I've received advice here to the effect that I should stain, then
assemble, then topcoat.
I've been making test pieces, as is my habit, and I like the results. My
aim is to come up with a finishing regimen that I can complete in a
reasonable amount of time on what is the better part of five sheets of
plywood (to say nothing of the face frame). But the method I used was
three coats of MinWax gloss poly cut (roughly) 50% with mineral spirits,
then rub down with 0000 steel wool and brown paper.
The finish looks and feels quite nice, even though I was pretty
haphazard in the application. But I can't easily imagine rubbing down
the bookcase surfaces effectively *after*
they are assembled, especially
in the numerous corners.
So I'll ask again: what is the downside to finishing everything before
assembly? I can think of two:
1. I have to mask the ends of each horizontal member, which will be a
pain, and unless I'm real careful, the dadoes in the uprights also. And
I'll have to mask "stripes" in the backs of the units, where the back
will be glued to the backs of the shelves. Of course, I'll have to do
all those things for the stain step in any case.
2. I may damage the finish in assembly.
So what are my options? I could decide to forgo the rubbing down and
live with a lesser degree of smoothness on the inside surfaces, which
make up practically the whole project (only the outsides of two of the
uprights will ever be seen). But having seen how good the results can
be, that would be disappointing.
[warning: high ignorance content]
Could I screw the backs on temporarily while I glue up the rest (to help
keep everything square), then remove the backs to allow for easier
application? That still leaves the steel-wooling and brown paper to do
inside shelf spaces that are as close as 11" apart. Would some kind of
orbital buffer be of any use? (the kind they sell for cars) Or might I
get a smooth enough finish (at least for the inside surfaces) if I tent
the whole thing to keep the dust out?
Or just perhaps, should I go the way I'm already leaning: prefinishing