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Thread: Acceptable Runout for a 4” Lathe Chuck?

  1. #1
    Join Date
    Oct 2008
    Location
    DC Metro
    Posts
    189

    Default Acceptable Runout for a 4” Lathe Chuck?

    So I bought some goodies on ebay, including a 4” 3 jaw lathe chuck with an R8 adaptor to use in my Bridgeport. Well, the retarded chimp that I bought the stuff from (I’m temporarily withholding names till I see if he makes any real effort to fix things otherwise, I kind of doubt it based on my experience with him/the company so far) took everything, chucked it in a flat rate USPS box with no padding between individual boxes/items to keep them from moving, opened the 4” lathe box, took the top foam packaging/padding out of it, bolted the R8 adaptor on it crooked, left the packaging out and folded the box flaps around the R8 stem which smashed the rest of the contents in the box in the process of getting to me. (the outside box got to me fine with no significant marks on it, but everything inside it is mangled, even the chuck box ended up with a big hole in the side of it and all it’s parts were scattered around the inside of the USPS box)

    Anyway, first I put it in my bridgeport and checked it with a dial indicator- it’s .047” out… grrr… I can actually see daylight between one side of the adaptor and the back of the chuck, and not the other.

    I took and loosened the mounting screws from the backing plate/adaptor to the chuck and carefully tapped it loose, cleaned up the burrs made whoever slapped this thing together, cleaned everything , made sure the mounting faces were as good as they were going to get and put it back together (and noted that either that either the treaded holes in the back of the chuck or the holes in the adaptor plate are miss drilled, and when you line one up the other 2 are a little off, also one of the recessed holes in the adaptor piece is not drilled as deep as the others so one of the allen cap screws sticks out a little). Anyway, I went back to the Bridgeport and dial indicator:

    Measured at the R8 adaptor flange: less than .001” runout, the needle just barely wiggles as it goes around.
    Measured at the machined side of the chuck, about 2/3 of the way down, between the adjusting head and the grooves that the jaws ride in: right around .004” runout
    I chucked up a polished steel round that I know is pretty good and chucked it up and loosened and did it again 3x (and then had to go to work) and got:.007”, .004”, and .004”
    (I don’ t know what the deal was with the one .007” reading, it shouldn’t have been dirt, I’m hoping that it’s not a sign that the jaws aren’t repeatable …)

    So I know that part of the answer here is “well, how accurate do you need it to be?” but realistically, how accurate can I expect average new parts like this to be out of the box? I was hoping for better than .002”, but I don’t know if that’s really realistic.

  2. #2
    BillH Guest

    Default

    For a huflungdung chuck, .004 to .005 is average. Bison is a little better. You want better? use collets or a 4 jaw.

  3. #3
    Join Date
    Aug 2005
    Location
    shreveport La
    Posts
    2,674

    Smile

    Quote Originally Posted by BillH
    For a huflungdung chuck, .004 to .005 is average. Bison is a little better. You want better? use collets or a 4 jaw.

    Yes I agree 100%

  4. #4
    Join Date
    Jul 2008
    Posts
    269

    Default

    .002? Not on a 3-jaw. Maybe on a brand new Buck or something equally expensive. You generally need an adjust-true type backplate to do any better. If any of my 3-jaw chucks stay within .005 I'm happy and it isn't unusual for older cruddier ones to be .020 out. The scrolls and jaws wear. The runout varies from place to place. Good in some spots, bad in others.

  5. #5
    radish1us Guest

    Default

    Hmm, me-thinks he is hoping for FAR TOO much, back up a little here, where did this chuck come from, ------- E-Bay.

    So you bought somebody's throw away el cheapo chuck, ask yourself this, why did they chuck it away ?

    YOU WANT ACCURATE, THEN PAY FOR IT.

  6. #6
    Join Date
    Nov 1999
    Location
    SE OZ
    Posts
    2,010

    Default Chuck spec sheets

    Mark.

    These pics are scans of the specs that came with a 125mm (~5") and 80mm (~ 3 3/16") Chinese chucks that I bought recently. The chucks were either on or within spec and work really well.

    The dimensions etc. are metric.

    0.04mm ~ 0.001"

    As long as the chucks are to spec, run-out is not a concern as my chuck - as it seems does yours - mounts directly to the lathe spindle flange. I have about 3 to 5 thou radial "play" and use a bronze "dolly" to "adjust" my run-out (a sort of, but very effective "tap-true") process and then tighten the chuck up. If the job doesn't require any great accuracy as regards initial job run-out I don't always bother with the "adjustment".

    I hope this helps.




  7. #7
    BillH Guest

    Default

    Quote Originally Posted by lane
    Yes I agree 100%
    Thanks for qualifying my opinion.

  8. #8
    Join Date
    Jun 2002
    Location
    Ashland City, TN
    Posts
    2,295

    Default

    For what it's worth, I was always taught that the 3 jaw was for convenience of rapid chucking and the 4 jaw was for dead on accuracy. So is a collet set.

  9. #9
    Join Date
    Nov 1999
    Location
    SE OZ
    Posts
    2,010

    Default Perhaps

    Not quite Al.

    The 3-jaw is for convenience as you say. It is also for gripping anything that is round or has a number of faces that is a multiple of 3 - ie triangular, hexagonal etc.

    The 4-jaw is more accurate but is better suited for rough surfaces and/or irregular shapes or anything (mostly) not suited to a 3-jaw chuck.

    Collets while better as regard accuracy without any further adjustment may be limited as to how far the job to be gripped can vary or deviate from the collet nominal size (R-8, C5 etc.) but the ER series have a gripping range capacity of 1mm (~0.040").

  10. #10
    Join Date
    May 2008
    Location
    Quadra Island, BC, Canada
    Posts
    313

    Default

    You may find you can get better results if you unbolt it from the adapter and try moving it round one hole, then bolt it up again and re test. I'm guessing there are 3 bolt holes, so you have 2 more chances at improving the run out.

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