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Turning inch theads vs. metric threads?

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  • Turning inch theads vs. metric threads?

    I have never turn inch threads on my lathe. I live in a civilized country not a third world country. When I cut metric threads the lead nuts don't get disengaged at the end of the threading pass. The spindle gets reversed to go back to the start of the threading pass. To me this seems a much more efficient way to cut threads if you have an easily reversed spindle with a brake. I do. This might seem a dumb question but is it possible to cut inch threads the same way? I don't have a threading dial on my lathe but it does have inch threads on the gear box. The possibility does exist for me to buy inch nuts and try it just in case in the future I have to cut primitive threads for backwards countries!
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  • #2
    Yeah. If your leadscrew is metric that's the way you'll have to do it.
    21" Royersford Excelsior CamelBack Drillpress Restoration
    1943 Sidney 16x54 Lathe Restoration

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    • #3
      Yep, it works exactly the same way, back the tool out of the cut and run the spindle in reverse back to the starting point.I used to do that all the time when I first got my lathe as I did not have a threading dial at the time.

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      • #4
        I have a lathe with an inch lead screw but I thread the metric way for both types of thread. It's better to just do it one way I think, easier to get it into muscle memory.

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        • #5
          What leadscrew do you have? Imperial or metric?
          I have imperial leadscrew, and metric transpose gears, and a thread dial, when cutting metric I must keep half nut on the same location on the leadscrew (reverse the lathe)
          Cutting imperial threads I can open half nut and pick up same location via thread dial

          I thought that if you have a metric lathe, with thread dial, you can open the halfnut, correct?
          And cutting imperial on same lathe you keep halfnut closed as above?

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          • #6
            Metric lead screw and metric thread, if the pitch of the thread devides a whole number with the lead screw pitch, you can open the half nut anywhere without a thread dial.
            Helder Ferreira
            Setubal, Portugal

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            • #7
              Just remember that the worlds first thread standards were Whitworth in the UK. Of course, we are fully metricated now, unlike the former colonies who produced their own version of imperial threads purely for political purposes.

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              • #8
                half nuts closed works for both thread types. however if the thread is long i disengage anyway and match the position by eye, at least on the first passes.

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                • #9
                  Depends entirely on the machine, this morning (before the power went off here in NJ) I was single pointing M32-2.5 left handed threads 50 mm long in inch mode.

                  The lead is .09842"
                  Start diameter 1.259"
                  End diameter 1.259"
                  Depth of thread .063" to start, if they don't measure adjust as needed then run again, start low.
                  Start Z -1.968" on this machine all dimensions past Z0 towards the spindle are negative
                  End Z .200"
                  If threading a small diameter part when using a live center keep the withdraw clearance very low to keep from hitting the center with the tool, this nearly always ends in tears, do not ask how I know this (-:

                  Below is a 1 1/4"- 4TPI RH acme thread in a canned threading cycle.
                  To cut a different thread just change the relevant numbers and tool and have at it, it is very simple, no 1/2 nuts used.
                  This lathe and control was made in 1996 so it is not modern, no touchscreen just a limited keypad. The last time that I threaded on a manual lathe was 7 or 8 years ago, I do not miss it at all.


                  Last edited by Bented; 08-04-2020, 02:43 PM.

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                  • #10
                    BF sounds like you have a standard leadscrew check pitch..
                    if it is say 4 tpi, then you can cut 4, 8, 12 , 16, 20, 24 etc without a thread guage. And you can disengage tote 1/2 nuts

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                    • #11
                      You need to get out of the forest and into the modern world- you know, Whitworth, B+S, etc
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                      • #12
                        interesting having a gear box on both my lathes the Colchester has metric / imperial the Myford is mainly lmperial and this old goat is kinda locked into imperial my question is how do you determine if the leed screw is imperial or metric

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                        • #13
                          Originally posted by Kiwi View Post
                          interesting having a gear box on both my lathes the Colchester has metric / imperial the Myford is mainly lmperial and this old goat is kinda locked into imperial my question is how do you determine if the leed screw is imperial or metric
                          Stick a scale next to it. Count how many threads per inch. Typically 8 or 16 on smaller lathes 4 on midsized lathes, and 2 and 1 on large lathes. Doesn't match up to a whole number? Most likely metric.
                          21" Royersford Excelsior CamelBack Drillpress Restoration
                          1943 Sidney 16x54 Lathe Restoration

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                          • #14
                            Keeping the half nut engaged on the lead screw and reversing the rotation will work for just about any kind of thread: English, metric, non-standard, whatever. If you can set up the lathe to cut the thread, that will work.

                            The thread dials are for speeding up the work by providing a faster way to get back to start for the next pass.
                            Paul A.
                            SE Texas

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

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                            • #15
                              Black Forest: Monarch lathe company answered that question years ago. The series 600's and I think others had that feature built in. They have a handle just to the right of the carriage on the top rod that will reverse the lead screw without stopping the spindle. When doing so, the carriage travels back to where you want it. When you thus get back to your starting point, you position the handle in the center position. The carriage stops, then crank in the cross slide to start another cut, feed the compound in or stop for any purpose. When ready to take another cut, just lower the handle and it will pick up the lead and take another cut. It also has a stop clamp on that top rod that will raise the lever up and stop the travel of the carriage at the desired position. It is much simpler than it sounds.Hope this all makes sense.
                              JH
                              Last edited by sarge41; 08-04-2020, 05:52 PM.

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