Woodturning Lathe Build Process
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Posted 6th April 2024
I was using the lathe again this morning to make another tool handle and I noticed that there was a lot of vibration. After a quick investigation, it became clear that the motor pulley was wobbling on the motor shaft and that was making the motor vibrate. I'm sure I could deal with it by clamping the motor assembly down better (it was only held to the bench with one clamp), but I'm not happy about the level of vibration.
I mentioned in an earlier post that the motor pulley had been a pain to fit as the shaft of the motor turned out to be wider at the end than at the base. I think what's causing the vibration is that the pulley doesn't have a perfectly fitting hole in the middle (as it needed to be enlarged to get it over the end) and hence it's moving back and forth a bit as the shaft rotates. The only decent way I can think of dealing with this is to sort out the motor shaft (and then make a new pulley).
The first step was to dismantle the motor to have a better look at what's going on:
I mounted the shaft between centres on the lathe to see whether that would allow it to run fairly true (and hence give me a relatively easy way of making the shaft a consistent diameter and concentric with the motor axis).
Running the lathe at a low speed (and with no drive dog, so just relying on friction to spin it), it was obvious that the shaft wasn't running true relative to the two centres. This is a close-up of the questionable end:
It's not that obvious in the photo, but the tip balloons out a bit. The bearing sits on a register that looks to be 19.05 mm (3/4"), so there's no way I'd be able to get the bearing (and hence the retention plate and the fan) off without first doing something about the end of the shaft (the shaft end is 19.35 mm at the tip). To make things even more difficult, the shaft has been hardened, so turning it won't be trivial.
Looking at the end of the shaft, it's clear that it has had some abuse at some point in its life: the centre hole looks pretty awful (which won't have helped it run true when mounted between centres):
Compare that with the centre hole on the other end of the shaft, which looks a lot better:
I'm not sure what to do about this to be honest. I've thought of a few approaches, but none seem great.
Approach 1:
- Re-assemble the motor
- Run it and, while running, use an angle grinder to get the end of the shaft down to less than 19.05 mm.
- If there's enough 19.05 mm shaft left to be usable and it runs concentrically with the bearing, stop there.
Approach 2:
As approach 1, but assuming the shaft isn't looking sufficiently usable after the angle grinder attention.
- Pull the bearing, bearing backing plate and fan off and then re-fit the bearing.
- Mount the shaft on the lathe, using a fixed-steady to support the outside of the bearing.
- Try skimming the shaft with some carbide tools to get a smooth shank at some diameter or other (< 19.05 mm)
- If I'm not feeling confident in the concentricity of the result, reduce the diameter even further (< 15 mm probably) and shrink fit a (non-hardened) sleeve over the top, then reassemble the motor and mount the entire motor to the bed of the lathe and run the motor while turning a new concentric shank from the non-hardened sleeve.
Approach 3:
- Just cut the end with an angle grinder, hopefully leaving enough of a concentric section to be usable (similar to approach 1, really).
I'm probably leaning towards approach 1 (with a lot of hoping that I can do it without having to resort to approach 2), but I'd welcome any other suggestions.
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