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  • "Off center" parts?

    Ok, so I'm working on a project..

    I turned two pieces of some 304 SS down to 0.40" holding the work in a 3 jaw chuck.

    I then center drilled and then drilled one of the pieces, using the tailstock chuck progressively up to an I drill, then tapped to 5/16-24.

    I then turned the end of the other down to .3125" and used a die to thread to 5/16-24.

    When I attempted to thread them into each other, they are not centered on each other. Not even close.

    I started looking at them closer and it looks like my tailstock may be out of alignment, as the hole I drilled is not centered in the parts. One is easily more off center than the other.

    Does this sound like a tailstock alignment issue or is something else going on as well?
    Last edited by bellyupfish; 12-05-2017, 10:17 PM.

  • #2
    That's not the tailstock, that's your chuck.

    allan

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    • #3
      Originally posted by kitno455 View Post
      That's not the tailstock, that's your chuck.

      allan
      Really?

      I guess I need to check that tomorrow.

      Comment


      • #4
        Could be the drill bit.

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        • #5
          Originally posted by Toolguy View Post
          Could be the drill bit.
          Well, I wonder which one it would have been? I used several, ending with the I on the side I tapped.

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          • #6
            did you center drill before drilling?

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            • #7
              Originally posted by A.K. Boomer View Post
              did you center drill before drilling?
              Yes.

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              • #8
                Originally posted by bellyupfish View Post
                Yes.
                3 Jaw self centering chuck, 4 jaw chuck?

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                • #9
                  Originally posted by reggie_obe View Post
                  3 Jaw self centering chuck, 4 jaw chuck?
                  3 jaw..

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                  • #10
                    I have learned to always register the parts in the 3 jaw at jaw 1. A scratch, punch prick, sharpie mark, whatever. If you load stock in the chuck at the same place it helps.

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                    • #11
                      Originally posted by softtail View Post
                      I have learned to always register the parts in the 3 jaw at jaw 1. A scratch, punch prick, sharpie mark, whatever. If you load stock in the chuck at the same place it helps.
                      What is the reasoning behind this? Sounds like a good idea, just for repeatability.

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                      • #12
                        3 jaws rarely index like you need. Use a 4 jaw if it's important.

                        For the method above, then can work for already turned stock., but if you are turn a smaller diameter then reversing the stock... good luck. Even worse if one end is mill stock.

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                        • #13
                          A 3 jaw DOES NOT REPEAT. Even if you think you put it back just like it came out, so that it HAS to be on the same center...... you didn't, and it won't be.

                          A 4 jaw has the same problem, but you can at least fix it with a 4 jaw, by re-adjusting to center the part.

                          If it has to be right, do it between centers.

                          BTW, a misaligned tailstock will NOT drill off-center, it drills oversize and probably bell-mouthed.

                          Turning between centers with a misaligned tailstock will create a tapered part.
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • #14
                            A three jaw scroll chuck is seldom perfectly centered. It may be off by several thousandths, depending on wear. Add to that the possibility that the stock was not perfectly round and you can have the stock quite a bit off center.

                            Now multiply by two, since you did two parts and each could be that far off.


                            But wait! It gets better! Threads are not a great way to center parts. There has to be clearance between the threads to avoid an interference fit. The way around that problem is to put a matching registration shoulder or bevel on each piece.

                            Dan
                            At the end of the project, there is a profound difference between spare parts and extra parts.

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                            • #15
                              Originally posted by J Tiers View Post
                              A 3 jaw DOES NOT REPEAT. Even if you think you put it back just like it came out, so that it HAS to be on the same center...... you didn't, and it won't be.

                              A 4 jaw has the same problem, but you can at least fix it with a 4 jaw, by re-adjusting to center the part.

                              If it has to be right, do it between centers.

                              BTW, a misaligned tailstock will NOT drill off-center, it drills oversize and probably bell-mouthed.

                              Turning between centers with a misaligned tailstock will create a tapered part.
                              Well that explains it then. I removed the work multiple times from the chuck. Better planning is needed.

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