NPT bottoming taps?

[mmcmdl]

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

Depending on the size ..............I have gages for NPT threads . You get to a point where taper taps are used and they are thread milled . They are still measured with gages to industry standards . All must be hydrotested for pressure also . If this this about harry home guy , run the tap in half way and check . The Teflon is not sealent , only for lubricant .

 

[RobertB]

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.

Yes, and the offshore manufactured ones in the big box stores can be particularly horrendous. It's not uncommon to connect two sections of pipe with a coupling or tee and have a few degree deviation from a straight line. If you look closely before buying you can sometimes see if the threads on the pipe/nipple are off but almost impossible to see it in a coupling or tee.

 

[Jake M]

Yes, and the offshore manufactured ones in the big box stores can be particularly horrendous. It's not uncommon to connect two sections of pipe with a coupling or tee and have a few degree deviation from a straight line. If you look closely before buying you can sometimes see if the threads on the pipe/nipple are off but almost impossible to see it in a coupling or tee.

If you make SURE to get a crooked threaded pipe, you can grab a bigger pipe wrench, you can keep cranking until the crooked fitting cancels out the crooked pipe.

Yeah, there is a LOT of absolutely inexcusable crap out there.

That's the biggest half of the reason I say (uncharacteristically) that you should NOT spend too much time looking for technical correctness on pipe threads. Get 'em engaged enough of course, but after that- 9 times out of 10 you're making one thread or the other to match existing parts that do NOT meet technical standards to begin with.

 

[WobblyHand]

Among the worst examples of NPT threads was the die set I got from HF. I threaded a whole bunch of 1/2" black iron pipe by hand, (for my compressor) only to find the male threads were seriously undersized and bottomed out on the US sourced fittings. None of them sealed. Freaking waste of time. Later, got some of my father's pipe dies (Rigid) and guess what, they were all true to size. Dunno maybe the HF NPT dies were made as "12mm" rather than 1/2", all I know is that they didn't seal at all.

 

[IHinIN]

I have tapped many NPT threads from 1/16-3/4 making air manifolds at work. Stopping 5-6 threads from the top of the tap works almost every time. Granted, we mostly use Parker and SMC fittings, not the pitiful crap from the big box stores.

 

[Flyinfool]

On all of my pipe taps I tie a piece of wire around the tap at the depth that I want to tap to. This way I know just how deep each tap needs to go to get good threads. That does not guarantee that a cheap out of tolerance fitting will work in the tapped hole.