Engine/Transmission (1998.5 - 2002) drill size - wrong forum

[Texas Diesel]

I know this is the wrong forum but dont know where to ask general mechanical questions.



What size drill is need by 1/8" PIPE THREAD tap?



TIA

 

[B.G. Smith]

Drill size

The correct drill size for use in drilling a hole to be tapped to 1/8" pipe thread is a letter drill, R. The diameter of this drill is . 3390, the next smaller drill is also a letter drill, Q, diameter, . 3320 The next size larger drill is 11/32", . 3438. bg

 

[jlccc]

https://www.turbodieselregister.com/forums/showthread.php?threadid=53985



Is the link you want.

 

[Texas Diesel]

Amazing, ask an off the wall question at midnight and get answers



This is better than Dr Laura

 

[B.G. Smith]

Drill size

And no, there are not several correct sizes of drill to use to tap a specific size hole, it depends on what you want and what you are doing. If it is critical and you want it right the first time, there is usually only one. They used to ask me "Why is there never enough time to do it right the first time but always enough time to do it over?"

 

[LarryB]

That's because you don't alway know what the right way is until you've done it wrong.

 

[jlccc]

Re: Drill size

Originally posted by B. G. Smith

The correct drill size for use in drilling a hole to be tapped to 1/8" pipe thread is a letter drill, R. The diameter of this drill is . 3390, the next smaller drill is also a letter drill, Q, diameter, . 3320 The next size larger drill is 11/32", . 3438. bg

Let me disagree without being disagreeable.



The 'R' letter drill is for NON-TAPERED pipe threads. For TAPERED pipe threads the 'Q' letter drill is the correct size for use without a reamer. For use WITH a reamer the suggested size is 21/64". My reference is the 9th edition of Mark's Standard Handbook for Mechanical Engineers. I think you will find that a "Machinery Handbook" will confirm what I have said.

 

[JWhitcomb]

Just a personal thing but I always try to use a tapered reamer when I use a pipe tap. It always makes me feel more confident about leaks if a truly tight thread is needed. Never have to use teflon tape with this method.