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Single pointing internal tapered pipe threads

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  • Single pointing internal tapered pipe threads

    A somewhat interesting job, with a small lesson in using a taper attachment.

    One idiosyncrasy of using a taper attachment on a manual lathe is that the feed direction should always be such that the stroke of the tapering feed should always pull the tool into the cut to counteract the ever present scourge of backlash. If it is possible to take heavy enough cuts to keep the backlash pulled out with tool pressure, this is a moot point. However it is always depressing to be making a beautiful, smooth taper when taking the roughing cuts and then have it turn into a stairway as the finer finishing cuts are attempted.

    With this in mind, what would be your guess as to how to orient a pipe flange to cut internal tapered threads?

    The problem being that the big end of the threads should be accessible for testing with whatever gage is to be used. Meaning the big end has to face away from the chuck.

    Further assuming that such threads are of the "right hand" variety, it becomes apparent that the spindle must run in reverse, with the tool cutting on the far side of the hole. This allows the taper attachment to pull the tool into the cut, thus keeping the backlash gremlins at bay.

    The photos may do a better job of explaining.


  • #2
    Have a look at a Youtube video by Keith Fenner titled Between your boxes , it will show a similar albeit smaller thread cutting job with tapered pipe threads.



    • #3
      why not use the compound?


      • #4
        Um, because the compound is not driven by the leadscrew, and turning the crank by hand at the proper speed to cut a uniform thread of the proper pitch is too much to ask of most of us.
        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
          Engage the half nuts and the X-feed at the same time?


          • #6
            The pull would be for OD turning. For ID turning, the need becomes for the tool to be pushed. I recall doing internal tapered pipe threads in the dim past with no difficulty other than taking the usual precaution of engaging the feed far enough away from the work to allow all backlash to be taken up before the tool engages the cut. Having a VFD is an advantage here as you can wind the carriage several inches past the work and return by feeding at a higher rate than that used for the cut.

            As with external tapered pipe threads, the cutting tool is at 90* to the work, not to the angle of the thread.
            Jim H.


            • #7
              i had a moment of stupidity, sorry.


              • #8
                Huh?I single point 10"-8 and 12"-8 NPT regularly and never have a problem.Maybe it's a difference in cross slide/taper attachment design?But then like JC says I always pull or push as need be the backlash out and use some over travel to get the taper attachment averaged out too.
                I just need one more tool,just one!


                • #9
                  Wouldn't be stupidity on my second lathe, dian. My feed goes to the top slide. I admit that I'd have two small problems. One, I'd have to calculate the feed on the diagonal rather that along the bed, and two, because of the angle I'd get a little non-linearity from the CV joints. I'm sure the thread would be useable at such a small taper, though. Maybe a little harder to seal if there were two high spots each rev !
                  Richard - SW London, UK, EU.


                  • #10
                    I don't know about your lathe, but on mine the longitudinal and cross feed controls are separate and can't be engaged simultaneously. Be a good trick to set them up for the right feed on each direction though. Bob.


                    • #11
                      On my Hendey you can engage the carriage and cross feeds at the same time,
                      and the net result is 45 degrees. Then you can set the taper attachment to
                      add or subtract from 45 deg to set your desired angle. There is a video on
                      youtube with a Hendey T&G showing this being done.