Lathe Threading - 2 threads in sync

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17 Dec 2019 08:34 #152782 by davidimurray
Hi All

I've got some parts to make that are a stay bar, necked in the middle with threads on either end. The threads on either end need to be in sync with each other (the corresponding thread is cut with a special long tap). The question is do I need to cut the thread from one end all the way through the bar (20" long) or can I cut just the 6" at either end with a thread on and keep the two threads in sync?

Cheers

Dave

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17 Dec 2019 10:50 - 17 Dec 2019 10:56 #152786 by Leon82
I would cut it in one shot with a center. What's the diameter?

On a fanuc controlled lathe as long as you don't unclamp the Chuck it will help the sync. If Linux CNC is the same you could rgh and finish the first half. Then add a steady rest and finish the second half of it tends to chatter
Last edit: 17 Dec 2019 10:56 by Leon82.

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17 Dec 2019 11:35 #152787 by Hakan
I would guess that can be done. If the starting Z-point is an even number of thread pitches away it might possibly, on a good day, perhaps sync.

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17 Dec 2019 11:48 #152788 by davidimurray
My plan was to machine between centres, rough the thread parallel section, then neck the centre section, followed by threading the complete length (obviously nothing cut on the centre section as it has been necked). Easy enough to do, but obviously over half the thread cutting time will be in fresh air. Hence the query if it was possible to sync two threads in someway.

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27 Dec 2019 02:55 #153253 by jmelson
If the two threading operations are started at a Z value that is an integer multiple of the thread pitch, then they will be in sync, to the accuracy of the lathe's leadscrews and encoders. So, for instance, if the thread was a 12 TPI pitch, and one starts at Z=0 and the other starts at Z=4.0, then they would be exactly in sync, as 4 is an integer multiple of 0.083333 (which is the pitch, 1/12)

Jon

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