For internal NPT threads, I've found lots of references that talk about running a tap in for twelve threads to get the proper fit. What's the math behind this?
How deep to tap NPT internal threads
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At work we use npt gages so there is some consistency from one person to another. At home I usually just buy a pipe plug the same size that I'm tapping and use it for a gage to determine how deep I need to tap the hole. Just use the "looks about right method" with the plug. It's cheap, simple, and works. Just the way I like it.Jonathan P.
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My old instructor's command is the "3 to 3-1/2 turns" thing. He told me to shoot for 3-1/2 turns, meaning: Tap the hole conservatively. Using a pipe plug, screw it in to finger tight, then count how many full turns it takes to pop out of engagement and be loose in your hand. When you have 3-1/2 turns, it's done.
I don't have any of the official gauges at home now, so this method is all I have. Thankfully, it seems to work.
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A little more looking yielded this:
"To achieve the basic thread depth, a machinist typically drives the tap into the workpiece 12 turns."
"The application, with proper gaging, will determine the appropriate depth for the proper mating of the parts."
From: http://www.ctemag.com/dynamic.articles.php?id=59Any products mentioned in my posts have been endorsed by their manufacturer.
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Originally posted by winchmanA little more looking yielded this:
"To achieve the basic thread depth, a machinist typically drives the tap into the workpiece 12 turns."
"The application, with proper gaging, will determine the appropriate depth for the proper mating of the parts."
From: http://www.ctemag.com/dynamic.articles.php?id=59
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Was taught to leave 5-7 threads out . Found out by gaging many many pipe taped threads that 6 thread will be just about perfect. so hardley even use gages any more.Every Mans Work Is A Portrait of Him Self
http://sites.google.com/site/machinistsite/TWO-BUDDIES
http://s178.photobucket.com/user/lan...?sort=3&page=1
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I've ran into this problem several times in the past. I also had a thread going a while back. I guess I'm not the only person that has problems with threadding pipe, or pipe threads. I have finally dawn the conclusion that plumbing is the art of cobbing, so just thread to fit.
JL.............................
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It's in the thread spec:
See, 5 turns there.
Since it's a tapered thread, it matters how many. Note the "hand tight" spec as well.
Cheers,
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5 still sticking out.
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