Tapping J-Pipe for 1/8" NPT Fitting

[2bclutch]

I drilled a hole in my J-Pipe ending with an 11/32" drill bit. The hole is way too small for a 1/8" NPT Nipple... but I do have the 1/8" NPT Tap. Is the Tap supposed to widen the hole enough for a 1/8" NPT Nipple or do I need to make the hole wider than 11/32"?

 

[oldman]

According to this chart as well as my own experience, 1/8-27 npt tap requires a drill size of .339". Since 11/32 = .34375, something is not right on your end.

 

[2bclutch]

The 1/8 27 NPT Tap fits into the hole fine. I think the fitting I have might be the wrong size. I'm going to post some pics of the stuff so you can take a look and see if everything is sized right.

 

[2bclutch]

Thanks for the info.

 

[mjarrell20]

It sounds like your fitting is off a bit, check into that and the pics would help.

 

[konicom]

the NPT is a taper thread. Its design is such that the actual process of tapping will enlarge the hole (given that the correct lead hole drill bit was used) creating a tapered profile. It is important to make sure the tap is not threaded too far as this will cause inadequate thread engagement and a loose fit (therefore leak). An unwritten rule is that during taping you leave approximately "three threads out" on the tap.
If infact you do have an 1/8 nipple - it will seem llike it will not fit if you're gaging it against unthreaded hole. Once threaded it will work.

Remember that the 1/8 nipple will roughtly measure 3/8" in diameter measured over threads
Hope this helps

P.

 

[oldman]

The hole should equal to the inner diameter of the fitting threads, if not, you have the wrong size fitting.

 

[2bclutch]

Well it looks to me if I start taping with the Tap and go until there are 3 threads left on the Tap then it would have to widen the hole.

 

[2bclutch]

The hole should equal to the inner diameter of the fitting threads, if not, you have the wrong size fitting.

The inner diameter looks to be the same as the hole that is drilled now. So my last question then would be could I use a Drill Press with the Tap?

 

[2bclutch]

Can I use a drill press to tap or do I have to use the hand tool?

 

[Auto RS T]

You definately want to do it by hand. When I was taught to tap you run it in until you feel a "resistance" then you back off the tap, and wipe/blow it off. Then repeat until you have the 3 threads left at the top. I think using a drill would strip it out. Take your time and use common sense.

 

[VelocitàPaola]

Keep pictures under 700x700 pixels please.