: What thickness of glass works best?

I use plain old ordinary single strength house glass - probably 1/8 or 3/16 thick. I do keep a couple of pieces of 3/8 stuff around - and use if for really wide scrapers - as the thin glass has a tendency to break when wider than 3 inches. I am fortunate, as the local glass company guy is into boats and sailing so we have a lot in common. Usually he just has me help myself to the dumpster - but has been known to special cut a piece or two now and then when needed. Keep in mind, that if cut to a shape, it is similar to a big shaper blade.

Since I am also deep into R/C model boats, a piece of glass cut to a specific chord shape works great to fair the keel on the little ones.

The main things to consider ( thickness isn't one ) - sharp, fresh edge, and hold the glass almost perpendicular to the surface. Apply light pressure and pull towards you like a spokeshave.