2 threads past or flush?
#1
04-07-09, 11:19 PM
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2 threads past or flush?
Did a search, couldn't find a definitive answer.
Schedule 40 black iron (steel) pipe when threading NPT, do you go two threads beyond the die end or stop when it's flush?
I've seen/read material that gives conflicting advise.
What's the correct way?
Thank you.
Schedule 40 black iron (steel) pipe when threading NPT, do you go two threads beyond the die end or stop when it's flush?
I've seen/read material that gives conflicting advise.
What's the correct way?
Thank you.
#2
04-08-09, 10:58 AM
Originally Posted by BooDaa
Schedule 40 black iron (steel) pipe when threading NPT, do you go two threads beyond the die end or stop when it's flush?
Pipe threads are (or should be) tapered. Proper tightness is determined by torque, not by how much they are engaged. There are guidelines for the torque, but it depends upon the size of the pipe. Most people just go by "feel."
If your male threads are completely engaged in the female fitting, then I think there is something wrong with the threads.
Doug
#4
04-08-09, 07:43 PM
Originally Posted by sidny
I think the writer meant how far to cut the threads, most plumbers go one or two threads past the end.
Doug
#5
04-09-09, 06:27 PM
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Yes, a couple threads longer than the die or stop when the die is flush with the pipe end? Anyone have the skinny on this and the what and what for of threading beyond for a couple threads?
Sorry for not being clear.
Thanks.
Sorry for not being clear.
Thanks.
#6
04-09-09, 07:47 PM
I'm thinking that the "Plumbing & Piping" forum might be another place to post your question.
Modern hydronic heating systems don't use threaded pipe nearly as much as in days of yore. Soldered copper pipe has pretty much taken over - except for natural gas piping.
Doug
Modern hydronic heating systems don't use threaded pipe nearly as much as in days of yore. Soldered copper pipe has pretty much taken over - except for natural gas piping.
Doug
#8
04-09-09, 08:32 PM
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Thanks NJ Trooper and gilmorrie.
I guess I'll count the teeth in my dies.
Here's an example of threading until flush:
YouTube - Steamfitting/Pipefitting #2
Still leaves me wondering the purpose of going 2 threads by.
I like old school and simple, BI does that for me. I just don't have access to much in the way of nipples etc 1-1/4 but have lots of pipe and a ratchet threader. Have threaded pipe before but only to screw into flanges/bases etc and have never needed to worry about water tightness.
Thanks very much.
I guess I'll count the teeth in my dies.
Here's an example of threading until flush:
YouTube - Steamfitting/Pipefitting #2
Still leaves me wondering the purpose of going 2 threads by.
I like old school and simple, BI does that for me. I just don't have access to much in the way of nipples etc 1-1/4 but have lots of pipe and a ratchet threader. Have threaded pipe before but only to screw into flanges/bases etc and have never needed to worry about water tightness.
Thanks very much.
#9
04-09-09, 08:57 PM
Boo, I found this e-book that looks like a pretty good read if yer new at doing BI... I just read the first page and it's pretty straightforward writing... the book is published in 1918, some of the illustrations are cool... check out the one of the water heater a few pages after the pipe threading part.
Chapter-XII-Pipe-Threading
Looks like a neat site, gonna pokaround there and see what else they got.
Chapter-XII-Pipe-Threading
Looks like a neat site, gonna pokaround there and see what else they got.
Last edited by NJT; 04-09-09 at 09:18 PM.
#11
04-10-09, 09:24 AM
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#13
04-11-09, 04:56 AM
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Thanks OldGrouchy and furd. I counted the teeth of the cutters on my 1-1/4" die (ridgid), the shortest has 8 teeth and the longest of the 4 has 10 teeth. Using the chart in the book NJ Trooper linked to, it indicates for the 1-1/4" die that 11.5 teeth per inch as well as 11.5 teeth are required per end.
So given the 10 teeth equals 10 threads when flushed at the cutter ends, another 1.5 turns achieves the 11.5 threads required.
Still can't understand the need/concept to cut 2 threads beyond the cutter ends, all that is really accomplished is the taper moves up by 2 threads leaving the first 3 threads the same.
Thanks again.
So given the 10 teeth equals 10 threads when flushed at the cutter ends, another 1.5 turns achieves the 11.5 threads required.
Still can't understand the need/concept to cut 2 threads beyond the cutter ends, all that is really accomplished is the taper moves up by 2 threads leaving the first 3 threads the same.
Thanks again.
