Mark

Thanks for the advice.

My taps do not have a female center in the back.

I did not countersink, the one that came out straight had a fairly long 1/2
inch counter bore that I am sure helped to keep the tap straight. I'll
remember the counter sink idea.

Yes I am backing the, but it seems to cut fine for about 2 turns and then
get tight. Thats when I back it off.

I have ground my own external threading tools, the nuts fit the threads
fine, I have no idea if they meet spec or not. Grinding for an inside
thread seems harder, maybe, I'll give it a try.

CarlBoyd

"chipswarf" wrote in message
...
Hi, Carl

Does your tap have a female center at the back? I think you'd be
better served, after starting the tap, to put a hard center in the
tailstock and use it to align the tap. Turn the tap with a wrench
while keeping tailstock pressure on the center. You can start the
thread this way also, and save your chuck jaws the beating they take
when the tap slips. Put a nice countersink in the hole before starting
the tap. I was taught this way when going through the USAF machinist
course in (gad!) '69.

You are backing off the tap every half-turn or so, to break the chips,
are you not? That greatly eases the job.

If you supply yourself, or make, internal threading tools, you'll
enjoy the results. If you doubt your grinding, you can start by
screwcutting with a pretty-good tool, and finish with the tap. That'll
provide better alignment, too. Have fun, I sorta envy where you are on
the learning curve. I had fun learning all this stuff.

Mark

On Jun 28, 9:10 pm, "Carl Boyd" wrote:
I have had a problem on a couple of my recent projects. Both involved
1/2"-13 inside threads. Both were cut with a tap on a lathe.

My procedure was to drill the hole on the lathe, and then hold the tap in
the tailstock chuck to start threading until the tail stock chuck slipped,
then lossen and slide back the tailstock, put a tap wrench on the tap and
finish by had. Two out of three times the thread ended up significantly
off
axis.

I had assumed that I would start the thread on axis with the tailstock
chuck
and it would stay on axis when I finished by hand.

What is a better procedure? I have cut a few external threads, but am
leary
to cut internals. I currently have no tools to cut internals threads but I
suppose I need some if that is the only way to do this.

CarlBoyd