Gluing up is unique among woodworking operations in that it is time-sensitive and irreversible. No doubt that explains the accompanying tension and the frequent unhappy results — Ian Kirby
We've gathered some tricks and tips that will help woodworkers, from experts to novices. Click through to find clamping techniques that will enlighten your shop experience.
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Even the common C-clamp is being upgraded and revamped for woodworkers.
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The variety of clamps available to the woodworker is expanding all the time. New features and accessories all make the process of clamping easier. But the most important fundamental steps to successful clamp-ups are well-formed and -fitted glue joints, a complete test run (dry test) of the clamp-up (ever more important as the subassemblies become more complex) and an appropriate glue or adhesive for the task at hand.
Starve a Joint — Feed a Failure
A simple but critical clamping point is the application of the glue. Too much, and you've got a big mess and the glue surfaces are likely to slip and slide into misalignment. Too little, and the joint is prone to failure. If you apply too much pressure to the clamp-up, the results will be the same as if you failed to apply sufficient glue to the joint ... the glue will squeeze out of the joint and it will effectively be "starved."
The Fan Effect
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Fans of pressure extend from each clamp head until they reach the glue joint. In the example above, the fans overlap more than they would need to, but clearly, a single clamp would not have applied pressure along the entire length of the joint.
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When you're edge gluing, the pressure generated from each side of the head of a clamp spreads out at 45° until it encounters the glue joint. As you can see in the photo (at right), these fans of pressure will determine how many clamps are required for an effective glue-up. In the example, one clamp would not have been enough, but the three pressure fans generated overlap to a degree that's a bit excessive. Also demonstrated in the photo is the practice of alternating clamps on opposite faces of the panel. This helps to keep the panel flat, but you need to check the glue-up with a straightedge of some sort to be confident that the boards are correctly aligned.
Clamping blocks are another way to control your glue-up. The blocks allow you to place the clamping pressure exactly where you want it to close the joint and keep the panel flat. (See photo, below) You determine where the blocks must be placed during your dry clamp test. (Glue blocks also protect the edge of your panel from metal clamp heads, but that's a side benefit.)
Tongue-and-groove Joints
Tongue-and-groove joints add another wrinkle to the clamping game. Not only do you need to apply pressure to the edge of the panel to draw the joint together, but it's best if you can squeeze the joint together onto the tongue. Again, clamping blocks come to the rescue.
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Use clamping blocks and a C-clamp (positioned as shown in the photo at left) to squeeze a tongue- and- groove joint tight (photo at right).
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Dry-bent laminations are an advanced gluing technique that can be exceptionally useful.
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"Dry-bent" Laminations
The technique for creating curved shapes — for elements like table skirts or chair legs — is called dry-bent laminating. It is very simple in concept. Create a form matching the shape you desire. (These forms can get quite large.) Use very thin strips of wood — thin enough that they bend very easily — and, as always, test clamp them in your form. After the dry test, apply a thin coat of glue to each strip of wood, and clamp them tightly in the form. It's a good idea to wax the clamping faces of the form. When the glue dries (and it will take several hours to cure), the glued-up strips will retain their curved shape. In addition, the product you have created will be very strong, as a result of the multiple laminations.
Accuracy When Gluing Up
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There are three simple keys to accurate and effective gluing and clamping: preparation, preparation and preparation. Click to Enlarge
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Because the result of gluing and clamping a subassembly together is more or less permanent, it is essential that once your clamps are set you verify that all the pieces are square, flat and properly aligned. Measure across the diagonal of any square or rectangular aspect of your piece ... the measurements should be exactly the same. Use a straightedge to check that the subassembly is flat. A good set of winding sticks is a practical way to make sure your subassembly is not twisted in any way. You only have one chance to get it just right ... take your time and be sure all is well.