tap 1/2" in steel

You're the one that is spouting ignorance, and encouraging ignorance, probably so you don't appear quite as stupid as you really are. There aren't any "black arts" to cutting threads, it's step by step by step, and very damn simple steps at that. I don't know where you are, or who you work for, but around here, you walk into a job shop and a week later they find out you can't cut threads, competently, you walk out and resume looking for a sweepers job. A busy jobber hasn't got time to hold your hand, either you know what you're supposed to, or go looking for work again. Better look for a drone position in a factory on production, they rarely single point anything.

To the original poster, don't let any of this discourage you in any way. For what you want to do, a tap is perfectly acceptable, and I don't object in the least. Your question was legitimate for a newbie, but the remarks from larson_tools were totally ridiculous and false. If you can see it to take the lathe course, do so. If nothing else, you will understand the process when you're done, and after seeing the possibilities that it opens to you, it may well be the one thing that pushes you into a lathe that does have threading capability.

Adding to your skills and advancing your knowledge is NEVER something "best left to the geeks and old germans." The geeks don't know how without their silicon brains, and the old germans f*ck up just as often as everyone else. Learn, Learn, learn, and pretty soon instead of asking questions, you'll be answering them.

Fink, the only way you could really hurt me with your ad hominem diatribe is to print it, roll it up and stick it in my eye.

(There, it should take him at least a day to borrow a dictionary. he he he he he..... ;-)

larsen gets to snuggle up to gunner in my idiot file

Sure, I see what you're saying. That seems like a very good idea. I think the Sherline would be rigid enough.

Especially since I think I'm going to end up doing this in brass rather than steel, so it should be pretty easy to tap :-)

If you go easy, the sherline will probably be enough machine to tap 1/2 inch fine thread even in steel. The key is to not try for

100% thread depth. Read up on what minor diameter gives 50% thread dept for that size, and go that route. Also turn a generous chamfer on the start of the bore.

Use plenty of cutting oil if you do it in steel. You won't have any trouble. The lathe is basically being used as an alignent fixure to get the tap concentric with the bore of the hole. Use a good quality tap, not just some hardware store junk. It should say HSS on it and be ground all over.

Jim

Yes ! Well good stuff. Hope it works for you. I do like Jims suggestion to go with national fine, if you can, and the suggestion to go with something less then 100% thread depth is brilliant. (scalled experience)

Speaking of experience, one of the things I did out of frustration when I started was to buy into just about every available size NC cap head screws and it proved to be a good investment. However a few years go I got speaking to a smart young guy that ran a successful prototyping shop and one of the things that he passed along were the merits of using NF wherever possible because of the ease in tapping. Unless otherwise specified he does everything in NF and he can do most of the tapping with a variable speed drill. (time is money) I now have an excellent selection of NF cap head screws.

Again, Good luck!

Bill

There's also the minor factoid that for the same size screw, NF is stronger than NC. Tends to seem "wrong" at first, but it's true.

That's interesting. Is that a handbook kind of figure? and what's the explanation of this counter-intuitive result?

Boris

I think it depends on the material. Fine threads in soft metal are not as strong as coarse threads.

It's not the thread that's stronger, it's ultimately the bolt that is stronger. The deeper NC thread cut makes the bolt snap easier...

I assume it would apply differently to an inside thread, but the inserted / threaded rod / tool / bolt would have to be considered as well.

More cross-sectional area left in the bolt (larger root diameter).

Except in extreme cases of material strength mis-match (like steel bolt in plastic hole/nut) the limiting factor with proper thread engagement (~1 diameter, IIRC, but I may not RC) is the core of the bolt, not the threads.

It's a factoid I recall from one of my practical machine shop courses, but a quick look into the bolt reference guide someone mentioned here a while ago confirms it (10-24 and 10-32 are both listed with failure torques in theaded holes of various thickness, and the 10-32 numbers are consistently higher).

CLIP

Well said.

The really instructive case is for 6-32 vs 6-40

Jim

As usual the answer depends.... NF has a larger minor diameter so the bolt is stronger..............provided that the thread engagement is long enough that the threads don't strip out. At least that is what I think. I ought to go back and do some more reading on Bolts.

Dan