what drill for what tap

Soundguy · May 17, 2009

I've used my die's and taps alot.. but they have all been straight thread apps. i'll be tapping some NPT hopefully on monday if my work material comes.

I'll keep the slight countersink in mind before the tapping.

soundguy

kayco53 · May 17, 2009

Hooked_on_HP said:
When tapping tapered pipe threads how far in do you run the tap.
Bill

In the shop we usally have the fitting or pipe to try that we are going to screw in. You
don't want to tap to deep because the thread is tapered.We like to maybe 3 or 4 threads
showing when tight.Depends on size of course.I think its about 3 on 1/8"npt and about the same on 1/4.Try one and it will thread in and look right when it is.I'am sure there is a chart but I couldn't find it at home.
1/8 is 21/64
3/8 is 37/64
1/2 is 23/32
3/4 is 59/64 these are from the starrett chart.
Remember to use tapping oil.

DieselPower · May 17, 2009

3RRL said:
Chris,
The Machinery's Handbook is great.
You can also get small pocket size drill and tap charts at almost any industrial tool supply place. They are usually give aways.

He doesn't need to worry about tracking down one of the pocket cards, the machine fairy dropped one in the mail for him today.

3RRL · May 17, 2009

DieselPower said:
He doesn't need to worry about tracking down one of the pocket cards, the machine fairy dropped one in the mail for him today.

Way to go Diesel, those things are mighty handy.
In our shop we used to get the large wall size charts from suppliers (I could read them without my glasses

) We had them posted all around the tool crib and machine aisles. The used to give them away too but I believe you have to buy those anymore.

Soundguy · May 18, 2009

Yeah, thanks again.. can't wait to get mine int he mail.

thanks

soundguy

Soundguy · May 18, 2009

DieselPower said:
He doesn't need to worry about tracking down one of the pocket cards, the machine fairy dropped one in the mail for him today.

Got my quick ref pocket card in the mail today!

thanks again!

soundguy

scott_vt · May 18, 2009

kayco53 said:
We like to maybe 3 or 4 threads
showing when tight.Depends on size of course.I think its about 3 on 1/8"npt and about the same on 1/4.Try one and it will thread in and look right when it is.I'am sure there is a chart but I couldn't find it at home.
1/8 is 21/64
3/8 is 37/64
1/2 is 23/32
3/4 is 59/64 these are from the starrett chart.
Remember to use tapping oil.

Good Afternoon kayco53,
You hit the nail on the head, I used to use that method and when I went to get the pipe thread gage, it all most allways was the proper depth !

Tractorguy1038 · May 18, 2009

Hooked_on_HP said:
When tapping tapered pipe threads how far in do you run the tap.
Bill

For what it's worth: 1/8th pipe has (theoretically) .264" of "effective" thread. 1/4 has .402". 3/8 has .408. 1/2 has .534. 3/4 has .546. These numbers apply to American Std Taper Pipe per American Machinist Handbook. < chuckle >

Soundguy · May 18, 2009

that's good because the flange I'm tapping is probably .4 to .5 inches thick.. max.. and I'm planning on going 1/4 pipe. would have liked to do 3/8 pipe.. but just doesn't look to be enough metal left over in the end of the boss I'm drilling thru... would only leave about 3/16 wall after drilling.. then threads will eat up some of that..

soundguy