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3 Jaw Chuck Issues

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  • #61
    I blued and then lightly stoned the mating surfaces of the spindle and the mating inside diameter of the chuck. This removed any possible burrs and embedded materials, and when I reassembled the chuck to the spindle, I checked chuck runout once again, and still have .003" total indicated runout on a 1" diameter test rod held in the chuck jaws. I have one thing left that I can check, and that is the mating face of the chuck. I have had issues with the three studs which are screwed into the back of the chuck plate, and there is a very small possibility that I raised some of the material around one of the studs. I will check and see if I can slide a 0.001" feeler gauge between the spindle flange and the chuck flange.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • #62
      I have found something!!! I can slide a 0.0015" feeler gauge in between the chuck flange and the spindle flange on almost 125 degrees around the spindle circumference, with all the bolts which hold the chuck in place bolted down. That indicates that the centerline of the chuck is not in plane with the centerline of the spindle. I will now disassemble things one more time and dress the mating face of the chuck.
      Brian Rupnow
      Design engineer
      Barrie, Ontario, Canada

      Comment


      • #63
        That ammount of runout is about the normal expected runout for a three jaw scroll chuck. You could try tightening the bar using each of the keys in turn to find which one gives the best results. Make a small mark so you can always use the same one. There is no guarantee that when holding different diameters of work that the runout will stay the same.
        If you have a surface table, you could rub the mating face of the chuck on a sheet of 400 wet and dry paper. if you sprayed the paper with a little WD40, there would be no danger of abrasive dust getting in the works. Then just wipe the rear of the chuck before remounting it. If the gap remains, it will be the face of the lathe spindle being convex. A tiny skim would sort that out.
        Last edited by old mart; 11-23-2020, 02:24 PM.

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        • #64
          3 thou is pretty good. It should stick on the taper when loosened, it is effectively a press fit.
          21" Royersford Excelsior CamelBack Drillpress Restoration
          1943 Sidney 16x54 Lathe Restoration

          Comment


          • #65
            After loosening the 3 nuts which hold the chuck to the spindle and retightening in different sequences, my total indicated runout changes a bit, but only a very little bit. I got things to the point where a 0.0015" feeler gauge wouldn't slip between the chuck and the mounting flange on the spindle. So---I googled "acceptable runout in 3 jaw chuck" and it seems that .003" total indicated runout is acceptable, .002" is better, and .000 happens so rarely that if you get that reading you should rush right down to the store and buy a Lotto ticket. I have ordered 3 new studs, and when I remove the old studs from the chuck I will stone the back side of the chuck before screwing and Loctiting the new studs in place. There is no taper on the spindle nor in the chuck where they attach. Both surfaces are parallel.
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

            Comment


            • #66
              Don't loctite the studs in. They need to float.
              21" Royersford Excelsior CamelBack Drillpress Restoration
              1943 Sidney 16x54 Lathe Restoration

              Comment


              • #67
                Originally posted by The Metal Butcher View Post
                Don't loctite the studs in. They need to float.
                X2 on that is your Lathe a CX 707 if so it’s a D 1-4 mount.

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                • #68
                  How can a 10mm stud threaded into a 10mm hole float? My lathe is a CX701.
                  Brian Rupnow
                  Design engineer
                  Barrie, Ontario, Canada

                  Comment


                  • #69
                    Do the wiggle? Yes. Or they should. The allows the cams to pull them up the best. The cam will probably break the bond if it's not perfectly aligned. There is no reason to loctite them. They can't back out when clamped, and they can't move when on the bench due to the lock screw. Zero reason to loctite them, and plenty not to.
                    21" Royersford Excelsior CamelBack Drillpress Restoration
                    1943 Sidney 16x54 Lathe Restoration

