I just made female threads on the lathe for the first time.
I used a boring bar with a 60 degree bit that I ground.
I have a book "Machining Fundamentals" by John R. Walker that explains
how to grind the bits and operate the lathe to make the cuts.
I ignored the book and made some on my own, but I got left hand threads.
It is easier to just follow the directions.
Not exactly an answer to you question, but if possible, as you approach
finished thread depth, stop and test fit (without taking the part out of
the chuck). Then just take light passes until the fit is what you want
it to be by feel. Make sure the thread are clean when you do this.
Of course, this does not work when one part already exists and is too
big to bring near the lathe. Also, I'm assuming this is hobby work and
the exact clearance is not critical.
It's better to be a red person in a blue state
than a blue person in a red state. As a red
person, if your blue neighbors turn into a mob
at least you have a gun to protect yourself.
As a blue person, your only hope is to appease
the red mob with herbal tea and marinated tofu.
I read the books I could find and still couldn't figure it out till I
threw the books aside and said screw it, it looks like I'm just going
to have to wing it and it worked the first time !
I'm perplexed that in the information age why computers are like
stabbing in the dark.
That's what I do, try it. Lately, I'm cutting an internal sort of
acme thread, 3/4" x 5tpi. "Sort of" because it is intended to fit mop
handles, and they are NOT precise, at least to thread form, depth,
etc. So I chopped off a $1.95 broom handle with a metal tip to test,
then removed and tested on another handle with a plastic tip. Oops,
have to break the edge and open up the i.d.
Picking up the thread again wasn't too bad. I just stuck the piece
back in the collet, engaged the tool in the thread with the crossfeed
with the boring bar loose and the threading dial at the right spot,
then clamped the boring bar. To set the threading dial, I disengaged
the drive and rotated the spindle (with the tool retracted out of the
threads, of course).
I followed a suggestion I believe I read here a while back, and
threaded in reverse on the back side. It worked very well, because
the carriage travel was left to right, or out of the bore. At 5 tpi,
it moves pretty quick, even in back gear.
Machinery's Handbook, or any other machinist's handbook will give you
exhaustive information on thread turning. In general, I use a couple of
thou. for clearance, but it makes a very tight fit. The class of the
thread, based on strength requirements and size determines the
It's a good idea to stick with published standards for
What's an even better idea is to learn to properly apply thread wires so you
can stick to the standards. They are of no use for internal threads, but
perfect for outside measurements, and cheap to own. For those that don't
understand, wires are the proper way to measure threads, and are used for
calibrating thread gages. There is no better method.
I have some information on using three wires on my web pages
These web pages have been shamefully neglected for far too long but I
plan to converto to a "rreal" web presence soon and will update and
improve things on the pages.
Instructor, Machine Tool Department
H.H. Ellis Technical High School
643 Upper Maple Street
Dantieson, CT 06239
New England Model Engineering Society