In terms of "flattening" wire to make bezel, you will want to roll
out SQUARE wire for this, and then you will have perfectly flat
edges. You are correct, if you roll out round wire to flatten it,
you will get a very irregular edge. I use the outer edge of the
flat roller, and leave a few millimeters of distance between the
edge of the flat rollers and my square wire I am reducing. I can
then visually guide the wire along the edge of the flat rollers,
steering it along the edge of the rollers to keep it straight.
A handy technique I've developed is to "pinch" the wire lightly
between thumb and forefinger, and place my middle finger in the
large "V" groove next to the flat rolls. As I roll the wire through
the mill, my middle finger slides along the groove, and the wire
slides between my thumb and forefinger, keeping the wire at the same
exact spot on the edge of the flat rollers.
Also, I only adjust the mill a small amount, perhaps 1/8 turn closed
for each roll, which helps keep the wire going straight.
I keep a B and S thickness gauge hanging between my mills on a chain
to check thicknesses of my stock while I roll.
---Jay Whaley UCSD Craft Center