how to calculate beginning point when programming pipe threads on a lathe

# Thread: how to calculate beginning point when programming pipe threads on a lathe

1. ## how to calculate beginning point when programming pipe threads on a lathe

Joe

2. see how this works for an internal thread.

L1 and K0 come from any good NPT dimension chart

thread height = (pitch value * .8)

minor diameter at the face = (L1 * .0625) + K0

major diameter at the face = minor + (2 * thread height)

Software For Metalworking
http://mrainey.freeservers.com

3. Tag for when I need to use this!

Thanks M.

4. ## pipe threads

mrainey,

Wow! Very nice program. I don't have my paypal info with me right now but when I get back to my desk I will definitely purchase this info. Very nice. What a time saver! By the way, I went back to the Machinery Handbook and figured out the calculations and I now have a working formula for NPT's whether it's a full thread or some part of a full thread (I don't know about you guys but it seems like I am always being asked to make shortened pipe threads for unique applications). Nevertheless, I love the amount of information that your program puts at one's fingertips. Thanks again.

Joe

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Originally Posted by mrainey
see how this works for an internal thread.

thread height = (pitch value * .8)

minor diameter at the face = (L1 * .0625) + K0

major diameter at the face = minor + (2 * thread height)
This is great information.

I have another question about lengths. To make standard internal NPT thread (eg. 3/8 NPT), what is the formula to calculate how long the thread should be?

I never know how far to machine the ID and how far to machine the thread.
I usually machine a length equal to L1+L3. Is that remotely correct?

Thanks.

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