NPT bottoming taps?

[markba633csi]

Is there such a thing? I always seem to miscalculate when using NPT taps. The recommended drill sizes always seem too small,
and I usually have to run the freaking tap about a mile deeper than I thought I needed to- this seems to bite me every time
The tap should have a mark on it showing how far to go IMO
It appears the tap needs to go in more than half of the way to make a usable thread and it doesn't seem possible
with the recommended tap drill
I don't know what the secret is but I have yet to figure it out completely

 

[Nesse1]

NPT is tapered. I usually tap and trial the fit a couple of times, until I'm happy with the engagement. Learned from the school of hard knocks to not tap too deep first try.

 

[RJSakowski]

One trick when using taper taps is to drill a stepped hole. The bottom or thru hole should be the recommended tap drill size but if you drill a shallow step a few thousandths larger, it will be easier to start the tap. If you need to tap a blind hole as in a EL fitting, the tap will often bottom out before the thread is deep enough. You can start the tap as usual but finish with a tap which has been ground short.

In my experience, tapered pipe fittings vary from one to the next. I usually make my initial cut shallower and check with the intended fitting. From there, I decide how many more threads I want for engagement and run the tap again accordingly. If you have multiple hole to tap, you can mark the tap with a marker.

 

[woodchucker]

Stepped drilling. And a taper reamer for NPT. The reamer is a hand reamer. Air on the side of too tight. Then do a 1/4 turn at a time.

 

[piper184]

And, remember that hardware store pipe fittings are often, shall we say, less than optimal fabrication. I quite often have to "tune up" the threads to get proper engagement.

And every now and again I find a female thread that was tapped too deep from the factory. Those are the hardest to fix.

 

[Jake M]

Is there such a thing? I always seem to miscalculate when using NPT taps. The recommended drill sizes always seem too small,
and I usually have to run the freaking tap about a mile deeper than I thought I needed to- this seems to bite me every time
The tap should have a mark on it showing how far to go IMO
It appears the tap needs to go in more than half of the way to make a usable thread and it doesn't seem possible
with the recommended tap drill
I don't know what the secret is but I have yet to figure it out completely

Pipe threads are not bolt threads. It's a taper, there's "fits", the mating part (unless you make it) has unknown tolerances... It's a jungle.

The best thing you can do is keep track of your taps. If "most" fittings go into the hole OK at ? Half showing, 5/8 showing? Whatever number of threads showing... Well, that's a start.......

A bottom tap? Never seen one, but if you're trying to get EXACT fits.... It's hard to push these to be "too" exact, as each time a thread is taken apart and reassembled, it's not gonna finish in the same place.... I wouldn't want to see the bottom of a threaded hole that was very close to the end of the fitting..... But if you needed to shorten the tap, or make a true bottom tap,... You've just got to remove the excess, without ruining what remains. That's about all there is to it.

 

[extropic]

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[mmcmdl]

Taper reamers and pipe tap gages are used in industry .

 

[toprecyler]

I’ve heard that there are tapered reamers that should be used before tapping a NPT hole.

Now, I work in a Hydraulic rebuilding shop, that’s been in business for 30 years. It was started by several guys that each had 5-30 prior experience too. We do not have these tapered reamers. And probably if I asked for them, I might get “ we’ve been doing it this way for 30 years. Why change now”.

And to be fair, I probably use a NPT tap less than once a month. Honestly,other than 1/8” pipe tap for grease zerks, that is. But I have ground the bottom of a tap to make a bottoming tap before. Needed to clean out a fitting, and had only so much room to work with.

So that said, I was told years ago you should be able to easily hand tighten the fitting in 2-3 turns before it starts tightening up.

In theory, you do not need any lubricant, sealant, or Teflon. The metal to metal threads are supposed to do the sealing.

I also had heard that most of the purpose of thread sealant/ Teflon tape was really to act as thread lubricant so you could tighten the threads tighter without the threads galling each other.

Some of these thoughts do sort of make sense to me.


Sent from my iPhone using Tapatalk

 

[RJSakowski]

I’ve heard that there are tapered reamers that should be used before tapping a NPT hole.

Now, I work in a Hydraulic rebuilding shop, that’s been in business for 30 years. It was started by several guys that each had 5-30 prior experience too. We do not have these tapered reamers. And probably if I asked for them, I might get “ we’ve been doing it this way for 30 years. Why change now”.

And to be fair, I probably use a NPT tap less than once a month. Honestly,other than 1/8” pipe tap for grease zerks, that is. But I have ground the bottom of a tap to make a bottoming tap before. Needed to clean out a fitting, and had only so much room to work with.

So that said, I was told years ago you should be able to easily hand tighten the fitting in 2-3 turns before it starts tightening up.

In theory, you do not need any lubricant, sealant, or Teflon. The metal to metal threads are supposed to do the sealing.

I also had heard that most of the purpose of thread sealant/ Teflon tape was really to act as thread lubricant so you could tighten the threads tighter without the threads galling each other.

Some of these thoughts do sort of make sense to me.


Sent from my iPhone using Tapatalk

NPTF or Dryseal pipe fittings don't need a sealant. NPT fittings need a sealant.