On Sat, 28 Jun 2008 22:10:49 -0400, "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

===========
Sometimes a taper tap in a straight hole without a guide can be a
problem. It may be helpful to use a taper reamer and then thread.
The thread quality will also be higher, and a taper reamed hole
is generally needed for dryseal quality threads.

for examples see
http://www.hermanscentral.com/produc...cfm?sid=google
http://www.use-enco.com/CGI/INPDFF?P...PARTPG=INLMK32
most mill supplies should stock.


Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).