: Yeah, but how do the joints look? Is this one of those it won't matter in the
: end things?

That is corect.

You would be sanding, or planing, wood from an area that would be hidden. These areas will be the inner parts of the joint, and obscured by the glue that joins them. The visible part will be the outer skin of the plywood, so you don't want to cut into that more than a millimeter or so -- preferably not at all -- if you can help it.

I don't think there is anthing magic about an exact 45 degree angle here. I'm sure anything between 30 and 60 degrees would work just as well. All you are doing is removing the wood which will get in the way of drawing the panels tightly together so the outside skin on one panel can contact the outside skin on the adjoining panel.

For tool cost, go with making a rig to hold sandppaer: one block of wood, a sheet of sandpaper, and two thumbtacks to keep the sandpaper on the wood block. For speed go with a hand plane. For more speed you can use many different powertools to change the edge of that plywood from a 90 degree angle to a 45 degree angle. Routers and shapers would do the job in one pass. A router bit chucked into a drill press would do the same thing, but need a slower feed rate. You coule also recut things with a table saw or curcular saw. if you didn't wnat to cut things, you could use a sanding disk on either table or circular saw, se the angle at 45 degrees, and feed snad away the excess. An orbital sander could be held at about a 45 degree angle and you could create the edge freehand. (just keep the thing moving; with no fence on it there is a chance it could remove too much wood!)

A sanding spindle chucked into an electric drill would do the job, too.

The important thing is to just attack it. Use what resources you can muster. It should not take too long to do this even with the slowest method, the humble sanding block. Coarse sandpaper can be your friend here.

Hope this helps

PGJ