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Clattering Backgears

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Steve35518/10/2021 23:11:53
128 forum posts
87 photos

Hi

My backgears don’t half make a lot of noise. I’ve tightened and oiled everything I can think of. I’m also getting a light “parallel striped longitudinal “ chatter pattern which may align with the teeth on the large main spindle gear that the small back gear is meshing with.

Any thoughts?

Cheers

Steve

Steviegtr19/10/2021 00:56:31
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2269 forum posts
313 photos

Make & model of Lathe. May help with answers.

Steve.

peak419/10/2021 01:36:48
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1537 forum posts
165 photos

It could be that you have the mesh a bit tight, or maybe the bores/bushes are worn.
I lube my Myford gears with aerosol motorcycle chain lube.
It dries fairly sticky, says where it's put, and cushions the teeth quite well; I'd only use it in gears under a cover though to save the swarf sticking to them.

Bill.

Ady119/10/2021 07:22:27
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4810 forum posts
717 photos

Probbly the bores

not done it yet19/10/2021 08:05:42
6430 forum posts
20 photos
Posted by peak4 on 19/10/2021 01:36:48:

It could be that you have the mesh a bit tight, or maybe the bores/bushes are worn.
I lube my Myford gears with aerosol motorcycle chain lube.
It dries fairly sticky, says where it's put, and cushions the teeth quite well; I'd only use it in gears under a cover though to save the swarf sticking to them.

Bill.

Poster says “back-gears” not feed gearing. Seems like something is badly worn. There again, poster may be using wrong terminology?

Martin Connelly19/10/2021 08:51:49
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1930 forum posts
207 photos

Parallel striped longitudinal pattern makes me suspect either rack and pinion drive or leadscrew drive of the carriage causing the patterning. It would be interesting to know if the patterning is at the same pitch as the carriage drive mechanism. There is a possibility that it has been lifted incorrectly and a sling has distorted a feed shaft or leadscrew. A DTI mounted on the carriage and contacting the slideways of the bed would show if the carriage is doing a bit of a drunken walk as it travels along the bed.

Martin C

Michael Gilligan19/10/2021 09:35:01
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19258 forum posts
959 photos
Posted by Steviegtr on 19/10/2021 00:56:31:

Make & model of Lathe. May help with answers.

Steve.

.

It’s just a wild guess [I accept that he may have another lathe] … but Steve has recently been discussing his Zyto.

MichaelG.

.

Ref. __ https://www.model-engineer.co.uk/forums/postings.asp?th=174865

Edited By Michael Gilligan on 19/10/2021 09:42:13

Steviegtr19/10/2021 15:01:51
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2269 forum posts
313 photos

Ah yes Michael, that's probably why he has not responded.

Steve.

Steve35519/10/2021 23:31:11
128 forum posts
87 photos

Sorry, I actually had to work today! Yes indeed it’s a Zyto.

in fact there are two rattles I think. One related to the back gears. The back gear spindle isn’t in great shape (the rest of the lathe has little wear it seems. But I managed to improve the way the back gears turn - the large gear was a bit sticky, so they all turn smoothly now. I can’t see a way to adjust the way the gears mesh.

The other rattle occurs when the back gears are disengaged. It goes away when I take a fairly deep cut (eg. 10 thou), then returns when I wind the tool bit off the workpiece. It seems to come from the chuck, but this is unlikely as everything seems tight.

Steve35519/10/2021 23:32:23
128 forum posts
87 photos
Posted by Martin Connelly on 19/10/2021 08:51:49:

Parallel striped longitudinal pattern makes me suspect either rack and pinion drive or leadscrew drive of the carriage causing the patterning. It would be interesting to know if the patterning is at the same pitch as the carriage drive mechanism. There is a possibility that it has been lifted incorrectly and a sling has distorted a feed shaft or leadscrew. A DTI mounted on the carriage and contacting the slideways of the bed would show if the carriage is doing a bit of a drunken walk as it travels along the bed.

Martin C

Thanks Martin, I will give that a try in the morning.

Steve

Tim Stevens20/10/2021 11:02:38
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1490 forum posts

If the back gear assembly is not in perfect balance, and is going round in gear but not actually driving, there will be a tendency for clatter as the clearance between the gears is changing sides (as the out-of-balance is pulled down on alternating sides by gravity). To test this, put a small load on the back gear spindle - perhaps by pressing a piece of wood against the plain shaft - and see if this reduces a) the rattle and b) the striping. To balance the shaft properly involves setting it (away from the lathe) so it can rotate completely freely - on a close-fitting shaft between new rolling bearings, perhaps. Then, allow the heavy side to fall to the bottom, and mark it. Then remove metal on the heavy side - or add to the light side, until it stops in any position with no tendency to settle in one place. It takes time, sorry. Or, find a way of moving it out of mesh when you are not needing it.

