what drill for what tap

[Soundguy]

I will need to be drilling and tapping some cast for npt pipe fittings.

anyone know the drill sizes I'll need for 1/8 , 3/8. 1/2 and 3/4 npt taps?

want to have all the stuff at my shop before i start working on the project..

thanks

soundguy

 

[J35]

I will need to be drilling and tapping some cast for npt pipe fittings.

anyone know the drill sizes I'll need for 1/8 , 3/8. 1/2 and 3/4 npt taps?

want to have all the stuff at my shop before i start working on the project..

thanks

soundguy

Machinist Pipe Thread Tap - Drill Size Chart ANSI - Engineers Edge

 

[Soundguy]

Many thanks.

your 1st post and already you are helping out fellow TBN'ers.

thanks again.. exactly what i needed.

soundguy

 

[Hooked_on_HP]

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

 

[Soundguy]

well, it's a 3/4" taper per foot.

as for depth to tap.. not sure for 'average' situations.. i see most fittings have what looks like 3/4" to 1" of thread and that's it.

in the application I will be working on.. I will likely only have 1/2" or 5/8" of depth till I bottom out anyway.. so I won't have to do much guess work

soundguy

 

[sal64]

about 1/2 the top also if u have a countersink countersink the top of drilled hole before tapping makes it easer to tap.

 

[the bear]

good morning fellas if you all ready have a set of taps and dies there is a chart in the case to tell you which ones to use any good parts store also has the info you need

 

[Soundguy]

my tap and die sets don't have the chart. some of my taps do had drill size printed on them though.. not all of them do.

soundguy

 

[DieselPower]

You will have one in a few days Soundguy, I stuck the Starrett drill and tap guide in the mail for you today.

 

[3RRL]

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. For our mold and die work, we use the suggested tap drill size and then run a tapered pipe thread reamer in the hole until it bottoms out. Then tap it about 7 or 8 full threads. Depends on how deep you want the pipe thread to go in.

Always chamfer/counter sink the drilled hole before tapping. If you don't get the pipe tap reamers (one for each size pipe thread) consider drilling 1/64" over the suggested tap drill. We do that so as not to break the tap off. Our tool and die work is generally in tool steel so we always use pipe tap reamers. They are expensive but worth it to us because it saves the tap and getting a broken tap out of a blind hole can be costly. Also consider Moly-Dee tapping fluid when pipe tapping. There are other tapping fluids out there, but get a good one for pipe tapping.
Rob-

 

[Soundguy]

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]

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]

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]

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]

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

thanks

soundguy

 

[Soundguy]

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]

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]

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]

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

 

[DieselPower]

Got my quick ref pocket card in the mail today!

thanks again!

soundguy

No problem, glad I could be of assistance.