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Metric Threading with an Inch Lead Screw

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  • Metric Threading with an Inch Lead Screw

    A while back, I started a thread called: "Baffled by metric threads" http://bbs.homeshopmachinist.net/thr...metric-threads wherein I admitted my lack of knowledge of the subject, and the need for enlightenment. For the most part, the result was a 22 page can of worms. A few responders offered good advice, and a few not so much. Mostly it became a pissing contest over the use of metric vs. imperial measurement. In the end, I learned much about metrics, my new to me lathe, and to be careful of what I post on this forum. I also learned that as with most anything, there are more ways than one to skin a cat.
    If you have an interest in an easier method of single pointing threads, check out this You Tube video by Tom Lipton of OX Tools: https://www.youtube.com/watch?v=HXt4TWa382Q
    I watched it a couple of times, then following Tom's instructions, cut a perfect M40 x 1.5 thread on the first attempt.
    Last edited by Dave C; 08-21-2015, 03:57 PM.
    “I know lots of people who are educated far beyond their intelligence”

    Lewis Grizzard

  • #2
    I saw that video some time ago and it tickled my memory without triggering anything definite. This time I remembered: old Earl Richardson on one of the 24" Axelsons on the west bay aisle cutting all those diametral pitch worms for the Tartar missile elevators. He used the same trick demonstrated by Tom Lipton and I remember Earl telling me someday this method of keeping the index in time by watching the thread dial when the half-nut's open would come in handy so don't forget it.

    Well I did forget it and sorry, Earl, your lesson failed to stick. All these many years I've been telling horror stories of never opening the half-nut on irrational pitches. Dave, I failed to pass on Earl Richardson's trick back in my earlier posts and I apologize.

    But otherwise in all other stuff I'm infallible. Honest - this time.

    Tom, great video. Cutting Metric threads and other oddball leads from Imperial lead screws is always a nail biter. You memorably presented a real jewel of a threading trick.
    Last edited by Forrest Addy; 08-21-2015, 05:10 PM.

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    • #3
      I watched the video and left this comment:

      This is a good "trick". Thanks. I have not done much threading, just a 3/4"-8 LH SQ thread on some chuck screws, and some 1/4"-20 threads where I turned the tool upside down and used reverse. I kept the half-nut engaged for the 8 TPI because it was too hard to hit the dial tick with a 16 TPI leadscrew and a little 64 tooth thread dial on my little HF 9x20.
      I have not chased any metric threads, but this looks like a good way to do it. It may not work as well for LH threads or for cutting in reverse with an upside-down tool, however. For that you would leave the half-nut engaged as you traverse the carriage and tool to the relief at the shoulder, possibly turning the spindle by hand or with a variable speed drive that will stop soon enough, then advance the compound and cross-slide for the next cut, and turn it on in reverse for cutting.
      http://pauleschoen.com/pix/PM08_P76_P54.png
      Paul , P S Technology, Inc. and MrTibbs
      USA Maryland 21030

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      • #4
        Now THAT is a very handy trick. I've been threading for simply ages (not very many metric ones) and that has never occurred to me. Next time I need metric I'll give it a try.
        Thanks.
        ...lew...

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        • #5
          That is a neat trick. Of course, it probably is a little more difficult for coarse pitches or if your lathe doesn't stop very quickly.

          That guy does like to talk though! 15 minute video for a 30 second explanation.

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          • #6
            Excellent, thanks for that!

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            • #7
              Ok Im lost, the video looks great but does not state what the gear box setting is. I have SB13 with quick change gear box, how do I set the feed rate to cut metric threads?

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              • #8
                Originally posted by quadrod View Post
                Ok Im lost, the video looks great but does not state what the gear box setting is. I have SB13 with quick change gear box, how do I set the feed rate to cut metric threads?
                You'll have to look at the SB documents to find out how to set up your lathe. It will no doubt be different than the one in the video. He wasn't focusing on the setup for metric threads so much as addressing the special issue of not releasing the half nuts when you've set up gearing for a non-standard ratio.
                .
                "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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                • #9
                  Originally posted by quadrod View Post
                  Ok Im lost, the video looks great but does not state what the gear box setting is. I have SB13 with quick change gear box, how do I set the feed rate to cut metric threads?
                  I offer the following with no intention of insulting your intelligence. It seems that perhaps there is something you don't understand about metric threading.

