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Acceptable Runout for a 4” Lathe Chuck?

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


    • #3
      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%
      Every Mans Work Is A Portrait of Him Self


      • #4
        .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
          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 ?



          • #6
            Chuck spec sheets


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


              • #8
                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

                  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
                    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.


                    • #11
                      I just got a new in the box Bison 8" 3-jaw. Only problem, they dropped it on the back and bent 2 pins. I've been looking for a top-line chuck that I could afford in this range, so I hopped on it. In checking it out, various locations on the spindle, and using various pinions, clamping different diameters of TGP rod, it consistently came up with at most 0.006 TIR. And using the "0" pinion in the best mount position yielded pretty consistent results within about 0.0018 and 0.0024 measured TIR on a high quality tenth indicator (no temp control or anything, but that's the numbers indicated). There were a few outliers, but reclamp back in same location was near dead-nuts the same every time. Most measurements were taken near the chuck, but changed very little at 3-4" out (don't recall exactly, but not enough to care). There were a few "outliers" that I couldn't account for, but only by a thou or so at most. I must say I am VERY happy with this chuck (not an Adjust true by the way).
                      Master Floor Sweeper


                      • #12
                        BadDog that's awesome. My 17 year old Bison 5" 3 jaw has .002 TIR.
                        Location: Jersey City NJ USA


                        • #13
                          My chinese chuck has no more than 5 thou, have not checked it often


                          • #14
                            Thanks for all the responses guys.

                            I guess I was expecting more than I should have been. For those of you that missed it the first time, it’s a new chuck that I bought on ebay. Where it was made… who knows, I can’t find any labels on it. To be honest, if this was for a lathe that I was hoping to do some good work with I would have never considered buying a chuck this cheap, but this is a “lets see if I can rig something up on my Bridgeport” experiment.

                            Oldtiffie, looks like where I’m at I’m well within the tolerances of those instructions that you posted now (though I’ve only actually measured it in a few of the “a” positions on those diagrams, none of the “b” positions), and based on everyone else’s feedback I guess I should be happy where I’m at.

                            One thing that was mentioned, to get it close and then tap it into position and tighten the screws… the back of the chuck has a recess and the R8 adapter has a matching shoulder that fits _REALLY_ tight. I can take the screws out of the back and it will not come off, I couldn’t pry it off. It took a good deal of careful hammering to get it to move off the less then 1/8” high shoulder. I’m sure no amount of tapping with the screws out would change the radial run out significantly. That actually involved part of my thought process… I was wondering if somehow loosening that fit slightly (maybe a little emory to get it so I can move it and then some valve grinding compound or something like that), but now I’m wondering if that might be a big mistake.

                            I guess I’ll try to see if the jaws are repeatable and I might try mounting it in the 2 other positions and see which one is the best…


                            • #15
                              Even if you have a high accuracy 3 jaw chuck, if you aren't careful to use it gently the scrolls will get sprung and even with good care they wear, both will cause the level of accuracy to drop.

                              A chuck with poor concentric accuracy will do a good job if you use it the way it was intended to be used.
                              The shortest distance between two points is a circle of infinite diameter.

                              Bluewater Model Engineering Society at

                              Southwestern Ontario. Canada