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Bison chuck internal thread not fully cut?

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  • lakeside53
    replied
    Yes. It's not much different to using soft-jaws, but you are just adjusting your hard portion. Additional to bell mouth - this won't fix scroll problems, but it will help a jaw with worn scroll engagement threads that is now out of radial alignment wrt the other jaws.

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  • J Tiers
    replied
    If a chuck is bell mouthed, which IS usually due to wear, it is easuly corrected by grinding the jaws in the lathe while they are held in their "clamped-on-work" position.

    Many will solemly caution you about all the things that could still be wrong, but I have found the grinding to be, as expected, very effective in correcting the bell-mouthing. If is not intended to correct off-center, but i can have the effect of improving that somewhat. Just don't consider it a cure-all, it is for fixing bell-mouth.

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  • Graydon
    replied
    Originally posted by oldtiffie View Post
    Mount "soft jaws" on the three teeth of a 3-jaw chuck and use a sensible method of boring the soft jaws out - they should be within "tenths" of +Total Indicated Run-out" (TIR) and the problem "outage referred to is very accurately "cancelled out".

    Some 3-jaw chucks require that each jaw be inserted into its own slot in the chuck body during manufacture - keep your jaws in the correct slots.
    Yes, I placed the jaws in their correct locations and matched up the two piece jaws correctly. They have numbers stamped in them and I marked them with a sharpie.

    -Graydon

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  • Peter.
    replied
    Originally posted by danlb View Post
    For a new quality chuck .004 is a lot for a 3 jaw. Is it wobble or is it off center? Wobble is .004 at the jaws and .010 when measured 3 inches out. Off center is .004 at the chuck and close to .004 at 3 inches out.

    Wobble may mean that the end of the "registration collar" is not perpendicular to the axis of the chuck. It could also be due to damaged jaws (bellmouth) and several other causes.

    Off center can mean the jaws are not closing uniformly (could be wear or could be swarf in the scroll gear or even swarf in the gripping part of the jaws) or that the registration bore is not centered on the axis, thus pulling the whole chuck off center.


    Dan
    Bell-mouthing need not be a problem with the jaws (and I would suggest is not the case the majority of the time). I bought a lathe which had a 5" Pratt Burnerd chuck on it. Runout was between 8 and 15 thou each time the jaws were tightened and in fact I found that you could put a piece of stock in the chuck and physically wobble it about hitting the jaws individually - it was badly bell-mouthed but the jaws were in visually good condition.

    I also had a 5.5" PB chuck which has jaws that can swap with the 5" though it was missing the outside set. I tried the outside set from the wobbly chuck and they were a snug fit, so then I tried the inside set off the wobbly chuck and they too were a snug fit. Put some stock in the chuck and it held 0.0015" consistently.

    The jaws were fine, the chuck face was the part that was bent.

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  • oldtiffie
    replied
    Originally posted by Graydon View Post
    Good catch. This was a used Bison chuck off eBay. It is certainly used but I don't think abused terribly. The joints between the two piece jaws were sharp and tight. There were only a few dents and dings. Overall it looks very good. The date was shown on the spec sheet but I forget what it said. It was less than 30 years ago though.

    The factory specs are indeed a good start as a suggestion as to what it might have been when new. I don't expect it to be perfect but I think I can do better than .004"

    Now that it's mounted I'll do some cleaning and tweaking and see what I can get out of it. I really appreciate all the fine suggestions posted by all of you fine gentlemen. Thank you again.
    Mount "soft jaws" on the three teeth of a 3-jaw chuck and use a sensible method of boring the soft jaws out - they should be within "tenths" of +Total Indicated Run-out" (TIR) and the problem "outage referred to is very accurately "cancelled out".

    Some 3-jaw chucks require that each jaw be inserted into its own slot in the chuck body during manufacture - keep your jaws in the correct slots.

    Leave a comment:


  • Graydon
    replied
    Originally posted by CalM View Post
    The OP mentions "picking up" the chuck without qualification to new or used. Using the factory specs are a great bench mark, but do not account for history , experience or "the piece you have".

    two near and two far is fine with me. a piece of printer paper will cut that in half!
    Good catch. This was a used Bison chuck off eBay. It is certainly used but I don't think abused terribly. The joints between the two piece jaws were sharp and tight. There were only a few dents and dings. Overall it looks very good. The date was shown on the spec sheet but I forget what it said. It was less than 30 years ago though.

