I've already built a few simple projects, but I find that the ignorance lingers, even as regards some very basic concepts. I learned a ways back (the hard way) that "modern" ply can't be sanded a great deal without the substrate peeking through. My error stems from '70 era high-school shop training that was better suited to solid wood, and the memory of older plywood whose top veneer was more than a few molecules thick.
So my question is this: How should I sand?
I'm considering building some plywood bookcases; tall (7'?) narrow (24" x 15"?) tower-shaped things to flank a wide window. Birch, or maybe oak. I've been told here that I need not start with coarse paper on ply, but I'd like some details.
I'd be using a very old third-sheet orbital sander. It's what I've got, and it seems to work well. The weight seems to damp some of the vibration too.
As an aside, what should I use for the backs, anyway? I'm sure 3/4" is not necessary, but what do you recommend?
As always, thanks in advance.