Jim Stewart wrote:

Jon Eiserling wrote:

I'm going to be threading the tenon of a rifle barrel and am
practicing on a 1" dia piece of scrap crs. The thread is 16tpi,
standard 60 deg. With the compound at 30 deg., 60 deg. threading tool
square/centered to the stock I keep getting an uneven finished thread.
The left side of the "V" is about 20 deg. and the right side about 40
deg. If I advance the cutter using only the cross feed, and not the
compound, I get a perfect thread.
I've tried setting the compound at 29.5deg, 30deg, etc. with no
improvement. I've checked the set-up with a protractor, dial
indicators, etc. and can find nothing wrong with the lathe or my
set-ups. Obviously something is wrong but at this point I don't have a
clue. Any suggestions?
Thanks...Jon.


I was having a similar problem. It turned out that
I actually had the compound set to 60 deg. rather than
30. I was following the marks on the compound and
they were either wrong or misleading....

You need to be set at 30 degrees relative to the
plane defined by the faceplate or 60 degrees relative
to the spinning axis.

IOW you want to be mostly advancing the cutter into the face of the V
that you're going toward, yet cut ever so lightly into the 'back' of the V.

Since thread finishes should be fine make lots of really light cuts, and
make sure that tool is sharper than sharp.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com