Pipe tap to small

[dr sportster]

Tap sizing standard then +.0005 is H1 then >0005+.0005 = H2 .001 bigger then H3 is 3 x >0005 and so on . Does this apply to pipe taps I can 't find any listing of an H size on any pipe tap ads. Reason I ask is
I tapped a hole 1/8-27 and my pipe plug won't fit Before I moved I had many sizes of each pipe tap which got lost in the move . Some just cut more than others My tap does not cut enough to screw into.

 

[Steve@Advance]

I assume you're talking taper pipe. If so, no oversize, just run the tap in further.

Generally leaving about 6 threads showing is a good starting place.

Are you sure the plug is not British thread?

 

[dr sportster]

No stadard taper 1/8-27 NPT tap is bottomed in part {yes I know that trick }

 

[timcasbolt]

(quoted from post at 19:14:37 09/02/22) No stadard taper 1/8-27 NPT tap is bottomed in part {yes I know that trick }

f I'm understanding correctly, you should be able to grind off the end of the tap so it will go in further.

 

[TimV]

Agreed--we had to do that in the dairy barn as otherwise the spigots for the vacuum lines wouldn't thread into the pipe--a normal-length tap would hit the other side of the pipe before making a large enough hole. Cut off an old tap and always used that one for that job. Much like making a 'poor man's' bottoming tap when you don't have a factory-made one by cutting off the tapered bottom portion of a standard tap, which I'm sure many of us have done in a pinch.

 

[leroy in ne]

They do make what is called a short projection tapered pipe tap. Some call this a bottoming tap. these are used to tap shallow blind holes to gage dimension. How ever if this is a one time limited use deal, others suggestion of tapping as far as possible and grinding a few threads off length to get to large enough diameter.

 

[dr sportster]

I thought of grinding it shorter but did not want to ruin the tap. It seems the only solution .

 

[wore out]

(quoted from post at 07:48:15 09/03/22) I thought of grinding it shorter but did not want to ruin the tap. It seems the only solution .

If it is a quality tap and you don't want to modify it you can buy a cheap tap for $ and up on fleabay and keep yours intact.

Seems like an easy solution?

 

[Roger Tomfohrde]

NPT pipe thread is a tapered thread. Supposed to be 7 continuous threads is considered a fully tapped hole. So if it does not start you have not cut the threads deep enough. It gradually gets tighter as the male section is screwed in.

 

[dr sportster]

Got an Irwin tap at Ace hardware and it was bigger and cut deeper threads without grinding.