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Thread: Piece wobbles in donut chuck

  1. #1

    Piece wobbles in donut chuck

    I just made a donut chuck. The chuck itself turns perfectly but once I attach something to it the work piece wobbles. I know it's because the piece isn't centered exactly. I've tried several times remounting with no luck.

    Thinking back I don't recall anyone that made a video of how to build one of these things show an actual work piece mounted and spinning. They probably have the same problem.

    It's good enough to remove what's left of the tenon, sand and apply a finish. But certainly not for final bottom shaping.

  2. #2
    Join Date
    Oct 2008
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    Kapolei Hawaii
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    3,236
    HoldFast makes an adapter, MT2 to the threads on your spindle. About 25 bucks when I bought mine. What this does, is aligns your piece perfectly in the donut chuck. All it is, is a MT taper that holds you chuck, that has your ALMOST finished piece in it, put it on the tail stock, snug up the tailpiece to the donut chuck. It CANNOT be off center. You can, (after 3 tries for me) make one, if you can thread pieces with your spindle size. Beall makes thread dies. It is REALLY hard to thread something EXACTLY centered. Spend the 25 bucks. I could sell you my home made one that is ALMOST centered and straight for 25 bucks... LOL

  3. #3
    Join Date
    Sep 2015
    Location
    San Diego, Ca
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    1,647
    For pieces that I can't chuck up, I have used (1) 18" dia. wooden faceplate with a half dozen cleats to hold the turning piece, (2) a set of cole jaws or (3) a vacuum chuck. On each of these I can have an issue with centering but I take the time to get it very centered.

    BTW, It really helps to leave a live center dimple for recentering. Also it helps to keep the live center pressed into the dimple when tightening down the donut chuck and even turning if that can be done. If you notice that the piece tries to shift when you are tightening the donut chuck, then perhaps you need to shim the inside of the donut chuck to adjust the forces to be equal. Like I have done with my wooden faceplace. Sometimes I have even used hot glue to hold a piece from moving laterally. If I work at it, I can routinely get the faceplate centered to within perhaps 0.010 ". I could probably do better if I needed to but that is rarely needed.

    Another thing to consider is to attach a "jam chuck" to the bottom of the donut chuck. If you remove the outer ring of your donut chuck to get access, you could turn your jam chuck to be perfectly concentric. Then push on your piece, then bolt on and tighten the outer ring of the donut chuck. It also helps, in this instance, to have a piece of foam around the inside donut hole to distribute the force and eliminate any marring. So in this case, the jam chuck would do all of the centering and the donut ring would only be used to keep the piece from flying off.

    If your donut chuck is very very solid (hard to do with extended pieces of all-thread, you could actually turn the inside of the ring to be perfectly concentric. But if the holes for the threaded rod are a bit sloppy, it won't hold that concentricity.

    Why don't you post a picture of your jam chuck and also the typical piece that you would want to turn. That was others could give you more specific advice.

  4. #4
    Join Date
    Mar 2016
    Location
    Elmodel, Ga.
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    798
    Another helpful hint is to draw circles on the head stock side of your donut chuck. I put mine about every 3/4" so that I have a reference as to where the piece is sitting. It helps tremendously.
    My Dad always told me "Can't Never Could".

    SWE

  5. #5
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
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    12,298
    Quote Originally Posted by Michael Costa View Post
    I just made a donut chuck. The chuck itself turns perfectly but once I attach something to it the work piece wobbles. I know it's because the piece isn't centered exactly. I've tried several times remounting with no luck.
    For precision alignment with some holding methods (jam chuck, vacuum, etc.) I sometimes use a dial caliper mounted on an adjustable arm. Tighten the holding method gradually while turning by hand and making fine adjustments. If everything else is right I can quickly align perfectly.

    If the base of the piece is still mounted in a chuck one of those threaded chuck adapters that fits in the tailstock works nicely. Nova makes one, as does Best Wood Tools and others.

    JKJ

  6. #6
    I have the circles drawn in the inner surface and I've tried a jam chuck with it as well. The jam chuck was kind of crude and I'm thinking of remaking this with the jam chuck from the beginning and not an afterthought.

    I also found steel T-nut type inserts (ACE hardware) with a sqaure hole to accept 1/4-20 carriage bolts. A one-sized donut chuck is relatively quick to make.

  7. #7
    Join Date
    Jan 2004
    Location
    Fredericksburg, TX
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    2,576
    Equal tightening of the hold down bolts can also help keep the piece centered. Also the type of soft pad on the face could be allowing the piece to shift and be out of balance. I find that normally the area being worked on when using the donut chuck to work on tenon area is small and close to center and a little wobble can be tolerated. Trying to work on the side would be another issue.

  8. #8
    If you sanded the bowl before putting it in the donut chuck then it is no longer perfectly round. The top ring of the donut will try to shift the bowl to get equal pressure all the way around. Making the base plate into a jam chuck and then allowing the donut ring to tilt and shift is more important than having the donut ring perfectly parallel to the base plate. It doesn't really matter if the foot of the bowl is perfectly concentric with the rim.
    Bill

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