I got an old Rockwell TS last year, and it has never ripped thin boards
perfectly straight--they always came out slightly banana-shaped.
Last night I was making the fence for a drill press table, and it
finally pissed me off enough that I decided to figure out what it was
and fix it.
Turns out that the fence thickness varied, and was substantially thicker
at the front and back than it was in the middle. This ended up giving
the effect of a curved fence, which thin boards would naturally follow.
I ground down the steel fence front and back, then cut a scrap of
melamine to size and screwed it onto the fence, shimming the middle out
with enough layers of paper to bring it flat.
Works great, and now I'm kicking myself for not doing it sooner.