Threadmilling NPT depth issue

[Tim Johnson]

When I find my depth for npt threads I add the handtight engagement (L1 in the "Good Book") and the wrench makeup length (L3). Is this the correct depth for threadmilling? I'm being told that my threads are too shallow. How do you find the correct depth?

[Joels]

When i threadmill NPT threads i use all the threads on the tool. For example our 1/4-18 NPT threadmill has 11 teeth and is .500 long so i go in the part .5 and make the threads. I use all the teeth on the threadmill as the depth.

[?Mark]

Hi Tim,

I also tended to go too shallow while thread milling.

Your numbers look right, but to simplify I just use L2 (L2 almost =L1+L3) from the same "Good Book"

 

Mark

[Tim Johnson]

Joel,

I looked in three different thread milling catalogs and got three different lengths.(1/8 NPT) I would like to create a standard depth.

 

Mark,

I used the L1+L3 because the threads are internal. I would have used L2 for external threads but now I'm not so sure. I tried to get our production foreman to check the purchased mating parts with a ring gage, but he doesn't want to do it.

[Kevin Goddard]

How about L1+L3+V ? Just a thought. Let us know if you find a difinitive answer.

[Jaz]

I always try to cut 3-5 more threads past the L1+L2 length, as if emulating what a tap would cut. Then engagement can be adjusted with just a little cutter comp and/or offset change.

[medaq]

I use a pipe tap gage to check my depth. Screw it in and see where the flat stops. It the flat is not flush then I know what to do...

 

Jim

[Eric S.]

We also use a gage to check the tap depth. But I believe it usually works out to 3-4 turns of engagement.