Jon Elson wrote in
:

Other replies had much good info, but:


I set up the QC gearbox for 40 TPI, spindle for slowest speed (about
40 RPM), compound slide at 30 deg.

You might want to try threading at the highest speed you dare run at.
Since this is a very fine thread, you can probably do the threading
at several hundred RPM, at least.

I am turning to a groove at a shoulder. I am afraid that the tool will hit
the shoulder if it is too fast. I will experiment with higher speeds
though.


Right! Does it make a crunching or snapping sound when threading at
that end? If so, you may need either a tailstock center or a follow
rest to support the workpiece and keep it from climbing up over the
threading tool. Long, thin workpieces will try to do this, and you
can actually see the part jumping up and down as the threading tool
takes bites out of it. Even without the tearing, you'll never get a
proper thread when the work is flexing like that.

I think that the tailstock support is the first thing I am going to try.

Thanks for the suggestions Jon.

Rob