I have not tried a belt sander on blades.
There are two alternatives in my shop. One is a 4 foot long hunk of granite on a tall horse with PSA backed 80 grit.
Here is the granite on the horse when it was first set up:
Granite on Horse.jpg
Gee, my shop was much less messy back then.
The other is the Veritas® Mk.ll Power Sharpening System:
http://www.leevalley.com/US/Wood/pag...35&cat=1,43072
Both are great assets for working blade backs and bevels.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)