New guy with questions

R

R_W_B

Registered
Registered
Joined
Jan 17, 2012
Messages
6
Hello folks, this is my first post I am a new guy. I am 62 yrs old, a semi retired civil engineering cad draftsman that enjoys doing my own mechanic work on my truck and motorcycle.

I have the following questions.

1. I realize that pipe threads are tapered, however I've only died the male threads on pipe ends before and have never taped any female pipe threads in anything. When I died the pipe ends I just ran the die on about 5/8 to 3/4 of an inch from the end of the pipe. I looked at a 1/4" NPT tap at the hardware store and noticed it's over an inch long. I'm curious do you continue taping it until the entire length has gone into the material ? Appreciate any info, I surmise answers to this will also tell me about correctness in chasing dirty or rusted female NPT threads.

2. Also I have an old tap and die set given to me by someone years ago. I see no taps or dies inside that are tapered like NPT. It appears to be just a cheap set of standard SAE taps and dies. However the labeled wording on the cover is confusing. It says,
" Courses National and Fine National and Pipe combination tap and die set ".
What could this " Pipe combination " term mean ?
 
Well, rearrange it a bit and it becomes Combination Tap and Die Set, National Coarse and National Fine. There should be a few pipe taps and dies in there, according to the description. Perhaps they are lost.

Oh, and in reference to the pipe tap.....there are tapered gages that have a flt ground on them that indicated the proper depth of tap. Most of the time, it is safe to tap until there are 5 threads showing above the surface. Don't go all the way in, it will be much too loose.
 
The letters NF, NC and NPT define the type of threads the tap or die cuts. National fine is usually a finer thread like 1/4X28 while a national Course is 1/4x20. Most tap and die sets include 1/8th and 1/4 NPT components. If I can I always run the tap or die all the way through, but that is just me. I always use teflon tape or pipe dope on anything with an NPT thread to prevent leaks and line up the fittings in the correct orientation. Welcome to the freindly forum and I look forward to seeing you around. We do love pics so take a few as you go and post em up.
Bob
 
Tony Wells said:
Well, rearrange it a bit and it becomes Combination Tap and Die Set, National Coarse and National Fine. There should be a few pipe taps and dies in there, according to the description. Perhaps they are lost.

Oh, and in reference to the pipe tap.....there are tapered gages that have a flt ground on them that indicated the proper depth of tap. Most of the time, it is safe to tap until there are 5 threads showing above the surface. Don't go all the way in, it will be much too loose.
Click to expand...

I suspect some must have got lost.

I thank you guys for all the replies. I did find searching around that the actual depth of taping pipe threads is somewhat optional, but to get the nominal size one should tape at least 12 threads into the hole. Taping more (or less) will cause the inserted threads to go deeper (or shallower).

Actually I'm not tapping anything new, but was needing to chase (clean) some drain plug threads on an engine and was curious about the length of the tap I saw for sale. I ended up just cutting 3 slots longways on the plug that came of the drain and used it to chase the threads clean. I then bought a new plug.
 
R_W_B said:
....I realize that pipe threads are tapered...
Click to expand...

Not all pipe threads are tapered.
There are parallell pipe threads as well.
Tapered threads rely on the wedging action of the 2 screwed parts being brought together, and the use of a thread sealant is recommended.
Parallell or straight pipe threads use a sealing washer, either inside the female part, that the male part bottoms onto. Or on the neck of the male part and seats down on to the collar of the female fitting. Additional sealant is not recommended.

Cheers Phil
 
Often, straight pipe thread (called NPS) in electrical work, on rigid conduit. Normally, it is for a mechanical rather than sealing joint.
 
You must log in or register to reply here.
Back
Top