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lathe spindle question

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  • lathe spindle question

    My neighbor just got a small lathe. He is so proud of it. I am glad for him except, the spindle seems to be out. I say seems because the 3 & 4 jaw chucks are out better than .025" - .040". We took the spindle out and put it up in the 4 jaw of my big lathe. I got it to .0004". This is at the front bearing spot and also checking the front of the spindle bore, both no more than .0005" out. I put both chucks on the small lathe I have. The 3 jaw is .006" out and the 4 is .001" out. I figure from that the chucks are ok. The spindle holds the chucks ok, but turns out of round as well as tips front to back. I wondered if the spindle registration point could cause this problem. It is out .001" on the face. The threads look ok but they sure seem to be out.
    Anyone have any ideas? Thanks.

  • #2
    I finally saw the spindle was soft. This ment I could chase the threads, which I did. The threads were rolled just slightly, enough to throw the chucks off. I got it true to .0006". We put it back together and now both chucks tir is .002". The back bearing must be off .001" or so. It should be fine for whatever he may need to do.


    • #3
      Glad you could solve the problem and help him out. .002"? That's just about as close as I can hold it!!!


      • #4
        I was glad to help him. He was impressed that this type work could be done outside a factory. I sort of thought that was one of the reasons he bought the lathe. It turned out, he thought you could only turn stuff. He never even thought of being able to thread or center stuff to .001. I mean his tolerance is + or - 1/4". This was kind of a shock for him, but he is sure happy!


        • #5
          Some one post chip a link to "rollies dads..... " method of aligning (or checking alignments of axis (axi?). There were a lot of links.

          I dont think the threads on the spindle have much to do with holding the chucks in line. Isn't it the unthreaded spindle behind the threads and the square shoulder the chuck fits against? And .001 run out at the reister area could easy make several times that amount of wobble at he chuck face.

          I think I am confused!!!! BUt Chip has done his good deed! santa will smile .


          • #6
            Thanks Steve,
            I am pretty sure it was the threads for the biggest part. After I chased the threads I put the chuck on and tir was .005", istead of .030". Then I turned and faced the spindle register area. It made to where we were only out .002" after assembly. I'm just glad it worked out for him, Rick.


            • #7
              There have been a bunch of arguments about what alines the chuck. I think it is a matter of religion.....

              But, if the register is off, the threads will cock the chuck. And, the register is usually undersize at least a couple thous, just so you can get the chuck on, or from wear, etc. So if that were so critical, why wouldn't the chuck always be out as much as the register allows?

              The threads look like a cone to me, I would think they aline in combination with the shoulder.

              Here is some more:


              • #8
                OSO: I suspect you are correct. When I said .0001 at the register I should have said shoulder, because I think the shoulder truely holds the chuck or whatever perpendicular to the spindle. I never really thought about the purpose of the register portion.
                I instinctively feel that if the spindle at the register is, for example, 1.495" that the chuck back should be 1.495+ just a smidgen (RCH to be precise). From what the chaski link says, itmakes no difference. so I guess is spent my efforts for naught. My thinking was that the maximum run out would be half the difference in diameters of the chuck back and the spindle. This would be back plate run out not chuck body run out.

                Question for you shop teachers with several lathes (threaded spindle)- Do chucks interchange from lathe to lathe with no loss of concentricy? if the shoulder andthreads do the aligning, they should interchange.

                I stay confused when i think just a little bit


                • #9
                  I was confused on this topic, having studied many postings on what provides the best chuck alignment. Recently, I purchased a new 5" Bison 3 jaw direct mount for my old Maximat 7. The thread is 1.5" x 8 tpi and the registered area measured 1.5000 on my spindle and 1.5005 on the chuck. The chuck threaded on smoothly and seated squarely. No gloat intended but on a 1" steel rod, 1.5" out, runout is +/- 0.0005 ... for now.

                  I suspect that while a well centered, accurate spindle thread is important, it is the fit and squareness of the unthreaded area and shoulder which matter most ... in my humble opinion.



                  • #10
                    The fit of the register, and the squareness of the spindle are what ultimately determine the accuracy of the fit of a threaded chuck.
                    The better the fit of the chuck and threads, the better chance of good alignment, but you cannot count on them pulling a 40 or 50 or more pound chuck into alignment.
                    All other arguments aside, why do manufacturers bother to continue to make their chucks and lathes with a register, and call it a register if it is not there to register something?
                    That being said, if your main concern is accuracy, you should be using a four jaw chuck anyhow.
                    Jim H.


                    • #11
                      NHENG, Only .0005" out? Man! That's a heck of a lot closer than these old eyes can see the dials on my old Logan!! Treat it as a precious possession!!


                      • #12
                        HCH: Until some one who has a multitude of simular lathes and a like number of chucks, says they have tried swappping and see no difference, i am going to continue to try for a very close fit. I agree that independent jaws are key to accurate positionings, but if a person can tell a differnce between a 3 phase motor and a single phase in the surface finish, they should be able to see the results of 30 pounds of rotating mass, a few thousands off center. Of course, for centered work, I guess the jaws have to move over and help counter balance the off center mass . Some times I think there must be witch craft involved when people work to less than .001 with no filing, polishing, cusssin', or seat !


                        • #13
                          Steve, I was saying that the fit of the register is what determines the accuracy of the chuck. The closer the fit, the better. For best accuracy, the backplate, less the chuck should be very carefully fitted to the lathe spindle, aiming for the best possible fit on the register, +-0. Then face the back plate, and very carefully fit the chuck to the backplate. That chuck will fit that lathe, but may not be as accurate on another machine.
                          Accuracy of a three jaw chuck is dubious at best. The best chucks that have three pinions for tightening the jaws have one marked that is the master, used to tighten for the best accuracy.
                          As far as surface finish relating to motor phases, we'd best watch for moon phases as well. Probably have as much effect.
                          I have plenty of files and emery cloth, not about to get rid of them.
                          Jim H.


                          • #14

                            The question of the purpose of the register was covered in the thread at the link. Short story is that it starts everything off alined better than if it were just loose on the threads. For more, see the link.

                            Since no chuck I have has a good register, and all repeat nicely, I don't think it is essential. Bt they are not 50 lb chucks either.

                            I can vouch that a good register and bad threads won't aline at all, though.


                            • #15
                              JCH: you and I are on same wavelength. But I would like to hear from the shop teachers. Do you keep chucks (synchronized jaws) matched to lathes when the cheese gets binding?
                              I think a good long register (which does not exist so far as I know - at least on threaded noses) would hold the chuck in line very well, leaving the shoulder doing nothng more than keeping the chuck from sliding on further, and that a tapered cotter pin to stop rotation would make the chuck run with no wobble. I can't see that a 60 degree slope has much more lifitng power (to center things) than a 90 degree shoulder has. THe vectors are just too small for the forces involved. But as I say, I am easily confused. All I know is that you can't vote on the math nor the laws of physics- but I do misapply them often.