Sudden shift in a 3Jaw chuck?

adammil1 · Dec 22, 2021

I have a pretty new 3Jaw chuck it used to run true within 0.001" or so. I was doing some work with heavy chatter and next thing I know the chuck has about 0.025" runout on it.

I indicated the OD of the chuck and that's true within 0.004" which from memory was about right to how I set it up when I mounted it to the backplate so I don't think the shift was at the backplate I don't believe there is more then a few 0.001" slop back their either. I checked the jaws to see if there was crap in between where the reversible jaws mount to the base and that was good. I took all 3 jaws out one by one and reloaded them by jaw order but nothing worked. Right now I'm thinking the issue may be something inside the chuck. Anyone ever seen such a problem before? Any thoughts?

It was a nice chuck a few days ago. How does it shift so fast?

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dana gear · Dec 22, 2021

Process of elimination, assuming you have checked your lathe spindle to confirm it is running true, Use a indicator and bar(side load the spindle) and confirm there is no movement. I have seen chucks run true until they were under load, so you want to confirm there's no problems there. then depending on what type of chuck mount you have, that the mounting is clean and mounted correctly and tight, then it's chuck time.
One of my buddy's purchased a China special chuck and after about a week the scroll inside the chuck had so bad it ended up being unusable.

edwin dirnbeck · Dec 22, 2021

Three jaw chucks are DEAD SIMPLE. tHE SCROLLL PLATE IS THE ONLY MOVING PART THAT AFFECTS ACURACY The thing that you see when you take the jaws out is the scroll plate. That is the only thing that matters.Any new three jaw chuck can be taken apart in 5 minutes.TAKE IS APART AND REPORT BACK. Edwin Dirnbeck

CalG · Dec 22, 2021

something came loose in the mounting, or a dent in the scroll.

DDoug · Dec 23, 2021

edwin dirnbeck said:
Three jaw chucks are DEAD SIMPLE. tHE SCROLLL PLATE IS THE ONLY MOVING PART THAT AFFECTS ACURACY The thing that you see when you take the jaws out is the scroll plate. That is the only thing that matters.Any new three jaw chuck can be taken apart in 5 minutes.TAKE IS APART AND REPORT BACK. Edwin Dirnbeck

Again with the yelling..... :nutter:

edwin dirnbeck · Dec 23, 2021

digger doug said:
Again with the yelling.....

Yes, some times it does make me nuts.This is not a beginners forum.I should have said.Just take the chuck apart,and the problem will be obvious .Edwin Dirnbeck

eKretz · Dec 23, 2021

That is pretty massive runout. Now I'm curious. I can't imagine what would cause that without some serious destruction or something having come loose at the chuck mounting.

adammil1 · Dec 23, 2021

So I took the chuck off the back plate. Back plate is running true to 0.002, and it's a light slip fit to the back of the chuck. So chuck can only move maybe 0.001" on there. None of this explains the 0.025" that I am seeing. Scroll appears to be in good condition with no obvious signs of damage either. Jaws look good with no real signs of wear. I was in a bit of a rush when I tore it apart earlier so I may have missed something but so far nothing's jumping out. I will look at it more tomorrow to see if I missed something.

This was a very nice chuck a few days ago. I verified jaws even went in, in the right order too. So far I am perplexed. Only other thing I haven't tried yet is to put it all back together and see if the problem is local to a given diameter or rather a range of them.

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plastikdreams · Dec 23, 2021

eKretz said:
That is pretty massive runout. Now I'm curious. I can't imagine what would cause that without some serious destruction or something having come loose at the chuck mounting.

I've had some pretty good vibration while parting, but I've never seen it move a chuck. Things don't just shift 25k.

JST · Dec 23, 2021

How's the fit of the scroll on it's "spigot"? Should be a close running fit, but if for any reason it is not, any slip there can cause everything to shift.

I'd not really expect 0.025", although that runout (tir) is only 12.5 thou actual movement off center. But then, I;'d not expect that in any OTHER portion of the chuck either.

If it is fairly new, then you may need to look for any junk that may have been in there from day 1, and which might have been between things, only to come out, fall out during disassembly, and leave a mystery behind.

michiganbuck · Dec 23, 2021

So..the rest of the story..

I put it back together and

Did still have the error
Did Not have the error.

Oh yes, you mentioned that:[ I haven't tried yet is to put it all back together and see if...}

Colt45 · Dec 23, 2021

Might look for cracks in the jaws, jaw carriers, carrier teeth and chuck body, especially the jaw slots.

edwin dirnbeck · Dec 23, 2021

Your first picture seems to show another plate with alan screws . Why didnt you take the alan screws out and see whats behind this door ? Edwin Dirnbeck

michiganbuck · Dec 24, 2021

The scroll plate should likely be flat, so to check this before re-assembly would be good.

plastikdreams · Dec 24, 2021

thermite said:
They surely will if the scroll plate had a flaw, cracked and is trying to hire itself out as a spring-cee clip on steroids.

Well yeah that's a possibility. Lol

tnmgcarbide · Dec 24, 2021

3 jaw's got nothing to do with it . it could'a been a 2-5-6-8
jaw chuck. would not make a difference . he's either got a
china/indian crap chuck, or he just doesn't have the moxie to
know what he's looking to fix . his first fuckup was to ask
here...a bunch of know it all ..impatient assholes, myself included. who'd rather chime about something else than " my
3 jaw cuck won't center"

Scottl · Dec 24, 2021

I would say, perform the reassembly step by step. At each stage indicate the parts to run as true as possible. If things shifted under load every bit of runout can add up. Check for dirt, burrs, or other issues. Also check the fit of the jaws in the slots. In some chucks sudden heavy loads such as severe chatter or a minor crash can actually spring the front of the chuck, making the fit on the jaws looser and that can be a major contributor.

HappyWyo · Dec 24, 2021

You have evidently tried everything from spindle to jaws. After having checked everything in the Chuck, don't be afraid to true up the jaws to run perfect. I like mine to run within .001. Put a piece of stock in the jaws tight, and check run out on the stock. Remember that is how a Chuck is finished. Mark the jaws that need adjusted and polish, sand, grind or what ever you need to do to make the stock run perfect. Remember the jaws are marked 123 for that reason, they were machined in that spot to run true. Even in a four jaws a jaw can get a scratch, gouge, dent or other imperfection that needs polished off or the stock won't run perfectly parallel. You have to keep up on your maintenance if you want perfection. I noticed a lot of chips on your lathe. Cleanliness is a must in being a perfectionist. I have a granddaughter who runs around with a broom, rag, magnet, and paintbrush cleaning chips and painting scratches, so I have an advantage, and it helps.

Peter. · Dec 24, 2021

I broke an insert and had a piece of stainless stock slip in the chuck one time and it spin-welded a piece of stock onto the gripping face of one of the jaws. Couldn't even see it at first but it was there and getting rid of it put the chuck to rights.

HappyWyo · Dec 24, 2021

I have hardness tested every Chuck in the shop and they are all the same hardness regardless of where they are made. None of them are very hard and they all are capable of damage

Sudden shift in a 3Jaw chuck?

Titanium

Hot Rolled

Hot Rolled

Diamond

Diamond

Hot Rolled

Diamond; Mod Squad

Titanium

Diamond

Diamond

Diamond

Hot Rolled

Hot Rolled

Diamond

Diamond

Diamond

Diamond

Aluminum

Titanium

Aluminum

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