3 jaw chuck runout issue
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  1. #1
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    Question 3 jaw chuck runout issue

    Hello, I recently got my first lathe. It's a south bend model 9a. It came with a 8"(pretty sure it is) Phase II 3 jaw chuck. The runout on the base of the chuck is not bad. But if I put anything in the chuck it's all over the place.

    3 jaw chuck problem 1 - YouTube
    3 jaw chuck problem 2 - YouTube

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    First thing to check is that both parts of each jaw have numbers (1,2 or 3) that match the number next to the slot in the chuck body.

    Then check if the jaws are gripping the test bar along their entire length. If the jaws only contact the bar at the inner end of the gripping surface, the bar will wobble at random. You did check that the bar is straight, right?

    Next, check the face runout on the chuck body.

    Next, get a 6 inch 4-jaw chuck and get rid of the 8 inch 3-jaw. It is entirely too big for that little 9 inch South Bend.

    Larry
    Last edited by L Vanice; 11-21-2020 at 05:26 PM.

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    and post the numbers, that photo is not very clear.
    Could be a bug or burr between the chuck and mounting plate, check that the mounting plate is/runs flat true, check that the spindle register is running true.

    *Most likely just the chuck's fault if the jaws are in the right number place (as larry said)then the chuck is not in very good condition. Fixing it likely not worth the effort for a new guy.

    *do check the register to run true..if not then come back and tell what.

    Once you get the feel for truing a 4jaw for one-up and the like you will find that is the way to go with a less than perfect lathe.

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    My money (though not a lot cos I'm a tightwad ) is on jaw mismatch.

    Failing that, you have a 4X'd chuck.

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    Quote Originally Posted by vicfi View Post
    Hello, I recently got my first lathe. It's a south bend model 9a. It came with a 8"(pretty sure it is) Phase II 3 jaw chuck. The runout on the base of the chuck is not bad. But if I put anything in the chuck it's all over the place.

    3 jaw chuck problem 2 - YouTube
    That test bar looks a little odd. How do we know that it is both round and straight?

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    7 seconds of video with the dial indicator so washed out by light glare that it is not visible tells me nothing. If you are expecting a 3 jaw chuck to be perfect you are asking too much, they are not, and every time you chuck the same piece there will be a variation. Get a 4 jaw independent chuck.

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    You have gotten good advice above. Keep in mind a couple of things:
    1. A 3-jaw chuck is a convenience tool, and not designed for highest precision. I purchased a new (old stock) 3-jaw chuck about 18 months ago, a very nice Swedish-made 6" unit, and it checked out very well as brand-new regarding runout. I could flip a rod end for end to turn the entire length, and had matched cuts within .0003 of perfect concentricity. As I have used the chuck, that is drifting to higher values, still under /001, but definitely wearing in. In general terms, no new 3-jaw chuck is ever specified to have better than about .003" TIR
    2. The runout present in a chuck has two general components: offset from center, and angular runout. Make sure what you are looking at. My money is on the mis-matched jaw theory (offset from center), but you should check the runout along the length of the protruding bar as well as at one point.

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    My best 3 jaw on my 9” SB lathe has a tir of 2 thou. My worst is a Crown 3J (last time I bothered to measure) at least 30 thou out and bell mouthed. Guess which one I put on the lathe before the next door neighbor's kid comes over...?

    L7

    (The kid isn’t getting let loose on the bigger lathes yet)

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    A good trick when you can do it is to have a little extra stock and finish a part between centers.

    Do all IDs from one end, then skim the OD and part-off the part so it is true even with a crap chuck.

    Have a very good 3 jaw and it mounted on a adjust-true mount.

    Get used to using a good 4 jaw.

    Note a crap 4jaw can still have wobble with the indicated place spot on.

    The chuck makes the lathe. You can find chucks bragging no TIR listed .008. 003 .00015 whatever...the close ones are pricy.. I have used chucks that stayed under .001 for a good long time grinding.

    Here one bragging .0008 tir and .0012 wobble, for about $600..
    https://www.mscdirect.com/product/details/08574055

    One for half that price with no specs / likely dead on to .008 out (?)
    https://www.mscdirect.com/product/details/03795853

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    Thanks for the help! It seems the chuck on there is just junk. Tried setting the jaws right but no luck. Looking into getting a bison chuck but having trouble finding a finished back plate. Also turns out the chuck on there is a 6" not an 8". I found a used bison 6 1/4" 3 jaw with a back plate for $600.

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    Used Bison 6 1/4" for $600 is way high, considering what you are going to put it on. One of those things that makes no business sense, even though you are not a business.

    1) You can get 3 jaw chucks (if you MUST have one) new for quite a bit less, and they will probably serve you well. Check the importers. (I would not do that yet)

    2) You can look that one over and see if there is an issue with it. I'd do that first, since it may save you a bunch of money, and at worst you will learn something..

    I see two things in your videos.

    A) I see the OD is slightly "out", as in 3 or so thou total. You made a great move checking that! Most do not think of it.
    Almost any chuck from a halfway credible maker will be well under a thou total when checked. So, with that amount on the OD, it is dollars to dog poop that the mounting plate is "out" a bit (not made well), OR that there is something holding the chuck cocked vs the spindle centerline, etc. The chuck itself will be better than what we see there.

    B) I see a whole lot of runout on stock gripped in the chuck. Too much for regular 3 jaw nonsense, and too little for jaws in the wrong places/wrong order. Crud in between stuff can do that, and so can a backplate that is "out" a bit, not made well.

    What I would do is to unscrew the chuck, and look at all the threads and mating surfaces, looking for dings, dirt, chips, etc that can hold the chuck out of square. Check the back surface of the plate where it bottoms on the spindle, and the threads inside the adapter plate as well as the spindle threads.

