"Darrell Feltmate" wrote in message
news:YwnEd.70613$dv1.48262@edtnps89...
Bruce
the belt sander works "well" because it so fast that the 80 grit does not
get a chance to work as 80 grit. The tips of the grit are all that get a
chance to touch the wood, not the sides, so the paper does not have a
chance
to remove as much wood as it ought. We use a coarse grit to remove the
necessary damaged wood and leave the good. A belt sander moves too
quickly,
generates too much heat, and leaves a case hardened surface. It is good
for
removing wood quickly but should be started with a lower number grit than
usual.

Torn fibers pack between the grains and heat/burnish the surface because
they aren't ejected as they are created. That's why rotary power sanders
work so much better than holding a piece of paper against your bowl as it
rotates - they can unload themselves to a much greater degree. But take a
hint from the directions on your Random Orbit Sander - don't press.