Clamp down on glue-up mistakes
Gluing up and clamping a project proves just as critical as the machining and finishing stages, so take the time to get it right. These tips will save you time, grief, and, quite possibly, your project.
A dry-fit solves problems
It's tough to solve fitting dilemmas while your glue bonds with the wood, and there's no going back after it has set. To keep yourself out of that bind, always dry-fit your assembly--that means no glue-to verify all joints fit together as planned, as shown in photo. If joints don't fit, go back and solve problems before applying glue.
Dry-fitting shows which clamps and how many are needed, and where on the assembly they go. You also get an idea of how long it will take to glue and clamp the assembly--you might discover that the process takes longer than the glue's open time allows (typically less than 15 minutes for yellow glue). In that case, divide the work into sub-assemblies. For example, when building an end table, make two assemblies of two legs with their rails and let them dry, rather than trying to assemble all four legs and rails at the same time.
Mask hard-to-get-at spots
You also can save yourself time and worry during a glue-up with some prep work during the dry-fit. Rather than trying to remove messy glue squeeze-out in hard-to-reach places after you've put the clamps on, take this time to mask those troublesome spots, such as the inside corners of a chest or case, as shown in the photo, with painter's tape. Wipe off glue squeeze-out while it's wet.
Flat panels start on a flat bench
Edge-glued panels make up a big part of many large furniture projects, so you want them to turn out perfect. To avoid panels that warp or require great work to flatten them, work on a flat surface or benchtop. Assembling a panel on a warped surface can transfer that warp onto your glue-up.
Clamps on joints keep boards flush
Add clamps over gluelines along the ends to keep the board faces flush.
Matching clamps can mean equal pressure
Use similar clamps. Mixing clamps in a specific application can cause differences in clamping force and lead to warping. The photo shows matching aluminum bar clamps to pull the boards together edge to edge. It's okay to use hand clamps on the ends because they apply clamping force in a different direction than the bar clamps.
A simple balancing act
Alternate clamps over and under a panel or long glue-up to balance the clamping pressure.
Tighten each clamp slowly
Snug up and tighten clamps evenly. Add a little pressure to each clamp in sequence rather than tightening each one fully before moving on to the next clamp.
Avoid excessive pressure
Don't overtighten your clamps. Too much force can cause a panel to cup, as well as squeeze out too much glue. Apply only a thin film of glue to the wood surfaces (excess glue will just squeeze out and require cleanup); then use just enough clamping force to produce glue squeeze-out that forms a uniform thin line or beads along the glue line.
Center your clamping pressure
Align the center of the workpieces being clamped with the center of the clamping force, in this case, the screw on the pipe clamps. This places your glue joint directly in line with the clamp's greatest pressure. Use scrap stock to elevate the assembly to the screw height.
Let it sit
Finally, leave a clamped assembly on your flat table or workbench for 30 minutes before moving it. This gives the glue time to bond with the wood. Moving it right away or leaning it against a wall or cabinet could cause warping.