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Turning inch theads vs. metric threads?

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  • #16
    It was common on a lot of lathes, including Hendeys, Pacemakers, and Sidneys like the one I'm repairing.
    21" Royersford Excelsior CamelBack Drillpress Restoration
    1943 Sidney 16x54 Lathe Restoration

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    • #17
      Once I got the Hardinge HLV rebuilt, I haven't gone back to cutting threads on the myford with its threading dial.

      Having a once per spindle rev synchronised single tooth dog clutch to select forward or reverse feed and end stops that disengage it mean that you can use the gearbox for the threads it does or changewheels for any others, keep the half-nuts engaged, keep the spindle turning in the same direction. Then:- forward feed; retract the tool; reverse the feed; put more cut on and un-retract the tool; forward feed. Lather, rinse and repeat.

      With the quick retract topslide, the action is so rapid that you can be down to about three seconds per cutting cycle on a 10mm long M6 thread at 1000rpm. It's not as fast as using a die box, but it's orders of magnitude faster than I could ever achieve on the Myford.
      Last edited by Mark Rand; 08-04-2020, 06:38 PM.
      Location- Rugby, Warwickshire. UK

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      • #18
        Originally posted by Black Forest View Post
        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!
        The short answer is yes.

        The principle is exactly the same whatever the thread. Just cut, withdraw, stop, reverse, stop, advance, rinse and repeat. The lathe will happily cut whatever pitch you've set the gearbox to. The pitch of the leadscrew is irrelevant.

        My lathe came fitted with both a reversing switch and a completely redundant thread gauge, which latter I immediately removed and have never used. The only utility it would provide is to speed up the wind-back-to-start, and as I run the lathe from a VFD, it's easy to speed the motor up for that phase of the operation if it's a long thread and I'm in an unaccustomed hurry. I do have a vague memory of once doing that.

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        • #19
          I made a stud today with metric on one end and imperial on the other. I of course had to reverse the lathe to do the metric thread. I will say that I much, much prefer using the threading dial and am much faster that way. Especially on a 10 TPI where I can bang it in on any line.
          21" Royersford Excelsior CamelBack Drillpress Restoration
          1943 Sidney 16x54 Lathe Restoration

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          • #20
            A lot of lathes with a metric leadscrew need transposing gears changed from spindle to gearbox to cut an imperial screw.
            There should be tags or plates describing this on the lathe, you need to check this out.
            Ditto an imperial machine with imperial gearbox and leadscrew generally needs 1 or 2 transposing gears changed to cut a metric thread.

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            • #21
              Originally posted by dian View Post
              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.
              I've seen non-native threads cut while disengaging the half-nuts and winding back by having a dead stop on the bed to bring the carriage back to and re-engaging on the same thread-dial line, not completely convinced so I'll have to give it a try sometime If I want to be really testing, I could swap a 45 to a 43 on the spindle to avoid matching *any* known thread...

              Dave H. (the other one)
              Rules are for the obedience of fools, and the guidance of wise men.

              Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

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              • #22
                Originally posted by Paul Alciatore View Post
                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.
                I'm with Paul on this one. Sure you can keep the half nuts engaged. But most Imperial threading is done way faster using the thread dial. And produces less wear on the half-nuts and lead-screw. Also threading up to a shoulder is another consideration. Do that more often than you'd think.

                Best Regards,
                Bob
                Last edited by rjs44032; 08-05-2020, 12:44 PM.

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                • #23
                  When single-pointing metric threads on a lathe with an Inferial leadscrew the inherited wisdom is to never disengage the half-nuts. However, this makes threading to a shoulder or a runout groove difficult at best. Thankfully, there is a technique that allows one to disengage the half nuts without losing registration on the thread. It involves the use of the threading dial but not in conventional manner.

                  1. After setup (including checking the pitch) start the first pass by engaging the half-nuts on a selected number on the threading dial. (Here we'll assume you engage on '1'.)

