Cutting external screw threads with split dies

It'd work OK if it were full diameter before threading, but slightly less probably wouldn't hurt, and might make the job easier. Even if you only had 50% of full thread height, you'd still have 70% of full strength.

Threads that are cut, do not extrude.

At worst, a burr forms at the crest of the thread. That's just bad planning, though.

Cheers Trevor Jones

Unless you're aiming for 100% thread depth, you might want to allow for more than extrusion.

BugBear

Extrusion? If the die is blunt enough to be shaping material rather than cleanly cutting it you're in big trouble to start with. If you want a correctly formed thread then yes you need the stock diameter to be at least the nominal diameter of the thread you're trying to form. In practice a male thread will have a diameter over the crests slightly smaller than nominal or it won't go into a female thread that's exactly to size but you can let the die sort that out. It's obviously easier to finish with a fixed die than keep adjusting a split one until you get the thread to the size you want.

This may interest you - a novel (ish) use of a split die.

BugBear

Even better with the link (doh!)

adjusting a

You can apply the same technique to a die head as well and cut a wider range of o/ds than normal by adjusting beyond the graduatioons on the body of the die head. Handy for matching things like metric pitches and forms on Imperial stock as found on some machinery from the 1970's

AWEM

I think that it would become a square thread at that point.

Mark Rand RTFM

...no I see John as more of a Buttress .....

AWEM