretty good; no broken teeth and the shafts and bearings look good.
But the main drive pinion and tumbler assembly have too much slop and wear. One can see how the main drive pinion has been deformed wear it drives the the tumbler gear. I'm thinking to have the main drive pinion ground round to have the 'bumps' removed. And then it will ride better in the tumbler bushing.

Has anyone fixed this before? Any better ideas?
I have to hire this work out, since my lathe is my only machine tool.

You need to replace those parts.

allan

Looking at the parts you have shown, I have to wonder if part of the problem is the shaft that the tumbler gear rides on and the bore in the tumbler handle. My lathe had excessive wear in the tumbler handle bore that allowed the gear to away from riding perpendicular to the pinion shaft. That being said I replaced it with a later 102 single handle box. South bend improved the design by casting an additional "ear" on the tumbler handle. Instead of the shaft turning with the tumbler gear, the gear rides on a bearing. I was able to replace my box, and can look to see if my pinion is in better shape than your. If you can find a later tumbler handle with the updates it would be better. If not, consider checking the wear in the tumbler handle bore. DM me if you are interested in me finding my pinion shaft


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The tumbler handle bores are worn and are oversized. I found a new tumbler gear stud shaft and the bore can be sleeved. I'd like to add a needle bearing, but I afraid there is not enough casting to make the bore big enough without significantly weakening it.
The big bore, which the main pinion goes thru is worn too. I thought if I got the pinion ground even and sleeved the bore I'd have it fixed. But I sure would like to find parts in better shape.
I figure the pinion deforms with use and makes its diameter larger, which in turn eats up the tumbler bore. It was very loose and noisy.

What I thought happened to mine is the load on the gear is unsupported on one end(where the nut is) and the natural deflection from the pressure of the gears meshing together causes the two axis of the pinion shaft and the tumbler gear shaft the push away from each other. That said the oils supply to the tumbler shaft is minimal at best by running down the tumbler handle to a hole in the handle casting. I'm no expert at all, but I believe that is why southbend made the later casting with additional support and ran the gear on a needle bearing in lieu of a shaft rotating in a bored hole. I think you might be ok to bush the tumbler gear shaft if you can't find a later model tumbler handle as described.As I said earlier I will try to look and send you pictures of my pinion shaft. I'm attaching a picture of the later design I snagged off of the web. If my pinion will work you're welcome to it. I will be in touch.


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I'm having a new main pinion shaft and tumbler gear made for me. The work cost 1-1/2x what I paid for the lathe 12-years ago, but considering how much use I got out of the machine it is a worth while investment to me.

Just thinking about the overall design of the tumbler handle and gear, I've got to wonder if a it might be better to bush the tumbler gear, make a shouldered bolt to attach rigidly & squarely to the tumbler handle, and let the tumbler gear spin on the shouldered bolt.
-George

fwiw:

http://www.practicalmachinist.com/v...mbler-gear-before-being-destroyed-use-332239/

Gear Box Overhaul

Hi,
I had a new pinion shaft, tumbler gear and tumbler gear shaft made.
The tumbler gear shaft was made from bronze and slightly over-size to accommodate for the wear in the tumbler handle.
Everything went together fine and here are a couple photos: