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what's the largest TPI thread you've ever cut?

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  • what's the largest TPI thread you've ever cut?

    I cut a 64 TPI as a test today, and I can't imagine how people make use of the ability of lathes -such as monarch EE- that are able to cut 184TPI. I think the hardinge HLV can cut 224 TPI, why would you need such a fine thread (even in optics it doesn't make sense)

  • #2
    When they built the Synchrotron here in Saskatoon a few years ago, the leveling blocks for the light beam were built by a local machine shop. One of the shop owners was a brother to a friend I worked with who had been given one as a souvenir and he brought it to work. AFAIR, the threaded block was roughly 1 1/4" thick by 2 1/4" square, threaded completely through, and the "weight jack" part of it was about an inch, maybe 1 1/8" in diameter. I do remember that the tpi was 180 and it turned as smooth as anything I have every seen.
    Location: Saskatoon, Saskatchewan, Canada

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    • #3
      Originally posted by Arcane
      When they built the Synchrotron here in Saskatoon a few years ago, the leveling blocks for the light beam were built by a local machine shop. One of the shop owners was a brother to a friend I worked with who had been given one as a souvenir and he brought it to work. AFAIR, the threaded block was roughly 1 1/4" thick by 2 1/4" square, threaded completely through, and the "weight jack" part of it was about an inch, maybe 1 1/8" in diameter. I do remember that the tpi was 180 and it turned as smooth as anything I have every seen.
      Does adding more threads per inch increase or decrease the load capability for the bore sustaining?

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      • #4
        Originally posted by Elninio
        Does adding more threads per inch increase or decrease the load capability for the bore sustaining?
        You just struck a nerve This topic came up once before and the general consensus was that fine threads were stronger then coarse threads. There must be a cross-over point because I speculated that if you carried this theory out all the way you would end up with next to no thread depth and hence the bolt would fall through the nut. The thread ended abruptly as I remember and I was left holding the bag and feeling like a jerk
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        • #5
          Largest I have ever cut 8"- 2tpi,smallest 1.220"-72.
          I just need one more tool,just one!

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          • #6
            Coarsest, 2toi Buttress, finest. probably 64tpi. Although I did do some 5/16th-40 internal single point for some inside mic extentions.
            Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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            • #7
              Your Old Dog posed this with quote:
              Quote:
              Originally Posted by Elninio
              Does adding more threads per inch increase or decrease the load capability for the bore sustaining?


              You just struck a nerve This topic came up once before and the general consensus was that fine threads were stronger then coarse threads. There must be a cross-over point because I speculated that if you carried this theory out all the way you would end up with next to no thread depth and hence the bolt would fall through the nut. The thread ended abruptly as I remember and I was left holding the bag and feeling like a jerk
              But wouldn't it be the same as lowering the TPI to 0? I.e., they both become nonfunctional.
              Without going to extremes, i myself feel(no math here) that because of the surface area of large TPIs, they would be the stongest, with the added ability to make fine adjutments.
              __________________
              Last edited by Deja Vu; 09-15-2010, 11:16 AM.
              John M...your (un)usual basement dweller

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              • #8
                Fine threads may be theoretically stronger I don't know but I never had a problem with the bolts on my old chevy, nice course american threads.

                My suzuki samurai with metric fine threads is a different story. It's virtually impossible to remove a bolt and reinstall with out cross threading. Now I resort to chasing every thread with a tap knowing it will save me time in the long run.

                Just last week I single pointed some 6-48 screws for a scope block mount on the lathe. Smallest and highest pitch I've ever single pointed.

                I dropped one in the lathe removing it and never found it. Had to make another.
                Last edited by hitnmiss; 09-15-2010, 11:08 AM.

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                • #9
                  I did some experimenting with some high TPI threads once. At some point, you stop thinking about TPI and start thinking in terms of feed rate.

                  On high TPI threads the material becomes a real important factor. Many common (cheap) steel alloys will just have too rough of a finish and the actual thread disappears in the surface roughness. You need a clean cutting (leaded?) alloy or perhaps 360 brass. And real sharp tools. REAL sharp. I have done 64 and 72 TPI with a fair amount of care. Over 100 TPI would get harder but could be done. I am not so sure about 200 TPI: that is only a 0.005" lead. You would need a magnifier just to see it. Infeed would be only 0.004".

                  At 100 TPI and higher, I would definitely want to use a die to finish the thread. Probably better at lower numbers too.
                  Paul A.
                  SE Texas

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

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                  • #10
                    Better to use a differential thread adjuster, although that would be difficult in some optical applications.

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                    • #11
                      Originally posted by Deja Vu
                      But wouldn't it be the same as lowering the TPI to 0? I.e., they both become nonfunctional.
                      Without going to extremes, i myself feel(no math here) that because of the surface area of large TPIs, they would be the stongest, with the added ability to make fine adjutments.
                      __________________
                      I don't think the analogy works. Consider ratchet mechanisms - have you seen "one way ball bearings" ?

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                      • #12
                        Originally posted by Paul Alciatore
                        I did some experimenting with some high TPI threads once. At some point, you stop thinking about TPI and start thinking in terms of feed rate.

                        On high TPI threads the material becomes a real important factor. Many common (cheap) steel alloys will just have too rough of a finish and the actual thread disappears in the surface roughness. You need a clean cutting (leaded?) alloy or perhaps 360 brass. And real sharp tools. REAL sharp. I have done 64 and 72 TPI with a fair amount of care. Over 100 TPI would get harder but could be done. I am not so sure about 200 TPI: that is only a 0.005" lead. You would need a magnifier just to see it. Infeed would be only 0.004".

                        At 100 TPI and higher, I would definitely want to use a die to finish the thread. Probably better at lower numbers too.
                        My sharpened tool had no radius and it was barely enough for the 64TPI thread I cut, I sharpened it on a medium-grit 8" benchgrinder.

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                        • #13
                          When I read the subject line "largest thread" I thought of the
                          3 3/4" x .875 pitch L.H. Brown and Sharpe worm thread (similar to an Acme thread but different) I made some years back. I did it on the CNC lathe as no other lathe in our shop would make that coarse a thread. Because our CNC lathe will not allow one to feed toward the tailstock I had to make an adapter that let me mount the cutting tool on the back side of the cross slide, run the spindle in reverse and thread toward the headstock to make the LH thread. All in all a very interesting project.

                          It was a repair job for a friend who is active in the Punkin Chunkin contests and
                          was used in the winch they used to haul back the draw string of their ballista.

                          Then I re-read the line and realized that you meant the "finest" thread you ever made. oops.
                          Errol Groff

                          New England Model Engineering Society
                          http://neme-s.org/

                          YouTube channel: http://www.youtube.com/user/GroffErrol?feature=mhee

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                          • #14
                            stronger thread?

                            At the risk of side tracking the thread, I would add that IMHO the coarse thread is used for strength and the fine thread for power. For example if you look at a stud used in an aluminum cylinder head you will see both fine and coarse threads. the coarse end is threaded into the aluminum and the fine thread is fitted with the nut. this provides strength (shearing) in the aluminum given a larger cross-section and yet provides for a more even torque with the fastener.

                            al
                            I spent most of my money on women and booze, the rest I just wasted.

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                            • #15
                              Jerry Kieffer makes taps that are 300 tpi and finer, IIRC. He wrote an article for HSM back in 2006 or thereabouts on using optics for micro machining and has a pic of some of his "fine" work. He also has had other articles in magazines such as Model Engine Builder on this sort of work. Most of his small work is done on Sherline equipment; he told me that my HF 7X10 isn't worth a darn for that sort of thing because the headstock bearings simply aren't good enough.

                              Jerry also did a seminar at one of the N.A.M.E.S. conferences on the making of very small, fine thread taps. Hardening them is kinda tricky. :-)

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