Lathe chuck

rzw0wr

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How concentric is the inside back plate mounting hole to the out side of the chuck body?

I made a new back plate for my new 4 jaw chuck.

The chuck fits tight enough that I need to tap it on with a rubber mallet.

When I check the chuck on the lathe with the back plate I get about .008" run out.

I double checked the lip on the back plate where the chuck seats an I get .000".

I measured the back plate seating area on the chuck to the outside and it is off in places about .003.
 

Cadillac

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Did you try indexing the chuck on the backplate to see if it changes. Indicate something in the 4jaw mounted on the lathe then check the OD of chuck to see if it matches.
 

darkzero

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I would say it depends on the quality of the chuck. It should be pretty concentric but not perfect. I would say .008" tir is a bit much. But if it's a 4-jaw independent it really wouldn't matter much cause each jaw is independently adjustable. If the runout doesn't cause your lathe to vibrate then it should be fine. It probably would bother me though. :D

An easy way to fix it if so desired is to machine the registration boss on the adapter undersize, that way you can tap the body true. Down side to this is if you do any heavy maching there's a chance the chuck can move since the boss is no longer doing its job.
 

Bob Korves

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What style mount do you have on your lathe? (threaded, A1, D1, or some other)
 

rzw0wr

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Bob,
It is a Bolton lathe.

It is a bastard mount. None of the standard mounts.
The chuck plate has hole in middle to mount to a flange on the output shaft.

It is a 6" chuck from Shars.
 

rzw0wr

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I indicated the chuck on the lathe and marked the readings on the chuck.
Transferred the dims to the back plate.

Removed the back plate a put the .008" at the .000" mark.

Checked the chuck again and the readings match what is on the chuck.
The back plate is ok.
I think the chuck is out of round to the seat.
 

mikey

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Not sure if there is a real issue here. If this was me, I would begin by determining how concentric the spindle is, checking both the spindle taper and the chuck register. This would give me a baseline. Any departure from these numbers would be due to the stuff mounted on the spindle.

Then I would mount the back plate on the spindle and check the run out at the rim of the back plate. If the rim is turned clean then it gives you an idea of how the plate sits on the spindle register.

Then I would mount the chuck and indicate the machined surface inside the chuck. Most chucks have a central hub around which the scroll moves. It is the only part of the chuck that should be concentric with the recess in back of the chuck and I would indicate the run out there. This should tell you how accurate the machining is on the chuck. The outside of a quality chuck usually matches the inside hub but not sure on an import chuck.

In most cases, run out on lathe chucks is a moot point when the chucks are used properly. If you are talking about a 3 jaw then it will be dead on accurate for first operation work. If you are using it for second operations work then no chuck will be all that accurate. If you are talking about a 4 jaw independent chuck then run out is meaningless because you can adjust it out.

If you are talking about a 3 jaw then you might do a first op turning and check to see that the piece is concentric; it should be. If the jaws are aligned correctly then the work piece should also be straight. If all of this is true then I wouldn't worry too much about it.
 

rzw0wr

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Spindle is .000" per indicator.
The chuck wobbles and shakes my lathe anything over 250 rpm.
Everything on the lathe and back plate appear to be zero per an indicator.

No taper.
Just lip or register for the back plate to seat on.
The back plate also has a register for the chuck.

Both read zero run out when spun.
 

mikey

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Okay, the spindle has zero run out, the spindle register has zero run out and the backing plate register where the chuck fits has zero run out. That just leaves the chuck and if it is vibrating badly at anything over 250 rpm then the chuck is out of balance. You indicated that you had to use a hammer to seat the chuck on the back plate so it isn't the fit and it isn't the bolts that lock the chuck to the back plate so it has to be the chuck that is imbalanced. Might be you need to return the chuck.

What I don't understand is this: "When I check the chuck on the lathe with the back plate I get about .008" run out." And this: "I measured the back plate seating area on the chuck to the outside and it is off in places about .003."

Where are you measuring the 0.008" of run out - on the body of the chuck? If I understand you correctly, you are saying that you measured from the inside of the chuck register (the hole in the back of the chuck) to the outside rim of the chuck and get variations of 0.003" on the OD of the chuck. If this is so then maybe the chuck is poorly machined and, again, maybe you need to return the chuck.
 

higgite

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I don’t see where you have told us if it’s an independent 4-jaw or a 4-jaw scroll chuck. Either way, have you run it with the jaws removed to see if it’s still out of balance? If your lathe still wobbles with the jaws out of the chuck, IMHO it doesn’t really matter why, just send it back. This is assuming there is no imbalance when you run the lathe with a bare spindle or with just the backplate mounted without the chuck.

Tom
 

rzw0wr

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Well, I got an email from Shars.
They said about the same thing as you Tom.

I put a bar in the chuck and zeroed it in and walla nor wobble at 500 rpm.

It is a 4 jaw independent chuck. my first to set up and work with.

Also got to thinking.
If I run the chuck off center it will wobble.

Will head stock bearing preload cause this?
Would adding a little preload solve this problem?
How do you know how much preload to put in?

Thanks for the replies.

Dale
 
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Cadillac

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Yes turning off center will create a imbalance. What size lathe we dealing with?
 

rzw0wr

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a 10 x 20.
About 200 lbs.
 

mikey

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So, the wobble you got at 250 rpm was due to the jaws being unloaded and in different positions, I assume. Once you loaded and centered a bar the chuck runs smooth so it looks like the chuck is okay, right? It's okay; first time using a chuck like this so you won't know this stuff.

Yes, if you turn an off-center work piece you will have vibration because of the unbalanced load. To deal with it, turn down your lathe speed until it runs without vibrating and cut as usual. It is the unbalanced load that is causing the vibration and this has nothing to do with spindle bearing preload.
 

Cadillac

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Bolting the lathe down to a tabletop or stand can help with them issues.
 

mmcmdl

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Bolt a counterbalance onto your chuck if higher rpm is needed . Small as well as some of the largest lathes I've run needed to be counterbalanced when running fixtures etc thrown off center . If your lathe isn't bolted down , you may be chasing it across the shop floor one day !
 
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