Cutting a tapered thread with G76

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09 Oct 2018 23:36 #118608 by JR1050
I am baffled with how the tapered thread command of lcnc works. I have a 16mm Id thread, the last half of the thread is in a collet that is clamped causing the thread to be deformed and tapered , smaller on the back end. I'd like to program the taper out, which on fanuc lathes was a an I value, which was the dia distance between the minors at either end of the taper.
I need to program about .003 on the dia over and inch.
My present command
G76 P.059K.075I-.01Q0 H3
How is this done?

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10 Oct 2018 13:32 #118638 by andypugh
You can't (currently) do a constant-taper thread with G76.

But it sounds like you only need an exit taper?

linuxcnc.org/docs/2.7/html/gcode/g-code.html#gcode:g76

E and L control the taper, but only the distance over which it occurs. It is always a taper from full depth of thread to zero depth of thread.

If you want a straight taper then you can use G33 and programme each pass separately.

Or there is this experimental work (and discussion)
sourceforge.net/p/emc/mailman/emc-develo...any.com/#msg35333774

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03 Oct 2019 13:56 #146978 by CNCCustoms
Hi

Has this been resolved? Can Linuxcnc do tapered threads with G76 now?

Thanks,

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03 Oct 2019 16:06 #146991 by andypugh
I don't think anything further has happened You could try joining the conversation on the mailing list. The multispindle letter clash has been resolved now.

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12 Aug 2020 15:43 #178041 by RotarySMP
Bump...

Can LinuxCNC still not tapered threads?
Mark

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12 Aug 2020 17:19 #178047 by andypugh
You can do it with G33

I don’t know what happened to the tapered G76 work.
The following user(s) said Thank You: RotarySMP

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12 Aug 2020 17:27 #178048 by RotarySMP
Thanks for the quick response Andy,

Bummer. Now I have to write a subroutine to do it with G33, and you have seen how careless my code is :) I will take me an hour to write it and two to debug. Good practice.
Mark

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28 Jan 2021 01:25 #196872 by mooser
Just wondering if this was ever resolved as I need to cut a 1/8-pipe thread on some parts? (tried a 2 line G76 but it complained about missing move axis)

Thanks
M

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28 Jan 2021 01:41 #196874 by tommylight

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28 Jan 2021 02:35 #196879 by mooser
I don't think I've ever used a G33 in my life...
I need to make a 1/8-27 npt go up and then become a 5/16- 24 straight so maybe it's time to learn
M

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