How to call out a NPT Thread
How to call out a NPT Thread
(OP)
How do you call out a NPT thread length on a drawing?
I have a part that is 17.75 mm thick and I called out a 1-11.5 internal NPT pipe thread. The tap has a tapper on it, s if I don't tell where to the machinist to stop in depth with the tap, the hole will be over sized, so the NTP fitting will not thread in tight. Do you understand?
So how do I call out on a drawing, how much of the tep in length to us?
Frank
I have a part that is 17.75 mm thick and I called out a 1-11.5 internal NPT pipe thread. The tap has a tapper on it, s if I don't tell where to the machinist to stop in depth with the tap, the hole will be over sized, so the NTP fitting will not thread in tight. Do you understand?
So how do I call out on a drawing, how much of the tep in length to us?
Frank





RE: How to call out a NPT Thread
RE: How to call out a NPT Thread
17.75 mm is only slightly longer than the minimum recommended length of engagement for 1 inch NPT, so it is very likely that you will never get a good seal on this part.
RE: How to call out a NPT Thread
RE: How to call out a NPT Thread
RE: How to call out a NPT Thread
[IMG]http://i15.tinypic.com/2nv438j.jpg[/IMG]
Chris
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)
RE: How to call out a NPT Thread
Metric: ISO/DIN 228/1 (BSP, JIS B0202) parallel threads with appropriate O-ring or gasket.
Inch: SAE or MS 16142
RE: How to call out a NPT Thread
Frank
RE: How to call out a NPT Thread
To specify a shallower tap, just dimension it on the drawing, but make sure you talk to the machinist if you can to confirm that he notices it. I know, the drawing should speak for itself, but this is reality.
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
www.profileservices.ca
RE: How to call out a NPT Thread
Whichever way you go, with NPT fittings it is advisable to use teflon tape or other sealing substance to help achieve a seal.
RE: How to call out a NPT Thread
AND as Mr. CorBlimeyLimey pointed out they do make a straight nation pipe thread (NPS)...this is the stuff you'll find on electrical conduit and conduit fitting. This is NOT the normal threading for pipe that you don't want to leak.
...AND Mr. MintJulep my friend, you would not do well here in U.S.A. oil field environment! *L* …Good Luck all! …Mark
RE: How to call out a NPT Thread
MintJulep,
NPT definitely has it's applications. I'm interested to know what could be used in it's place in a plumbing environment.
Powerhound
Production Supervisor
Inventor 11
Mastercam X
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: How to call out a NPT Thread
11echo ... I have assumed that your response was intended as being somewhat playful considering the *L* & *G* usage, so I have scaled back my initial knee-jerk response;
First Mistake; (Making guesses)
"...Let me guess most you guys are LIMEYS ...Huh!!?"
Was there a point behind this comment?
Second Mistake; (Not reading the OP correctly)
The 17.75mm dimension was referring to the thickness of the plate to be tapped, not the nominal of the pipe thread.
Third Mistake; (Math)
Well actually you did the math (conversion) correctly, unfortunately you converted the wrong thing.
Fourth Mistake; (Forum Etiquette)
Criticising other posters contributions without contributing a damn thing to help the OP.
The OP stated that the pipe thread he wanted to use was 1"-1.5 which is 1.327" actual O/D and has an effective thread length of .682". (Yes, I can read a chart too.) The .682" dimension by the way is 17.32mm, which is why your "friend" suggested that the 17.75mm thickness might not yield a succesful seal.
BTW, straight NP threads are also used on many regular pipe fittings (valves, elbows, connectors, etc) ... not just conduit types.
Also, the OP mentioned "NTP fitting" not pipes.
For future reference, my handle is CorBlimeyLimey (or CBL for a more user-friendly reference) not "Mr. CorBlimeyLimey". IMO, the "Mr" title (in the context you used) came across as being condescending ... but then I do have an intense dislike of titles so that could just be me.
RE: How to call out a NPT Thread
I too had to go back and edit my original response to 11echo's post as I figured 2 wrongs would not make a right. I decided to post something potentially helpful instead of critical of others' contributions.
As far as location goes, I live here in the USA but am, by no means, a "roughneck". I still have all my fingers and teeth.
Powerhound
Production Supervisor
Inventor 11
Mastercam X
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: How to call out a NPT Thread
RE: How to call out a NPT Thread
First of all, congratulations on the birth of your Grandchild. Is it a boy or girl? Either way I hope you will have as much fun with him/her as I am having with my grandkids.
Just to clarify things, I didn't and don't take offence at being called a Limey. How could I with my handle?
As for the "Mr" thing, well as I wrote before, that's probably just me, but given the overall content of your post, I interpreted it as being condescending ... especially when followed by your derogatory opinion of MintJulep's competence and the "my friend" reference. Unfortunately the "intonations" of the written word can be all too easily misinterpreted.
Anyway, please accept my apologies if my response detracted from the enjoyment of your happy news.
RE: How to call out a NPT Thread
AGAIN my humble apologies for a “lame” attempt at humor …AND my best wishes for a merry holiday season!
RE: How to call out a NPT Thread
I don't know what sort of volume you are running, but a 1-11.5 NPT plug gage would only run you about $150 USD. That will control your depth.
RE: How to call out a NPT Thread
Do you really need to call out the depth of the NPT tap?
Any machinist should know how deep to tap the hole to get a proper fit on the thread.
Your job on the drawing is to define what you want.
The machinist's job is to make the part to your design.
By only calling out the NPT thread on the hole, you have done your part. How deep the machinist taps the hole to get the proper fit, is his job.
"Wildfires are dangerous, hard to control, and economically catastrophic."
Ben Loosli
Sr IS Technologist
L-3 Communications
RE: How to call out a NPT Thread
Powerhound
Production Supervisor
Inventor 11
Mastercam X
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: How to call out a NPT Thread
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
www.profileservices.ca
RE: How to call out a NPT Thread
David
RE: How to call out a NPT Thread
Most fittings stick out sufficiently
that it is very hard to over tap the
holes. Just curious why you are calling
out such a large pipe tap. Won't a
smaller pipe plug allow just as much
grease to be supplied per hole?