                  2. When you reach the runout groove/shoulder disengage the half-nuts and turn off the lathe motor. Back the tool out but do not move the carriage. You will note that the thread dial no longer points to '1' because the motor inertia continued to turn the lead screw after you turned the motor off.

                  3. Start the lathe motor in the reverse direction. The '1' on the thread dial will begin to move back towards the index mark. When it reaches the index reengage the half-nuts. You're now back in sync with your thread.

                  4. Let the leadscrew drive the carriage to the right until the tool clears the workpiece. Stop the lathe. Put on the next cut increment and start the lathe in the forward direction to make the next cut on the thread.

                  Regards, Marv

                  Home Shop Freeware - Tools for People Who Build Things
                  http://www.myvirtualnetwork.com/mklotz

                  Location: LA, CA, USA

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                  • #24
                    I think I'll just leave this here, so that people can educate themselves:
                    http://www.metrum.org/measures/index.htm

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                    • #25
                      Threading to shoulder leaving haunts closed is not so bad with a good brake, did it a lot,

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                      • #26
                        Originally posted by mklotz View Post
                        When single-pointing metric threads on a lathe with an Inferial leadscrew the inherited wisdom is to never disengage the half-nuts. However, this makes threading to a shoulder or a runout groove difficult at best. Thankfully, there is a technique that allows one to disengage the half nuts without losing registration on the thread. It involves the use of the threading dial but not in conventional manner.

                        1. After setup (including checking the pitch) start the first pass by engaging the half-nuts on a selected number on the threading dial. (Here we'll assume you engage on '1'.)

                        2. When you reach the runout groove/shoulder disengage the half-nuts and turn off the lathe motor. Back the tool out but do not move the carriage. You will note that the thread dial no longer points to '1' because the motor inertia continued to turn the lead screw after you turned the motor off.

                        3. Start the lathe motor in the reverse direction. The '1' on the thread dial will begin to move back towards the index mark. When it reaches the index reengage the half-nuts. You're now back in sync with your thread.

                        4. Let the leadscrew drive the carriage to the right until the tool clears the workpiece. Stop the lathe. Put on the next cut increment and start the lathe in the forward direction to make the next cut on the thread.
                        Yep, that's what I do when metric threading to a shoulder.
                        21" Royersford Excelsior CamelBack Drillpress Restoration
                        1943 Sidney 16x54 Lathe Restoration

                        Comment


                        • #27
                          Originally posted by Bented View Post
                          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.


                          what kind of insert did you use and do you know the resulting pitch diameter?

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                          • #28
                            Kennametal topnotch 4 TPI acme insert, the threads were measured over wires. Due to the large lead I used a gauge block across the wires. The PD measurement over wires is 1.342" + .100" for the gauge block.

                            For the 32 mm thread used a 2.5 mm lead Iscar laydown insert, the threads were also measured over wires and took 3 adjustments to sneak up on the PD.
                            Last edited by Bented; 08-06-2020, 06:06 AM.

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                            • #29
                              With a manual lathe, all you need is a change gear set with a 100:127 ratio. What the leadscrew is (inferial or metric) does not matter a hoot as long as you have that change gear.
                              Threading dials are nice - sometimes. Otherwise just disconnect and wind back, then realign by eye. Metric or imferial: it does not matter.

                              Me, I just tell the CNC what I want and it goes and does it.

                              Cheers
                              Roger

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                              • #30
                                When I single point I do it this way. I have a retracting threading tool holder. It originally came with a HSS tool for threading. I made a holder for carbide inserts. Do you think it would be faster using a thread dial than what I am doing in the video? I as you can see use a lever to retract the insert tool out of the thread when I reach the run off grove. My lathe does have a brake so it goes pretty fast threading with the half-nut engaged.
                                https://www.youtube.com/watch?v=fxOqH9izVh4

                                When I use a die I built a die holder that goes in the tailstock.
                                https://www.youtube.com/watch?v=ZcH3pdsrBmc
                                Location: The Black Forest in Germany

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

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