Hi Guys,
Just a few more points when using a die on the lathe. If you are using a tailstock mounted die holder, make sure that there is no crud in the holder, stopping the die from being seated squarely. Quite often cutting oil will hold bits of swarf, so clean this out. To be sure, tap the die into the holder with a rubber hammer to seat it.
Another thing to check for is that the die is concentric, by this I mean some dies, even expensive ones, do not have the thread cutting part concentric to the outer. This does not matter if the die is turned by hand in the normal way but is does matter if the die is held in a tailstock mounted holder. It is for this reason that people have had to design (see old copies of ME, but don't ask me which issue)
tailstock die holders with oversize apertures and a fourth screw to centralize the die.
My own die holders have short handles, so that when threading under power, I can let go of the handle and it can spine freely. Cutting threads up to a shoulder is now easy, the die meets the shoulder and the handle pulls out from between finger and thumb and spins. It works rather like the screw-driving clutch on a cordless drill. Do though make sure that the saddle is clear when doing it this way, and don't try to cut too quickly, you don't want to overheat the die.
Ned