                    Comment


                    • #70
                      MetalButcher--Somehow you and I have a great disconnect here. The studs don't wiggle. There are no cams. There is a non tapered nose on the spindle which fits into a non tapered hole on the back of the chuck. This is what ensures concentricity between the two parts. There is a flange on the spindle with 3 eleven mm holes in it at 120 degrees apart. Three studs which are more or less "permanently" screwed into the back of the chuck fit through the three 11 mm clearance holes on the spindle and have nuts and washers on them. That ensures that the chuck doesn't part company with the spindle.
                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

                      Comment


                      • #71
                        Originally posted by brian Rupnow View Post
                        How can a 10mm stud threaded into a 10mm hole float? My lathe is a CX701.
                        Originally posted by brian Rupnow View Post
                        MetalButcher--Somehow you and I have a great disconnect here. The studs don't wiggle. There are no cams. There is a non tapered nose on the spindle which fits into a non tapered hole on the back of the chuck. This is what ensures concentricity between the two parts. There is a flange on the spindle with 3 eleven mm holes in it at 120 degrees apart. Three studs which are more or less "permanently" screwed into the back of the chuck fit through the three 11 mm clearance holes on the spindle and have nuts and washers on them. That ensures that the chuck doesn't part company with the spindle.
                        My mistake Brian. There is a great disconnect. I I thought you had a model with a camlock spindle. I couldn't look it up at work on my phone. Very unfortunate to me that it's not a camlock. So basically you just have a fixed backplate. You may be able to "dial" in the chuck if there is any play on the register by snugging it and bumping it true before tightening. Carry on sir.
                        21" Royersford Excelsior CamelBack Drillpress Restoration
                        1943 Sidney 16x54 Lathe Restoration

                        Comment


                        • #72
                          Parallel fits by nature cannot be exact, or they would be more nearly press fits. There is always some radial play, and the issue is whether that is excessive and capable of causing the problem. The stud/bolt clearance has all the same issues with parallel fit, and my understanding is that the holes are normally made with a generous allowance of room.

                          So it may be a good idea to take a very good look at the fit of the chuck onto the spindle to see if there is any radial play in the system that might explain the issues found. The problem is of course what to actually do about it if some looseness is found. But at least the nature of the problem would be known.
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                          Hashim Khan


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                          • #73
                            Parallel fits work quite well to give concentricity IF the mating flange surfaces are perfectly flat. However, if a "burr" has been raised around one of the studs where it screws into the chuck, you can crank all three nuts down tight, and still have angular disparity between the centerline of the spindle and the centerline of the chuck. Since these studs are not hardened, I have messed them up somewhat switching between 3 jaw and 4 jaw chucks. I have ordered 3 new studs, and after I remove the three existing studs I will "stone" the mating side of the chuck before putting the new studs in.
                            Brian Rupnow
                            Design engineer
                            Barrie, Ontario, Canada

                            Comment


                            • #74
                              Three jaw self centering chucks are not suitable for reliably holding material or parts concentrically.
                              Sometimes they may do so but that is a matter of luck
                              Certainly some are better than others, some when new.may hold workpieces within a couple of thous or even less.
                              They possess the advantages of speed in set up and versatility to hold varying sizes simply by a few turns of the key.
                              Every good textbook I have ever read , and all the experienced lathe hands I have worked with have agreed that if you want to hold material or machined parts truly you need either chucks where the jaws can be adjusted individually or collets.
                              (I know of the set true 3 jaws. but they usually set true only at the diameter they are set for)
                              I once had a 3 jaw independent, that was a nightmare to use and it quickly went away!
                              Chasing rainbows can be fun, but if you want quality parts all the time a three jaw self centreing chuck is NOT the tool for the job.
                              Regards David Powell.

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                              • #75
                                David--You're not wrong. Be that as it may, I have built 40 working model engines using primarily my 3 jaw chucks. Sometimes I have to use a four jaw chuck to make an eccentric or something which requires an offset. It seems that model engines are tolerant of .003" tir. Occasionally I think of using collets, but then I look at the price of a quality collet set, and that quickly makes me more tolerant of .003" tir also.
                                Brian Rupnow
                                Design engineer
                                Barrie, Ontario, Canada

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