Proper diameter drill rod or bar stock for threading?

[quick toy]

I have a question about threading.
I'm running into some problems during threading. I want to make some 3/4 - 16 stubs. Should I be using .750 drill rod or .740 bar? I noticed that with the drill rod I end up overcutting the threads to get it to work.
Is there a chart or formula I should be using, or is this just novice operator error?

Thanks,
Paul

[Geof]

You will find this sort of thing in Machinery's Handbook but if it is a non-critical application going a bit below nominal and getting a flat crest on your thread is probably okay. I would use about 98% of the nominal diameter.

Your choice of drill rod I would query; it can be a pain to get a good finish in the annealed form. If strength is not an issue use leaded steel, 1018 or 1045 if you do need something stronger.

[quick toy]

Thanks Geof

Paul

[in2steam]

I have a question about threading.
I'm running into some problems during threading. I want to make some 3/4 - 16 stubs. Should I be using .750 drill rod or .740 bar? I noticed that with the drill rod I end up overcutting the threads to get it to work.
Is there a chart or formula I should be using, or is this just novice operator error?

Thanks,
Paul

Are you using HSS or crabide? carbide tends to bit into drill rod a little more and results in that problem, as sugested try 12L series instead.

chris

[quick toy]

HSS
Thanks for your input.

Paul

[imfamous_one]

for threading you should cut the major diameter .005" smaller than the thread size, so for 3/4 16 .745" would be fine. .740" wouldn't make too much difference as long as you check the thread with a nut to make sure you don't cut too deep and make the thread sloppy. Oh and don't use drill rod... that stuff is hardened and will be super hard even to face.... let alone threading. Just use regular cold rolled. If strength is not as high a concern C12 has high lead content and machines really easy, and leaves a good finish.

[jhowelb]

Here is a chart that may be of interest.