Fixing the piece that doesn't quite line up
Okay. So you clamped everything up last time, no glue, just checking the fit. And for some of you, it lined up fine. Corners tight, everything sitting flush, and you're probably feeling pretty good about yourself right now.
For the rest of you, something's off. A gap where two pieces meet. A shelf that rocks a little when you set it on the bench. A side piece that leans instead of standing straight up.
Good. I mean that. This is exactly the lesson you need.
First, figure out what kind of problem you have
There are basically three things that go wrong at this stage, and they each get fixed differently.
The gap problem. One edge isn't sitting flush against the other. Usually this is a cut that wasn't quite square, which we talked about a couple lessons back when we checked cuts against the square. If you skipped past that check because your cut "looked fine," this is where it catches up with you.
The rock problem. The shelf doesn't sit flat. Usually one leg or one side is a hair longer than the other, or your bottom shelf isn't parallel to your top shelf. This one's sneaky because it doesn't show up until you've got the whole thing together.
The lean problem. Nothing is horizontal or vertical the way it should be. This is almost always a measuring issue from way back, and it's the hardest one to fix after the fact, so we'll spend the most time on it.
Finding out where the error actually is
Before you fix anything, you need to know exactly where the problem lives. Don't guess. Get down at eye level with the joint and look at it straight on. Use your square right on the joint itself, not just on the individual boards.
I feel like people want to skip this part because they already know something's wrong and they just want to fix it. But if you fix the wrong spot you'll have two problems instead of one.
Fixing a gap
If a gap is small, less than about a sixteenth of an inch, honestly, in this class, at this stage, I'm not going to make you re-cut anything. A little gap on a shelf is not the end of the world. It'll close up some when you clamp with glue, and if it doesn't fully close, that's a lesson for next time, not a crisis for this one.
If the gap is bigger than that, the pieces probably need to come apart, and one edge needs a fresh cut or a pass with a hand plane if you've got one. We haven't done planes in this class, so if you're in this spot, come find me and we'll sort it out together on your bench, not just from across the room.
Fixing a rock
Set the shelf down on the flattest surface in the room, which is usually the workbench, not the floor. Find out which corner or edge is high. A lot of the time it's not that one piece is wrong, it's that two pieces that are each fine don't agree with each other.
The fix here is almost always sanding down the high spot a little at a time, checking, sanding again. Slow. You are not trying to fix it in one pass. This is a place where going too fast will turn a small problem into a bigger one, because you can't put material back once it's gone.
Fixing a lean
This is the one where I want you to be honest with yourself about the reference edge thing we've talked about before. My opinion on this, and I'll say it again because it matters: measuring twice doesn't help if you measured from two different starting points both times. All your errors need to trace back to one edge, one reference, every time. If a piece is leaning, nine times out of ten it's because somewhere in the cutting or the layout, the reference point shifted.
Sometimes the honest fix is a new piece. I know that's not what you want to hear after all the work you put into cutting these. But a shelf you understand is more useful to you than a shelf built out of pieces you're fighting with the whole way through.
A word on patience here
This is normally where I slow the whole class down, and I know that's frustrating if you're ready to move on to glue. I'd rather you leave today with a shelf that sits flat and square than a shelf that's fast but wrong. That's just how I teach. If it's making you crazy, tell me, but I'm probably still going to make you check it twice.
My neighbor Rodney came over once just to borrow a drill, and three hours later we'd built a birdhouse neither of us needed, mostly because the first two walls didn't line up and we kept taking it apart and doing it again until it did. Neither of us was in a hurry that day. That birdhouse is still hanging in his yard. Not great, but it held, and it's square, which is more than I can say for some of my early stuff.
Before next time
Get your dry fit sitting flat, square, and gap-free before you leave today, even if it takes a few passes. Next time we glue it up for real, and there's no fixing a lean once the glue sets.