"sbnjhfty" wrote: Being an amateur... Why reverse for sanding?
^^^^^^^^^^^^^^^^^^
I asked my son's shop teacher that question, and he said, "Just reverse the
sandpaper." He was just kidding.

When you sand, there are little wood fibers, like hairs, that all get laid
down in the same direction, and not removed. When you reverse the rotation,
these "hairs" have to flip over, and lots of them get taken off. If you
reverse a few times, most of them will get gone. If you apply lacquer
sanding sealer to the surface, it binds these hairs, so they can't do their
flip-flop, and they get removed sooner. (This is my theory--I can't
actually see what they're doing.)