I've got the itch to put together a mortiser (woodwork machine),
and have some ideas about pulleys that will make a useful
one from (mainly) wood, not needing a strong column
for alignment.

The problem is, all mortise chisels use a 0.625" round
barrel, and they have to be clamped (not possible in
wood, this is a metal part), so as not to shift or rotate
in operation. The easy way is to make a sloppy bore
in cast iron, and tighten a couple of setscrews.

I don't particularly like that, though: the barrel gets
marred, and small adjustments become difficult.

So, how else can I clamp the chisel? Is it possible to just
buy something like an oarlock socket, with a tightening
mechanism? Maybe use a pair of V blocks with a hinge and
tightening screw? Or, one hemicylinder socket and a V block
opposing it?