Chasing threads/Rethreading.

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10 Jan 2023 10:27 #261431 by jimwhiting
Hi,

How does one go about chasing out an existing thread using CNC Lathe, or rethreading? I used to do it manually by lining up the thread whilst locking the lathe on the lead screw. Then chase it out or rethread it to its metric/imperial alternative.
Or am I going to need a set of dies/taps to do this now?
Thanks,

Jim.

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10 Jan 2023 11:08 #261434 by jimwhiting
And after some more reading I managed to find the answer.

Spindle Synchronised Motion but with the speed set to 0.

I tried one of the g76 wrappers with the speed set to 0 and it works so I can setup the job... Easy for external threads, not so much for internal.

-Jim.
The following user(s) said Thank You: tommylight

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10 Jan 2023 13:18 #261442 by andypugh
You can tweak the start of the threading pass to get the phase correct, or rotate the work in the chuck. (or move the tool in the holder, sometimes)

I guess you already saw:


Start the cycle, turn spindle override to zero, rotate the work in the chuck to align the thread to the tool, then turn the spindle back on.

If, for some reason, this is difficult then tweak the start point:
Starting the threading cycle at a clearance diameter, stopping the machine mid-cycle, noting the Z, then jogging into engagement and noting Z again should allow you to work out how far the start point needs to be moved.

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10 Jan 2023 13:59 #261445 by jimwhiting
Yes, very helpful that video. (and your lathe gui, and a whole bunch of other stuff). Thank you!

I have made a boring bar style holder for the internal threading tool that allows me to loosen some grub screws and have it slide in the Z axis so I can also use that to adjust.

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