Discover Jim Probst’s Four-step Process for Seamless Panels.
For many beginning woodworkers, one of the most intimidating aspects of solid wood furniture construction is gluing up wide flat panels for large project parts. That’s because, unlike other jobs, slow and steady won’t win this race. Once you spread the glue, you have less than 10 minutes to pull everything together.
Professional woodworkers like Jim Probst (see “Traditional Cherry Wardrobe”) rely on a step-by-step routine to ensure that glue-ups go glitch-free. Blend his techniques with your own, and your glue-ups are guaranteed to go faster and easier.
Step 1: Go for Good Looks
Too often, woodworkers get so involved with the mechanics of a glue-up that they forget about the most important end result−aesthetics. Few things look worse than poor grain matches. If possible, buy boards that come from the same log and are long enough to get at least two top pieces from each. Allow about 30% extra for waste. Here are some other tips to help you work with stock you have on hand.
If your boards are rough-cut, and you can’t make out the grain patterns, skim the surfaces on your jointer or with a hand plane. If you can afford to lose some width, rip off any sapwood or other blemishes. (Sometimes you can “hide” sapwood by putting it on the underside of your top.)
Lay the boards edge to edge and then slide each board back and forth, or rearrange the order, until the grain patterns blend harmoniously. (See the opposite page, bottom right). Once the boards are arranged to your liking, cut them to rough length–about 2” longer than needed. The extra length gives you the freedom to slide the boards slightly during glue-up. (Later, after assembly, you’ll trim the panel to size.) Surface and thickness-plane your boards about 1⁄16” thicker than the finished dimension.
You’re ready to joint the edges and test-fit your top. Rather than aim for a dead-straight edge, plane a tiny dip in the center of each board. (When the boards are placed edge to edge, a hint of light should peek from the middle of the joint.) This “sprung joint” helps compensate for future moisture loss at the panel’s outer edges. If gaps exist at the outer edges of the joints, it’s almost certain that they will open up regardless of the glue strength.
After jointing the mating edges, lay your boards out again and check the pattern. Once satisfied, mark a V across the faces with a pencil or chalk to correctly reposition them later. Leave an extra 1⁄4” on the outermost edges to protect the panel from dents and dings. After assembly, you’ll trim the panel to final width.
Panel-Making Myths
Occasionally, a myth is repeated so many times that it becomes accepted as fact. Here are some common myths about glue-ups.
Myth 1: Alternating the growth rings on flat-sawn stock is the best way to minimize cupping.
Fact: Matching for looks is more important. (In fact, some cabinetmakers prefer orienting boards so that the center of the tree faces up because the “inside face” has a richer appearance.) As long as the top is properly attached to a base, movement isn’t an issue.
Myth 2: For a really strong edge joint, you need to use dowels or biscuits.
Fact: Not true. Dowels and biscuits can cause more problems than they solve. Dowels do not expand and contract along with the rest of a top and can actually force a good joint apart. Biscuits swell enough to make raised areas along a glue line. Also, if a panel is sanded too soon after glue-up, when the moisture from the glue in the biscuit pocket finally evaporates, you may end up with depressions on the surface where each biscuit is located. Realize that with a good joint and fresh glue, a simple edge joint is stronger than the surrounding wood. The only time you might consider using biscuits is if your boards are slightly bowed. In these situations, the biscuits need not be glued and only serve as alignment aids.
Myth 3: Too much clamping pressure will “starve” a glue joint.
Fact: There is some truth to this but the fact is, most woodworking clamps are not capable of exerting too much clamping pressure. Bar clamps and pipe clamps apply the most pressure of commonly available clamps. If you snug them up firmly, you should be just fine. More important is to use enough clamps for the job. Clamping force radiates out 45° from the clamp head, so you want to space the clamps in such a way that you end up with even pressure along the entire glue joint.
Step 2: Get Ready to Glue
Now’s the time to gather your clamps and other supplies. There’s nothing worse than being in the middle of a glue-up and having to search for something you forgot. First you need a flat surface to work. If this is your workbench, you may want to cover it with cardboard or kraft paper.
