Pipe Threading Q

bmwpowere36m3

Hey,

I'm threading some 3/4" black pipe for a gas line. I borrowed my dad's old Rigid 3-way hand threader. I ran the threader till the cutter was flush with the end of the pipe. The finished threads seem to be short, i.e., as compared to a factory applied thread on a nipple and 10' stick.

So my 3/4" threads are ~9/16" long and I can thread on a fitting by hand ~ 2.5 turns. Whereas the factory threads are 3/4 to 13/16" long and the same fitting can thread on 3.5 to 4.5 turns.

Should I be running the threader deeper into the pipe? Thx

bmwpowere36m3

Hatterasguy said:

Yes.

4.5 turns until hand tight on 3/4".

Maybe I'm over-thinking it...

Won't running it in deeper (cutter end going past the end of the pipe) start to produce straight threads at the beginning?

STEVEusaPA

http://www.piping-designer.com/index.php/disciplines/mechanical/84-stationary-equipment/fastener/1156-national-pipe-thread?title=National_Pipe_Thread#ixzz3olfKwEcS

bmwpowere36m3

So just thread it deeper then :-)

Simple. I just thought the cutter was supposed to stop at the pipe end. Maybe the newer ratcheting or powered cutters have longer dies...

rick in Alaska

I have always used three turns for my setups, so have never been around any that were 4.5 turns. Seems like a lot, but I guess I have never actually looked at the proper charts. Just what I was taught>
Rick

ChrisJ

Are you sure the die your using is NPT?

bmwpowere36m3

Hatterasguy said:

bmwpowere36m3 said:

So just thread it deeper then :-)



Simple. I just thought the cutter was supposed to stop at the pipe end. Maybe the newer ratcheting or powered cutters have longer dies...

Actually, after reviewing it, your first thoughts were correct.

There is no good reason to thread it deeper if you have run out of die length. You will produce a straight thread for the distance that you go past the end of the pipe.

And, when you couple it up, the straight thread could present issues if it jambs before the tapered thread jams.

So, to get the specified number of turns, you do need a die of sufficient length. Otherwise, you live with what you have.

I called Rigid this morning to inquire about their threader. Response was to basically to stop when the cutter reaches the end of the pipe and factory-applied threads are longer than those done with manual threaders (CNC?).

I'm going to leave them be.

bmwpowere36m3

ChrisJ said:

Are you sure the die your using is NPT?

Yes

hot_rod

My guide was to allow one thread out past the end of the die. That assures you have all the taper cut, and not excessive straight section.

EBEBRATT-Ed

Common sense works best. Take an elbow or a coupling and one of your newley cut threads dope it and make it up tight and look inside the fitting. Is it all the way in??

One thread short or one thread long is no big deal. but you want to engage all the threads in the fitting if possible

bmwpowere36m3

Finished threading and putting in the gas line. Everything went well. I didn't thread the pipe anymore, maybe 1 turn past the end.

About 5 turns fully tightened up with Rectorseal. The pipe definitely didn't go all the way into the fitting... but I'd just be making straight threads with my threader.

ChrisJ

You don't want the pipe threading all the way into the fitting, this would suggest bottoming out.

I usually expect to see 3 threads or so showing. I have a few with more showing. I'd say 4-5 turns is a good amount for 3/4" NPT.

When tightening, I go until I feel it start to bind. That is, it will feel like it's tightening smoothly, slowly getting harder with each turn and then it feels as if it gets super tight all at once, that's the sweet spot. If I can't hit that without it bottoming out, I consider it a bad joint and somethings wrong with either the nipple or the fitting.