    If no joy, I would take the chuck off the backplate (there should usually be 3 or 4 screws going through from the front), and check that for crap in between. Also check to see whether the chuck is snugly mounted, or if it can slide around a small amount. It should be pretty darn snug.

    If no joy, I would then re-mount the plate, without the chuck. Check the face of the plate at the outside, where the chuck mates to the plate. First, I would check to see if that surface is wobbling, using indicator with the plunger of the indicator pointing along the bed parallel to the spindle. It should be dead steady.

    Next I would (if it is possible with the tip of that indicator) check the "spigot" of the back plate, the OD that fits inside the back of the chuck to align it, with the indicator radial as you did with the chuck. It should be dead steady.

    If any of those things are not correct, the chuck won't be mounted right relative to the spindle. The good news is that fixing those is an easy turning job, and of course crap stuck in between, that you just clean out.

    If none of those things seems to be the issue, there are "more interesting things to check as well.

    Final question: Are the jaws snug and held steady even when not tightened on anything? Or do they wiggle around and rock back and forth a bit?

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    We are Indian Manufacturers of Lathe Chucks and Other Workholding devices and need help exporting our products to Australia and New Zealand. Anyone who can help us out??

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    JST’s very well written response should be in a sticky for future readers.

    L7

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    Quote Originally Posted by lucky7 View Post
    JST’s very well written response should be in a sticky for future readers.

    L7
    Yes, however....I don't see anything about "get a 4 jaw chuck" in there....

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    If your mounting plate runs true at the face and there is .010 of clearance at the holding screws, you might soft hammer knock and then tighten the chuck that amount and may be able to achieve a close center on a part. If the jaws are in the wrong place or in poor condition getting a knock in zero may still have part wobble. knock in may be needed for each part if the chuck is worn out. A scroll chuck can be taken apart and a shim set around the scroll to make it run better, perhaps from .010 to .003 sometimes..

    *Most often the chuck OD and face should run better than .002 or so. if the chuck body is way off then nothing good can be expected at the jaws.

    The jaws may be in the wrong place or the chuck holding screws may be in the wrong place /the mounting plate may be designed poorly and so not make zero face if mounted wrong/ the lathe register may be wore at the diameter or face/ the spindle tube may be out of whack from a wreck/ the spindle may have too much clearance at the bearings/

    New chucks are often advertised to be good for .008 to .0002 and many don't even list the run-out. So a new low-class chuck may have run out of .010 including wobble, or you may be chance lucky and get one with .003 or less.

    Perhaps someone here can mention/name a low price chuck that will run to .003.

    Buying an ebay used chuck or an ebay new chuck you may be lucky and get a .003 or better chuck or get a .010 off chuck.

    A decent 4jaw can be center adjusted to get near zero and is often the best choice for someone not willing to pay the big bucks needed to buy the better chuck.

    The best 3 jaw is likely to run out .003 or so after a few years of use/abuse.

    Regrinding a chuck is not good for a lathe and often does not restore a badly worn-out chuck to better than .003.

    A seasoned lathe hand often makes do with a .003 and more error chuck with knocking/ turning the part/adding a shim/ tightening the other jaw first/ hang way out and center support/ run in a stady/ having an adjust true mount/ finishing between centers and such to make print spec..not dead zero on every part.

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    I see you have bolt on jaws
    Check if the keys fit properly
    BTW A lathe uses up a couple of chucks in its life
    Like tires on a car
    Peter

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    Quote Originally Posted by Peter from Holland View Post
    I see you have bolt on jaws
    Check if the keys fit properly
    BTW A lathe uses up a couple of chucks in its life
    Like tires on a car
    Peter
    And that they are in the right place with numbering them first and then moving about.

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    Are you sure the top jaws are a match for the bottom halves for that particular chuck. They appear to be American Standard style jaws. I have several chucks with the same style jaws, however in every case the top jaws directly match the bottom halves. In your case they overlap both length ways and side to side. This makes me think they are not the right top halves for your application.

    If you want to keep the chuck you can always remove the current top halves and replace them with soft jaws. A company called Monster Jaws makes a variety of hard and soft jaw replacements. They might have what you need. Replacements for 8" jaws usually run between $45.00 and $60.00 depending on material and height.

    MonsterJaws Mfg - High Quality Chuck and Vise Jaws (Machinable Soft Jaws)

    ON EDIT:
    As mentioned in a previous post to get an accurate indicator reading you need a straight and nearly perfectly round surface to measure against. I would suggest using a dowel pin. I have several sizes from McMaster On a chuck this size I would use a 1" x 3" long dowel. They are round within .0003", and cost less than $8.00.

    McMaster-Carr

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    Quote Originally Posted by vicfi View Post
    Looking into getting a bison chuck but having trouble finding a finished back plate.
    On the off-hand chance you find a finished back plate, you will still have to finish it. Part of your current problem may be that the PO found a finished back plate and just used it. Every spindle is a bit different and a new back plate must be mounted and finished on the lathe you intend to use it on to get it to run true.

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    I am working on chucks right now, a reasonably true running scroll chuck is valuable in hydraulics work, but , the chuck must be maintained to run .002" or better by grinding the jaws in the machine, and possi bly doing machine work on the chuck it self.
    Right off, the chuck in the video is a cheaply made import and not worth the time to fiddle w
    I know that by the way the chuck is built. Good chucks split right down the middle of the adjusting pinions. The import shown, has a back plate that holds the guts in, bad design for that size of chuck.
    just the way it is.

    Bison 12" showing the two body halves, better design. relatively easier to repair wear arears such as the scroll pivot.


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