Now pull out your clamps. You’ll need at least five clamps for a panel over 4’ long. You should have a couple extra clamps at the ready to help flatten your panel, if necessary. You should also use clamp pads to spread out the pressure and prevent the clamps from marring your work. A nifty solution is to make clamp pads that stay on the clamps using scrap plywood about 4 × 4”
with a 11⁄4” hole in the center. Additionally, you’ll also want to have a few C-clamps, a straightedge, and a dead-blow hammer. Don’t forget the glue. Regular yellow glue works fine for panel glue-ups. Use a disposable plastic knife for a spreader.
You’re almost ready to glue. Prearrange the first three clamps on your bench. Center one clamp in the middle of your assembly bench, and position the other two about 6” in from the ends of your boards. Take a minute to adjust the clamping heads so that you’ll only need to tighten them once you’ve applied the glue.
Tip Alert
Yellow glue normally has a five-minute open time. Titebond Extend has a 15-minute open time that helps when tackling complex glue-ups.
Step 3: Glue and Clamp
Once glue is applied, you have about 5 to 10 minutes to accomplish your task, and there’s no turning back. The best way to prevent panic is with preparation. Do a dry run.
A no-glue clamp up is the best way to check for any glitches you might encounter. Don’t apply heavy clamp pressure on a dry run. Do just enough to see if you have any issues with the seams closing completely. If necessary, you may need to re-joint an edge or two. Unclamp the assembly.
Stand your boards on edge and apply a bead of glue on each mating surface. Then spread the bead out evenly. The amount of glue you use is a judgment call. You want enough glue to get nice even squeeze-out. If there is no ooze, you haven’t applied enough. If glue is dripping everywhere, you’ve applied too much.
Next, pull everything together. Lay your boards down, and match up your pencil lines. Tighten the center clamp until the glue begins to ooze; then lightly tighten the end clamps. Now, starting at the center of your panel, align each joint as closely as possible, as shown in Photo A. Sometimes the joints need some persuasion from a dead-blow hammer to fall in line. Use C-clamps at the ends of the panels to make them even, as shown in Photo A Inset.
The problem with the bottom-clamp only arrangement is that the panel is likely to cup. To counteract this tendency, you want to add clamping pressure across the top of the panel. Using your straightedge, check the flatness of the panel as you go, as shown in Photo B. Sometimes, you may need to use extra
clamps to pull the assembly flat (Photo C). Once all is as it should be, tighten each clamp and then do one final flatness check before you take a break and let the glue dry.
Tip Alert
To prevent the black stains that can occur when metal clamps come in contact with glue and wood, you might want to run a strip of masking tape down the length of your clamps. Conquer the challenges of wide flat panel construction with a proven routine that makes glue-up glitch-free and a lot faster.
Use finger pressure or a light tap from a dead-blow hammer to align the edges of the boards. A C-clamp can help flush up joints at the outmost ends of the panel (inset).
Balance the clamping pressure on both sides of the panel. With equal clamping pressure, you should see an even bead of squeeze-out along the joints. Use a straightedge to check for flatness.
It’s handy to have an extra clamp. Using one more clamp along the top persuades the panel to bow away from the bar and flatten itself out.
Step 4: Cleanup
After an hour, the glue will be at 80% strength, but the squeeze-out should still be gel-like. At this point you can remove the clamps and begin the cleanup. First, use a hook-type scraper, as shown in Photo D, which will do a fine job of removing the partially cured glue. If you encounter tear-out, try scraping from the opposite direction. When done, wipe the surface with mineral spirits to highlight any missed spots.
After scraping off the glue, give the panel at least 24 hours to dry. This might seem excessive, but the extra time allows the wood alongside the joint to release the moisture it absorbed from the glue. If you smooth the panel too soon, the swollen wood around the glue line will dry and shrink, resulting in a visible dip.
Once the panel is dry, knock down any out-of-level joints. To do this, use a #4 bench plane, as shown in Photo E, to smooth out the entire panel. Since a little tear-out is inevitable, finish up with a card scraper, as shown in the opening photo.
To avoid the risk of rounded-over edges, don’t trim the panel to final dimensions until you are done sanding both sides through 180 grit. After trimming to size, a final hand-sanding with 220 grit is all that’s needed before applying your stain or finish.
Tip Alert
If you have an unusually large top, glue the boards one-by-one. There’s nothing wrong with doing glue-ups in stages.
After the glue congeals and it’s safe to remove the clamps, use a scraper to clean up the joints.
Working diagonally across the panel, use a #4 bench plane to quickly level the boards, or go with a belt-sander for similar results.
