new chuck

Hi all
I'd like to draw upon the collective wisdom of the you all. I've just bought a direct mouning (no back plate) 6" 4 jaw independent chuck for
my Super 7 and am far from happy with it. With a decent quality test bar dialed in at the jaws, there is a good 1/8" run out at 12" from the chuck. The chuck body does not sit parallel to the spindle axis - the rim wobbles by about 15thou. Not much good really so obviously its going back to the well known supplier. I won't identify them until they've had plenty of oportunity to rectify the situation.
Given that I can't afford genuine Myford prices, what is everyone's experience of recent purchases and suppliers? Perhaps a backplate mounted chuck would be a better idea. At least then I can make sure its machined carefully to get the chuck parallel and concentric to the spindle. Any recommendations for a make and supplier?
cheers
Toby
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While the chuck body should run a lot truer than it currently does,do not expect to true something up at the jaws and have it running true 12" out.That`s not how four jaws work.
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Toby Firstly, I assume the problem is lack of parrellism, ie the bar is running truer at the jaws but the error increases as you go down the bed. In this case I would check the register on the spindle.
Secondly, if the register is OK (you can check with a faceplate,) the problem is with the chuck, make sure it is screwing home properly and is snug against the register.
I am rather surprised at this as modern chucks are pretty good and in my experience are better made than this. Peter
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On Mon, 9 Feb 2009 01:30:58 -0800 (PST), snipped-for-privacy@hotmail.com wrote:

To echo Peter Comans comments, take the chuck off and make sure you haven't got a little piece of swarf trapped between the spindle & chuck registers. I turned up a *perfect* backplate last week, then got awful runout after I took it off and mounted the collet chuck on it. Spent ages trying to dial it in before I took it off again and noticed a bit of swarf stuck as above.
Peter
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Peter, Peter and others
thanks for you thoughts. I'm fairly sure its not a problem of swarf etc causing the wobble. My 3 jaw and face plate clock in with only 1 and 2 thou wobble repeatedly and the new 4 jaw was cleaned and fitted several times with identical results of 14 thou.
I've not checked the spindle nose given that the 3 jaw and plate are pretty good.
We'll see what the replacement chuck is like before naming the supplier, although their service has been friendly and courteous so far,
cheers
Toby

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Hi again
just an update.on the new body mounted chuck with 14 thou runout......
the replacement chuck has now arrived and is better. The body runout is now only 7 thou at the outer diameter. Is this still too much? I'm not sure. I'm wondering about very carefully trying a bit of scraping (of the chuck not the spindle of course) to improve the fit.
I'd be interested in people's opinions on this - do I just return it again or have a go at it with the scraper? Will the body be able to rotate enough or will the parallel section of the spindle nose prevent the rotation?
cheers
Toby
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On or around Wed, 25 Feb 2009 04:54:00 -0800 (PST), Toby

2 points:
1) how much runout do you have on a workpiece held in the chuck?
2) does it cause excess vibration at full speed.
If it holds true and doesn't vibe, then it's probably OK. Any imbalance will however put extra strain on the spindle and bearings.
I'd be inclined to thing that 7 thou still sounds too much, but bear in mind what you're doing with it. Was this a 4-jaw independent?
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wrote:

Based on the fact that you said on 11/2/09 that....
"After a brief and friendly chat the retailer was very willing to say that 14 thou runout is far too much on the body of a chuck. The claim is that most items being dispatched are clocked on a test spindle but in all the snow and bother of last week mine was forgotten."
We must assume therefore that 7 thou is acceptable to the vendor.<G>
Personally I would NOT do any scraping of the register of the chuck. If this is currently a "nice" fit on the the nose then that is the way it should stay. Assuming you machined something then took the chuck off, say for a mill op on the part, then put it back on, you would want the component to still be true. Scrape the register and you have lost that!.
I would expect that 7 thou TIR would not affect balance overly at your max speed. However if you are concerned then remove all jaws, or clamp and clock a piece of "round bar" and spin it up to your max speed and see!
Richard
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enlightened us thusly:

bought a TOS (I think - or equivalent) from J&L for the stuident, with a part-finished backlplate for the Student's L-zero nose. Mount the backplate and machine it **very** carefully to fit, fut chuck and job's been a good'un so far.
8" chuck, total price came in at about 350 I think.
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I took delivery of a supply of Indian made 4 jaw chucks originally bought by a well know Northern England supplier of Indian goods.
These had been machined with the body slightly tilted when the jaw slots were milled in with the result that they rotated drunkenly and were basically scrap.
I did recover one by gripping the chuck jaws onto a freshly turned bar in a 3 jaw and refacing the back and register.
Even though afterwards it turned true the body revolved out of kilter, to machine the chuck all over would have been too expensive given time and the base cost of the chuck.
Most were fastened onto a piece of hefty angle iron so they could be held in a vise as a 4 jaw vise for holding odd shaped castings etc and given away
John S.
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You might saave a few people some postage and bother if you did name them.
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Hi all again,
just an update. After a brief and friendly chat the retailer was very willing to say that 14 thou runout is far too much on the body of a chuck. The claim is that most items being dispatched are clocked on a test spindle but in all the snow and bother of last week mine was forgotten. I'm happy to accept this as a checked replacement is promised by return of post.
I'll see what the replacement is like and let you all know of the outcome, but its looking like good service so far.
cheers
Toby

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Toby Wrote:

Hi Tony, Firstr are you sure the chuck is screwing on all the way, check with a black marking pen that it is not binding before both the axial and the radial faces contact. Second, if you ae worried about being out at twelve inches, why not use a toolpost grinder to "bore" the jaws parallel, but do remember to do this under tension. Ned Ludd
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