1. ## Pipe thread

I need to do a pipe thread 1" NPT 11 1/2.
My G-Code are:
T0202
G0 X1.281 Z.06
S400 M3
G76 P010000 Q00 R00
G76X1.1304 Z-.99 P753 Q150 R-.031 F.08695
G0 X5 Z 7 M30

What's wrong?
Q=150 it is for 25 pass.

Best regards.

2. What is wrong? Is 25 passes too many? What problem are you having?

3. Q in the first block is minimum depth of cut.
Q in the second block is first depth of cut (not directly related to number of passes).
Depth of cut gradually reduces from first depth of cut to minimum depth of cut, automatically.
Replace Q00 in the first block by, say, Q15, in case this is creating the problem.

4. ## Pipe thread too loose

Hello dcoupar

My problem is my thread are too loos. Went I have cut my threads, I have stopped my CNC after ten pass and the result have been very loose.

I sure that my R and my X values are wrong but I don't know what are the good values. What the way to find the good values?

Best regards
A++ J-D

• Yes, your numbers are incorrect. Try this.

G00 X1.4889 Z0.2609
G76 P010260 Q20 R0
G76 X1.1911 Z-0.6828 R0.0295 P652 Q098 F0.0870

• But he wants threads up to Z-.99

• He also wanted to thread to 1.1304 diameter, which is too small. What's your point?

• ## Hello dcoupar

I have un other question for you.

How did you find the value of P652 and the Q098 and the last one R = x axis incremental taper.

Best regards.

A++ J-D.

• According to the Machinery's Handbook 25th Edition, the minimum height of pipe thread is 0.06261 and the maximum is0.06957. I put it near the mean.

The Q098 is approximately 15% of the .0652 height. It's just a starting point. If it's making too many passes, increase Q a little.

R is 0.03125 * the total Z movement (.2609+.6828).

I started Z 3 threads off the face. This should give Z-axis plenty of time to get "up to speed". Also it would allow you to offset Z - should you want the thread to be a little longer. The effective thread length for a 1" - 11-1/2 is .6828, so you shouldn't need to go too much.

• ## Thanks a lot for your help.

dcoupar

You are the best

Best regards

A++ J-D

• Glad I could help.

• R should probably be negative in this case???
I have never made pipe threads, so I am not sure.
Pl correct me if I am wrong.

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