Cheers, Tim

Edited By Tim Stevens on 20/10/2021 11:07:58

Edited By Tim Stevens on 20/10/2021 11:08:10

Steve35520/10/2021 12:12:00
128 forum posts
87 photos
Posted by Tim Stevens on 20/10/2021 11:02:38:

If the back gear assembly is not in perfect balance, and is going round in gear but not actually driving, there will be a tendency for clatter as the clearance between the gears is changing sides (as the out-of-balance is pulled down on alternating sides by gravity). To test this, put a small load on the back gear spindle - perhaps by pressing a piece of wood against the plain shaft - and see if this reduces a) the rattle and b) the striping. To balance the shaft properly involves setting it (away from the lathe) so it can rotate completely freely - on a close-fitting shaft between new rolling bearings, perhaps. Then, allow the heavy side to fall to the bottom, and mark it. Then remove metal on the heavy side - or add to the light side, until it stops in any position with no tendency to settle in one place. It takes time, sorry. Or, find a way of moving it out of mesh when you are not needing it.

Cheers, Tim

Edited By Tim Stevens on 20/10/2021 11:07:58

Edited By Tim Stevens on 20/10/2021 11:08:10

I think you’re onto something Tim.

I suspected something like that, because I was able to simulate a “single clatter“ by manipulating the play between the back gears and the main gears. I just tried pressing a piece of wood against the back gear spindle, and indeed I noticed a significant reduction in the clatter. I don’t have anything to turn at the moment, so I’m not in a position to say whether it’s reduces or eliminates chatter.

What is clear, is that there is significant play in the right-hand back gear spindle bearing. It is damping this that reduces the clatter. I’ve no idea how to fix that, as the bearing is an integral part of the headstock. It could be that the spindle is worn, I’ll have a good look at it later.

 

This is certainly a journey!


Steve

Edited By Steve355 on 20/10/2021 12:12:58

Edited By Steve355 on 20/10/2021 12:13:27

Howard Lewis22/10/2021 20:11:01
5528 forum posts
13 photos

Idle thoughts.

If the Back Gear is engaged by rotating eccentric bushes around the shaft, can the travel be increased to reduce the backlash between the gears on the Back Gear shaft and the Mandrel?

Ideally, backlash should be such that sheet of paper (about 0.003" / 0.076 mm ) just passes through the mesh.

If the bushes are worn, rather than the shaft, could you make new, and fit, closer fitting bushes?

If it is the changewheeels that are noisy, again, setting the backlash should reduce the noise.

Excess backlash is likely to produce clatter, especially when lightly loaded, and driven by a single phase motor.

Too little or no backlash is likely to produce a groaning noise rather than a clatter.

This assumes that all the chnagewheels are correct for the lathe, i e correct DP and Pressure Angle to mesh with the driving gear on the Mandrel..

The noise is caused by a slight variation in drive speed, and the driving belts may cause this. Cheap / worn belts sometimes are swollen around the join, and this can cause problems.

HTH

Howard

Steve35522/10/2021 21:11:57
128 forum posts
87 photos
Posted by Howard Lewis on 22/10/2021 20:11:01:

Idle thoughts.

If the Back Gear is engaged by rotating eccentric bushes around the shaft, can the travel be increased to reduce the backlash between the gears on the Back Gear shaft and the Mandrel?

Ideally, backlash should be such that sheet of paper (about 0.003" / 0.076 mm ) just passes through the mesh.

If the bushes are worn, rather than the shaft, could you make new, and fit, closer fitting bushes?

If it is the changewheeels that are noisy, again, setting the backlash should reduce the noise.

Excess backlash is likely to produce clatter, especially when lightly loaded, and driven by a single phase motor.

Too little or no backlash is likely to produce a groaning noise rather than a clatter.

This assumes that all the chnagewheels are correct for the lathe, i e correct DP and Pressure Angle to mesh with the driving gear on the Mandrel..

The noise is caused by a slight variation in drive speed, and the driving belts may cause this. Cheap / worn belts sometimes are swollen around the join, and this can cause problems.

HTH

Howard


the back gears are engaged by simply sliding the back gear shaft an inch or so such that the gears engage.
I think it’s the bushes that are worn rather than the shaft, but they aren’t bushes as such, just holes in the cast iron that supports the shaft, so they can’t be replaced.

I have no reason to think that the change wheels aren’t original, but it is possible, the lathe uses standard Myford sized gears.

I tried reducing the backlash by trying to offset the two back gears slightly, but it didn’t seem to work.

There is a grub screw on the back of one of the arms that holds the shaft. I presumed it was to hold the back gears on the on or off position. I might have a go at tightening it a little to see if it makes any difference.

thanks

Steve

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