    The factory specs are indeed a good start as a suggestion as to what it might have been when new. I don't expect it to be perfect but I think I can do better than .004"

    Now that it's mounted I'll do some cleaning and tweaking and see what I can get out of it. I really appreciate all the fine suggestions posted by all of you fine gentlemen. Thank you again.

    Leave a comment:


  • danlb
    replied
    I suggested it because there is a good chance that something is not quite right.

    I have two lathes ( 7x12 and 9x20 ) both made by Sieg ( asian ) that people on this board say are terrible quality. Both currently have 3 jaw scroll chucks installed. One has a touch more than .001 TIR and the other just under .002 TIR. Measured at 2 inches out with 5/8 inch ground rod. They are not up to Bison standards, but they ARE much better than Graydon is seeing with his chuck.

    .004 TIR does not strike me as a "good one" by any measure.

    Dan

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  • CalM
    replied
    Originally posted by danlb View Post
    Cleaning and checking is a good idea.

    According to page 145 of theBISON technical document, ( page 145, titled centering accuracy) you should expect .0016 or better "centering accuracy" at 3 inches from the jaws. Not sure if centering accuracy is TIR or offset from center.

    Dan
    The OP mentions "picking up" the chuck without qualification to new or used. Using the factory specs are a great bench mark, but do not account for history , experience or "the piece you have".

    two near and two far is fine with me. a piece of printer paper will cut that in half!

    Leave a comment:


  • danlb
    replied
    Cleaning and checking is a good idea.

    According to page 145 of theBISON technical document, ( page 145, titled centering accuracy) you should expect .0016 or better "centering accuracy" at 3 inches from the jaws. Not sure if centering accuracy is TIR or offset from center.

    Dan

    Leave a comment:


  • J Tiers
    replied
    Originally posted by Graydon View Post
    The needle moved a total of 0.004".

    .....
    You have a good one then. Don't worry about it, every 3 jaw has errors, and often it is worse than that.

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  • Graydon
    replied
    Originally posted by J Tiers View Post
    Yes... indicate the body. Most all self-respecting chuck manufacturers will make the body concentric. So if the body is "out" then the gripped piece will be.

    A 3 jaw that does better than 3 thou out is a good one for sure. the 4 thou.... is it plus 4 and minus 4? Or does the needle move 4 thou? If the needle moves 4 thou, the actual "off-center" is 2 thou, which I would call perfectly fine.
    The needle moved a total of 0.004".

    I will still go through the chuck and clean the jaws and the scroll. I'll double check the spindle threads and put it all back together. Then I'll indicate the body and I'll let you know what I find.

    The vertical surface of the registration flange on the spindle is less than a couple tenths off. Every place I tried indicating on the spindle was less than .0002". A good workpiece in my 5C collet was also within .0003" in this spindle.

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  • Toolguy
    replied
    I would start by taking out all the jaws and clean out the jaws and scroll. Reassemble and recheck.

    Edit - Old Mart and I were both typing at the same time.

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  • old mart
    replied
    To eliminate possible errors caused by foreign matter contamination, the chuck should be dismantled and thoroughly cleaned. Inspection of the 2 1/4 X 8 thread in the chuck will be easier if you have a dental mirror.

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  • J Tiers
    replied
    Yes... indicate the body. Most all self-respecting chuck manufacturers will make the body concentric. So if the body is "out" then the gripped piece will be.

    A 3 jaw that does better than 3 thou out is a good one for sure. the 4 thou.... is it plus 4 and minus 4? Or does the needle move 4 thou? If the needle moves 4 thou, the actual "off-center" is 2 thou, which I would call perfectly fine.

    Leave a comment:


  • lakeside53
    replied
    0.004 thou "wobble" when you have work chucked can come from the scroll/jaws. do the mean "TIR" or wobble at the face of the chuck? Not that it's really relevant except for balance, but indicate the chuck body just for grins.

    I'd expect better than 4 thou for a decent 3 jaw, but not much less. Sure, sometimes you do find one that is better. They make adjust-tru chucks if it matters to you.

    Leave a comment:

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