SteveB wrote...
I want to spiral some small square stock. Probably 1/4" and 3/8" dimension.
What is the easiest practical way to do this? Hold one end in a vise and
twist the other with a crescent?

You've got the right idea. A blacksmith does this with a two-handled
wrench made for the purpose. A one-handled wrench, like a crescent
wrench, doesn't work as well because the side forces can't be avoided. If
you can't find or fashion a wrench with two handles, I suppose you could
try two crescent wrenches, but I don't know how difficult it would be to
keep them both on the work at the same time.

How do I keep the whole thing straight, or do I straighten it later?

You can keep it fairly straight if you use a wrench as described above,
but a little straightening is usually needed after also.

I want to spiral sections along a longer piece
rather than spiral the whole length.

No problem. It's commonly done this way.

And when I do want to spiral the whole length, will it spiral equally along
the length?

Not without care. By controlling the workpiece temperature carefully, in
particular making certain that the portion to be twisted is uniformly
heated, and by completing the turns quickly before the temperature
gradient becomes too pronounced, you can achieve a remarkable degree of
uniformity. With practice. (G) When the workpiece is much hotter in the
center, then the center of the twist will be tighter.

Check on www.anvilfire.com for better information. Tell them Jim der
junger sent you.

Cheers!

Jim