                  Aside from setting the gear ratios so the lead screw turns at a rate proportional to the spindle to produce a particular metric thread pitch there is the issue of the threading dial not properly telling you when to engage the half nuts. The threading dial only works for Imperial threads and British Standard threads or any odd thread that is measured in threads per INCH.
                  Therefore other methods must be adopted in order to be able to release the half nuts, or you must leave them engaged at all times and reverse the spindle allowing the carriage to retrace it's path at exactly the same rate, and position, on the lead screw as it moved while cutting the thread. This makes it difficult to thread to a shoulder or particular stopping point. Failure to do so will result in a mismatch that destroys the job. The video explains an excellent alternative to leaving the half nuts engaged ALL THE TIME while allowing them to re-enter the lead screw in the exact same position it was originally in when cutting began.
                  There is another method that requires a carriage stop and some other visual aids, all of which I cannot remember at the moment. In my few past experiences of metric threading I've used the reverse spindle method, stopped early and hand rotated to the shoulder, a slow pain. The method shown is simple, easy to remember, allows threading to a shoulder at speed and no additional equipment is necessary. In reality it's using the reverse the spindle method along with the thread dial to position the carriage and lead screw in the exact same position as the operation began.
                  I hope this helps your understanding.

                  Comment


                  • #10
                    I understood the video just fine. It just means I still need metric transposing gear set.

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                    • #11
                      Excellent tip. Thanks for posting it.

                      And yes, you do still need metric transposing gears. No way out of that.
                      Paul A.
                      SE Texas

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

                      Comment


                      • #12
                        Originally posted by quadrod View Post
                        I understood the video just fine. It just means I still need metric transposing gear set.
                        Apparently I misunderstood your first post. Apologies.

                        Comment


                        • #13
                          There is a link at the end of the video that explains the metric threading process in detail. It is rather long, but covers everything you ever needed to know about cutting threads on a lathe. If you are new to metric threading as I am, and just want a text version of what you saw in Tom's video, Go here: http://conradhoffman.com/metricthreading.htm and scroll down to: "You Have to Keep the Half Nuts Engaged for Metric Threading" - Not! If you are open to learning the mechanics of threading on a lathe, read the whole thing. IMHO It's a good read and will be worth your time.
                          “I know lots of people who are educated far beyond their intelligence”

                          Lewis Grizzard

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                          • #14
                            Hi Dave C,

                            I was going to post this in your previous thread, but as you say, it got a little OT.

                            Anyhow this is something that I have posted about before. This little gem can take some of the pain out of doing metric threads with an inch leadscrew.

                            This previous thread covers a lot of the bases.

                            http://bbs.homeshopmachinist.net/thr...t+becksmachine

                            Dave

                            Comment


                            • #15
                              Originally posted by firbikrhd1 View Post
                              I offer the following with no intention of insulting your intelligence. It seems that perhaps there is something you don't understand about metric threading.

                              Aside from setting the gear ratios so the lead screw turns at a rate proportional to the spindle to produce a particular metric thread pitch there is the issue of the threading dial not properly telling you when to engage the half nuts. The threading dial only works for Imperial threads and British Standard threads or any odd thread that is measured in threads per INCH.
                              Therefore other methods must be adopted in order to be able to release the half nuts, or you must leave them engaged at all times and reverse the spindle allowing the carriage to retrace it's path at exactly the same rate, and position, on the lead screw as it moved while cutting the thread. This makes it difficult to thread to a shoulder or particular stopping point. Failure to do so will result in a mismatch that destroys the job. The video explains an excellent alternative to leaving the half nuts engaged ALL THE TIME while allowing them to re-enter the lead screw in the exact same position it was originally in when cutting began.
                              There is another method that requires a carriage stop and some other visual aids, all of which I cannot remember at the moment. In my few past experiences of metric threading I've used the reverse spindle method, stopped early and hand rotated to the shoulder, a slow pain. The method shown is simple, easy to remember, allows threading to a shoulder at speed and no additional equipment is necessary. In reality it's using the reverse the spindle method along with the thread dial to position the carriage and lead screw in the exact same position as the operation began.
                              I hope this helps your understanding.
                              +1.
                              I don't mind leaving the half-nuts engaged for metric threads, but as above, it is a pain coming up to a shoulder without being able to stop suddenly without a brake, and this method is great because of exactly that.

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