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single point threading unsuccessful, any pointers as to where I went wrong?

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  • single point threading unsuccessful, any pointers as to where I went wrong?

    I watched videos, read threads and thought I had it figured out but no dice.

    Pics of the failed attempt.



    I had to cut it off with a hacksaw.

    pics of the set up






    The thread gauge fits like a champ




    I mic'd the OD and mine is .002 under the one from the hardware store.

    I chamfered the leading edge and the hardware store nut screwed on about halfway then it felt like it was binding.

    Under magnification 10x a see a ton of tiny tears in the metal so I thought its probably a rough surface and though screwing on the nut with a wrench would clean it up.

    I got about one full turn of the wrench and no more, not forward, not backwards, nothing.

    I advanced the tool into the work using the compound.

    I would appreciate any thoughts as to where I messed up.


    Thanks, Jim

  • #2
    You need to keep taking cuts until the nut fits.

    Rough tears are a function of the material, tool sharpness, lubrication, rigidity, etc. This a seperate issue to the fit.
    "...do you not think you have enough machines?"

    Comment


    • #3
      Nut appropriate for the thread? Metric nut and imperial thread? Will another nut thread on to what remains? Oil the thread before putting another nut on.

      Comment


      • #4
        There are others here who are a lot more experienced, but here is my $0.02 mostly questions. What type of material is it. Is the tool sharp. Is the tool above or below centerline, this will be much worse depending on how far out from the chuck you are trying to thread. I have had small stock crawl up the tool bit and tear metal off. Try resharpening the tool and turning the compound on 29deg and advance the cut into the thread about 0.015 at a time... I aways use a light cut for threading as I am just not that good at it, and my old lathe is really worn near the chuck. If possible use a die for anything less than 1 in dia...



        If it ain't broke, it ain't mine.

        Comment


        • #5
          I usually finish with one or two spring cuts.

          Comment


          • #6
            if you're going to have it stick out that far, cenetr dill the end & hold it with a dead or live center.
            gvasale

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            • #7
              For a thread to fit not only does the OD have to be correct, but so does the the mean diameter.

              There is several ways to get there.

              1 Keep taking a bit off until the nut fits.
              2 Finish of with a die set to a known matching bolt
              3 Measure using thread wires and a mic or with a thread mic.

              Have another go, it will work

              Steve

              Comment


              • #8
                It really sounds like the wrong nut was used. I've had almost identical problems before when using a nut that was almost the same. A 22 TPI where it should have been 24TPI for instance. There is enough slop in the threads that the first few will work, then when enough threads are engaged they tolerance will be used up and it will seize. I'm assuming that was not the case here.

                I can't tell from the pictures. Did you use a sharp pointed tool, or did you use one that had the appropriate radius for the specific thread? The major diameter of the screw can be perfect, but if the root of the groove is not deep enough the crest of the nut will rub on the root, eventually galling and sticking.

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

                Location: SF East Bay.

                Comment


                • #9
                  Are you cutting dry?

                  Try cutting fluid.
                  Alex

                  Comment


                  • #10
                    Hi all

                    "I usually finish with one or two spring cuts".... Just to keep me in the loop! What is a spring cut?

                    Regards...Bert

                    Comment


                    • #11
                      Originally posted by gvasale View Post
                      if you're going to have it stick out that far, cenetr dill the end & hold it with a dead or live center.
                      gvasale nailed it. As a rule of thumb your work should stick out no more than 3X the dia without support, typically a dead or live center in the tail stock. Other factors include type of material of the work piece and the cutting tool, wet or dry, tool sharpness, set-up accuracy, etc.

                      If you do not have a copy of South Bend's "how to run a lathe" order it immediately. Lots of knowledge in that book about threading and other lathe operations. Also buy a copy of Machinery's Handbook. A used one off FleaBay will more than suffice for the HSMer. Get your specs for threads, and lots of other stuff, from MH.

                      Comment


                      • #12
                        I hope you just have that much hanging out for setup. Even then I wouldn't do it. If you have more than your thread length hanging out of the chuck you should really have a center holding the end, lots of spring there. Otherwise you're going to really have to baby it along. If you move your thread gauge up does it still fit nice? My guess is the thread is tapered if not it may just be the rough finish. Another test would be to run a die up it and I think you'll find it cuts more as it goes.

                        Finish can be impacted by tool geometry, depth of cut, fee, speed, material being cut and the cutting lube used. If you're new threading try to get some 12L14 or even better 1144 which cuts like a dream. Trying to thread plain old cold roll steel isn't a good place to start. Nasty stuff to thread. Also running a file over the thread will knock the sharpness off.
                        Mike
                        Central Ohio, USA

                        Comment


                        • #13
                          Originally posted by mygrizzly1022 View Post
                          Hi all

                          "I usually finish with one or two spring cuts".... Just to keep me in the loop! What is a spring cut?

                          Regards...Bert
                          A repetition of the previous cut without advancing the cutting tool. Its done to negate the "spring" in both the tool and the work piece.
                          Last edited by Ohio Mike; 12-24-2012, 05:51 PM. Reason: typos
                          Mike
                          Central Ohio, USA

                          Comment


                          • #14
                            Originally posted by mygrizzly1022 View Post
                            Hi all

                            "I usually finish with one or two spring cuts".... Just to keep me in the loop! What is a spring cut?

                            Regards...Bert


                            AKA free ride in which a 2nd, 3rd etc pass is taken without advancing the tool. Used to take the spring out of the work piece that is induced by the cutting forces.

                            Comment


                            • #15
                              The thread LOOKS fine..... I'm not so sure I would call it a "failed attempt". Looks technically executed quite decently as far as the cutting and result is concerned. Measurement obviously is the final arbitrator.

                              The errors left are diameter, possibly a taper issue, or thread pitch, possibly an issue with the sharp V where the tip gets a burr on it that can jam up. Flank angle looks symmetrical.

                              It would not have much taper from sticking out that far.... there would be taper, but it's so far that the taper should be small angle-wise (and it should have been almost impossible to do the cut).

                              presumably it was NOT sticking out. I'm still not convinced taper is an explanation, a shallow taper takes some distance to bind.

                              A straight diameter issue should have refused to take the nut even that far.

                              A thread pitch mismatch is a good chance..... right diameter, but slightly wrong pitch. Since the gage fits, then assuming the gage is OK, the screw thread is fine for pitch. That leaves the nut.

                              I suspect a mis-match of thread and nut. Maybe nut is metric? I see the gage has "SAE" on it, so it is presumably what you wanted pitch-wise.

                              Above is barring some sort of swarf getting caught in the threads (possibly attached "fuzz"),
                              1601

                              Keep eye on ball.
                              Hashim Khan

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