I have been using my Performax sander for over 10 years now and am
still learning about it. The main cause of the linear scratch marks
seems to be the old problem of not getting out all of the sanding marks
from the previous grit before moving up to the next grit. You can sand
to 220 grit, and have a very nice surface that requires only minimal
hand sanding. If you don't want to go that high, use the good old card
scraper. You can follow that with 220. It is a lot less work to scrape
a 150 or 180 grit surface than it is a 120 grit surface.
When running any boards through the sander, I always finish with at
least 2 passes on each side before lowering the sander again. I always
rotate the board to compensate for the sander not being parallel to the
bed, no matter how close I think it may set up. Also watch out for the
edges of the boards. They are very sharp and will cut you as you run
your hand up and down the board to feel how smooth it is.
robo hippy