1/4 npt internal thread - CNCzone.com-The Largest Machinist Community on the net!

richcash · #1 10-20-2011, 01:40 PM

Hi, I have a 1/2 npt and 1/4 npt internal threads I have to machine (screw cut) on a fanuc lathe, can't tap as in very hard steel. I have a 08 14 NPT insert and 06 18 NPT for the 1/4 thread. Problem is I know it's a 1/16 taper but don't know the start dia or the thread length or what size to bore the taper. Do have a engineers hand book that's only any good for the tapping drill size for both these threads, any help would be great.

richcash · #2 10-20-2011, 01:53 PM

Also I have step gauges and program in metric using a G76 for the thread

txcncman · #3 10-20-2011, 02:01 PM

Is this what you are looking for?

richcash · #4 10-20-2011, 02:12 PM

Have seen this chart yes Thanks

txcncman · #5 10-20-2011, 02:19 PM

Is the problem in that you do not know how to read the information off of the charts?

richcash · #6 10-20-2011, 02:34 PM

Yep found it hard to make sence of the chart, I have the job on the machine and need to crack on in the morning. Was just looking for a quick easy way out to get the figures and complete the job

txcncman · #7 10-20-2011, 05:34 PM

For 1/4-18 - Starting Diameter is 0.49163.

For 1/2-14 - Starting Diameter is 0.77843.

Does that help?

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