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threading to a shoulder

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  • threading to a shoulder

    how on earth do you do it?
    i can get really close, but inevitably,
    if i try to get all the way to the shoulder, i either damage the work or break my tool.

    tips? hints?

  • #2
    Get up real close. Turn off lathe. Turn the chuck by hand. Works for me.
    Lynn (Huntsville, AL)


    • #3
      Use a thread relief groove, thread away from the shoulder with the tool upside down (be careful to take up backlash), finish the thread with a die, or use lynnl’s way. You can also retract the tool with the compound instead of the cross slide. This withdraws the tool away from the shoulder. I assume you are running at your slowest possible speed.
      Location: North Central Texas


      • #4
        As others have suggested....

        Also, if the thread really, absolutely has to "disappear" into the shoulder, think about
        drilling/tapping the piece and Loctiting in a threaded rod.

        Or redesign the part so you don't need to thread right up to the shoulder.
        Try to make a living, not a killing. -- Utah Phillips
        Don't believe everything you know. -- Bumper sticker
        Everybody is ignorant, only on different subjects. -- Will Rogers
        There are lots of people who mistake their imagination for their memory. - Josh Billings
        Law of Logical Argument - Anything is possible if you don't know what you are talking about.
        Don't own anything you have to feed or paint. - Hood River Blackie


        • #5
          I had an "engineer" draw a bunch of shafts for a machine that was being built that way, I had 1/8" clearance from where the thread ended and the shoulder. Thankfully there was relief. What I did was mount the tool upside down, turn the spindle backwards and thread towards the tailstock. Leave the split nut engaged and jog back to the starting position. This way works best with a lathe that has a clutch drive. There's no reason why you can't just engage and disengage the split nut, but on our lathe someone stripped the gear that rotates that handy dial.



          • #6
            In a similar vein to the threaded rod idea, you could also turn the shoulder back acouple of threads and thread as far as possible into a relief groove. Then make a collar that is the thickness of the extra threads, tap it, and install it with Lock-Tite to bring the shoulder back to the proper position.

            But why does the thread have to go all the way to the shoulder? The mating part can simply have a relieved area for a couple of threads, can't it? That would be a lot easier.

            Paul A.
            Paul A.
            SE Texas

            Make it fit.
            You can't win and there IS a penalty for trying!


            • #7
              Super Dave


              • #8
                Tracer lathe works too.
                Set the slide at 30 degrees and feed up to an L shaped template.

                Or, you could countersink the mating part.



                • #9
                  I do my own barrel work and thread to the barrel shoulder all the time, within .050 to .075 of it. What I do is once I have everything setup, I mount a 2" travel dial indicator on the ways and let it ride on against the saddle. It is set to zero right where I want to end the thread. Once you engage the half-nuts and are threading, just watch the indicator return to zero, then disengage/back out cross slide at the same time. Never hit the shoulder yet. (Knock on wood)!


                  • #10
                    thanks everyone for the input.
                    gave it a try today and it wasn't too bad.. my lowest speed allowed me unwind the crosslide pretty fast (relative to lathe speed) ... and i made it right up to the shoulder with no nicks or dings.

                    it was a small thread.. large diameter.. probably 37mm diam x 1mm pitch.. so i had some room to breath.

                    i turned out a little "bottle" .. like those steel nissan thermos bottles. i got the idea to put an oring into the (face of) the shoulder.. so threading the cap on would create a seemless bottle and the body would seat against the oring in the lid.. instead of having the oring inside ie concentric to the two mating threads.

                    probably no good for a thermos.
                    but it sure looks nice and shiney.

                    i love the way it screws together and mates seemlessly.

                    thanks again,

                    ps.. i like the 'turning the last thread by hand' tip.


                    • #11
                      ps.. it helped to make a new small thread cutter from an HSS cutoff blade. i put the 60deg tip on at a 30deg offset.. so there was less danger of running into the work.

                      i usually use large HSS bits for threading.. 3/4" x 3/4" .. invariably resharpening tends to move my tip / cutting edge further to the right.. towards the tail. leaving a big meaty shoulder towards the chuck just ITCHING to get a bite of the work.