For slides, everyone I know uses the same type plywood I do. The dowel thing is actually an old woodworker thing, often using a metal threaded insert. I've used both in furniture but was timid about doing it with accordions because I was worried about not having enough room in the routed profiles of the frames. I didn't do it on my first one, which is made out of almost rotten cypresss, and had a lot of problems with screws stripping. After talking with Rusty Sanner, I tried it on the redwood one I made for Chuck with no problems, but went through on this little black one. It's a lot easier just to use a hardwood to begin with.