Richard J Kinch wrote:
Of course, I also want to use it as a random orbital polisher. I just
want to know if I can also use it as a sander in the way that I have
described above.

Sanding takes a lot more torque than polishing. Maybe it will stall too
easily, or won't keep the random pattern?

There are random orbital sanders, of course. High-horsepower gadgets.

According to the manufacturer instruction for Porter-Cable 7424
polisher, it is designed for both polishing and sanding. Moreover, the
spec of this polisher (such as amp) is identical to the spec of their
very similar sander/polisher (7336SP). Please see the spec shown he
http://www.porter-cable.com/index.asp?e=547&p=2804
Therefore, I am confident that it should be able to be used as a
sander. The only thing that I want to know is whether I can use it to
bevel a tapered edge alone the edge of a fiberglass skin.

Having said that, I have decided to choose Porter-Cable 7336SP instead
of 7424. The 7336SP comes with both polishing gears and sanding gears
in one package. And its sanding pad is 6" (instead of just 5" if I
convert 7424 into a sander). And the price is the same as the combo of
7424 plus the sanding pad. Thanks for questioning me about the 7424.
This leaded me into looking for the spec of 7424, and this in turn
leaded me to find 7336SP that is a better deal anyway.

Jay Chan