alt Hacker NewsI'm not even thinking about that kind of precision work.
For a basic bookshelf, the space might be constrained. Say I need the outside dimension to be 24.5" wide. If I'm using 3/4" plywood, do I model it so I have 23" wide shelves or 23-1/16" wide shelves?
Or is it irrelevant? Do you build the box first, then measure and cut the shelves to fit?
The more I think about it, the more I'm concluding that you use 23/32" and then do a lot of measuring and adjusting as you build. Taking a cut list and cutting everything ahead of time is probably a bad idea unless you know your plywood is exactly the right thickness.
In most applications, it doesn't matter if the piece ends up 1/16" (1.5mm for the rest of the world[0]) undersized and I wouldn't worry about it. If for some reason the finished piece had to be 24.5" wide, I'd account for the off-nominal thickness of the plywood and charge more for the hassle of it :-)
Generally though, if you're putting something into an alcove and want a fitted look, you'd build the box undersized by some amount (1/4" to 1/2" depending on how square and plumb the walls of the alcove are), set the box in place, and then scribe a face frame to the walls.
Drawer boxes tend to be where you have to work to the tightest tolances. Side mount drawer slides don't have a lot of allowance for the drawer to be undersized and basically none for it to be oversized. Under mount slides are a little more forgiving, but I definitely still account for my actual material thickness on them. In either case, you're definitely building the drawer boxes to the as-built size of the opening they're going into and not the platonic ideal opening from the plans/drawings.
[0] Yes, I know. Slightly more than that, but this is woodworking tolerances.