A few weeks back I promised a panel glue-up primer… and today is the first time I’ve needed to glue up a panel since. The basic stock prep for the panel pieces is the same as the rest of the prep, until it comes to sticking the two (or more) pieces together. So that’s where I’ll pick up. And as always, it’s best if you can surface your lumber then do any glue-ups within a few hours. The less time the wood has to move, the better – even if you’ve properly acclimated it.
If I’m using yellow glue or liquid-hide glue (which is almost all the time), I rip both edges of pieces for a glue-up; I want those outside edges flat and level so the clamps have a good, parallel surface on which to close. If I’m using hot hide glue and doing a rub joint (which is almost never), there are no clamps involved, so the outside edges don’t matter.
Regardless of my approach, the first steps are the same. Lay out the panel and mark it with a cabinetmaker’s triangle.
You want to joint the edges so that you cancel out any non-perfect-90° angle from your electric jointer or jointer-plane work. If you’re jointing by hand, match-plane the two while clamped together in your vise. This will cancel out any error in your angle. If using a electric jointer, mark one edge “I” (inside) and the other “O” (outside). I runs against the fence, O runs not against the fence. This cancels out any error in the jointer’s fence.
I carefully joint each mating edge, fairly slowly, and at the same, steady speed. Then I immediately proceed to glue up.
Let’s dispense with the rub joint first. For a panel glue-up, the only glue I’d use for a rub joint is hot hide glue (though some sources will say other glues work, too). With the two mating edges freshly jointed, simply coat both edges – quickly – then rub those two edges together lengthwise until the glue starts to gel, doing your best to keep them aligned across the thickness. Then set them on end against a wall and give the glue time to completely dry. No clamp necessary. (The few times I’ve glued up panels this way, I’ve left them a little thick so that I can level the glue line after, and not end up with a too-thin panel. Typically, I use the tack-ability of hot hide glue only for glue blocks and veneer.)
I use liquid hide glue (preferably the the Old Brown stuff) for most things in woodworking, but for typical panel glue-ups, I reach for the yellow stuff. It sets up more quickly, so the clamps can come off after 30 minutes (which means I can get more glue-ups done more quickly – and every minute is precious when prepping stock for classes).
I’ll have a glue-up station ready to go on my bench before I bring stock in from the machine room, usually with a piece of paper underneath an odd number of clamps, because I always want one in the center (and if my prep is good, I can dispense with putting every other clamp on top of the panel). Along with the glue bottle, I have a bucket of water (hot water if I’m using hide glue) and a rag.
First, I run a bead of glue down the center of one board.
Then I spread it evenly with my finger (which is fast) or with an old toothbrush (which is slower but less messy).
I want enough glue that I can rub the wet edge on the dry edge and get enough glue on the mating board that its edge is also fully wetted. But no more than that.
Then I wipe the excess glue off my finger before tightening the center clamp. I keep a finger or two of my non-clamp hand on the seam so that I can feel if I need to exert downward pressure on either board for a perfect mate. (Usually, doing the glue-ups immediately after prep obviates this problem.) I don’t tighten all the way – just enough to hold the joint closed as I repeat at both ends. Then I snug them in the same order until the joint is fully closed and I see a line of glue beads down the seam. That tells me the joint is closed tightly enough, and that I used enough (actually, just a tiny bit too much!) glue.
Next I reach for the bucket and rag, and with an almost-completely wrung-out rag, wipe off the excess glue with small circular motions along the seam. Rinse, re-wet and re-wring the rag often (you don’t want to simply spread thinned glue over the surface). And don’t forget to do the other side. You’ll have a little squeeze-out under the clamps, but it’s easy enough to knock off with a scraper, chisel or plane after the glue is completely dry. Note that none of us in this shop has ever had a problem with glue-size interfering with finishing. Any residual glue is planed away.
The last task is to check the clock and write the time on the edge of the panel. After 30 minutes, you can take the clamps off and move on to the next glue-up. With multiples, I usually stack them up to dry (another reason to remove the glue on the surface), and let them sit overnight before ripping to final size and squaring the ends.
I know there are all kinds of charts, studies and special clamping doodads to help you achieve ideal clamp pressure. I’m sure those are useful. For someone. Me? This simple approach has served me well for more than a decade.