NTP

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15 Dec 2012 01:13 #27734 by BigJohnT
Replied by BigJohnT on topic NTP

Here are some G code files to cut NPT tapered pipe threads


There is a "gotcha" with tapered threads and G33. G33 moves at the desired pitch along the path, not along the Z axis.
This may not be noticable for a shallow angle, but does need correcting for.

(This may look like a drawback, and some people consider it a bug, I am of the opinion that it allows for more flexibility, creating scroll chucks for example.)


For NTP threads IIRC the difference between actual pitch and proper pitch is so small that most machines are not accurate enough to make any difference on the thread. But good to point that feature out.

John

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18 Dec 2012 10:44 - 18 Dec 2012 10:46 #27819 by joekline9
Replied by joekline9 on topic NTP
Using G33 For pipe threads:

Andy is correct and I agree that G33 works like it should.

Pipe threads have 3/4" taper per foot (.375 per side)
For 1.000 travel along the Z axis you must move 1.000488 along the tapered drive line.

When you calc the pitch instead of [ 1.0 / TPI ] just do [ 1.000488 / TPI ]

Example:
For 3/4" NPT
K = [ 1.000488 / 14]
Last edit: 18 Dec 2012 10:46 by joekline9. Reason: include comment about Andy's post

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28 Jan 2013 07:44 - 29 Jan 2013 21:42 #29209 by joekline9
Replied by joekline9 on topic NTP
I reworked the G33 pipe threading routine to use named parameters.
Also made it do progresive in feed from First_Cut to Min_Cut.
The infeed angle is automatically derived from #<_X_Depth> and #<_Z_Depth>
making the routine very flexible.
I use seperate ngc files for each thread.
The individual thread sizes all use the same sub file called "thread-loop.ngc".
It must be in the path as in .ini file [DISPLAY] PROGRAM_PREFIX = ...

I wish we could use G76 for tapered threads. I tried to find the source files but could not.
They don't seem to be where other canned cycle code is. Can anyone point me to them?

Thanks Joe K
Attachments:
Last edit: 29 Jan 2013 21:42 by joekline9. Reason: typos

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29 Jan 2013 05:25 #29239 by andypugh
Replied by andypugh on topic NTP

I wish we could use G76 for tapered threads. I tried to find the source files but could not.
They don't seem to be where other canned cycle code is. Can anyone point me to them?


Have a look in src/emc/rs274ngc/interp_convert.cc around line 4120

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