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-