Are you using cutting oil?
Are you advancing the compound at 30 degrees or straight in?
Heavy cuts or light cuts?

In article ,
Jim Stewart wrote:
I've been trying to cut 28 tpi threads in a length of
W1 5/8" drill rod stock. So far, they come out
ragged to the point of uselessness. I'm a bit
frustrated because the steel turns beautifully.

I'm using hand-ground and diamond-honed HSS+10%
cobalt tools. I've had good luck cutting threads
in brass, bronze and AL. I've also made passable
large form threads in steel.

Anyone have any pointers?