Squaring Secrets for Glue-ups

Quick! You have just a few minutes to assemble the project parts, align the edges, and clamp the joints tight. Oh, and by the way, did you happen to get it square? With the right tools and these helpful hints, your glue-ups will be panic-free and perfect-fitting every time.

A precise glue-up begins with square parts, so make sure your tools (tablesaw, jointer, planer, mitersaw) are properly aligned before you machine parts. Then organize the glue-up on a flat, dust-free surface and use one or more of these clamping aids and techniques for squaring success. 

One part squares another

If you machine your parts square to begin with, they’ll square each other when clamped correctly. In the example shown above, square-cut shoulders on the rails align them perfectly perpendicular to the stiles. The trick here: Make sure the clamp pads sit squarely on the part edges. Applying pressure at an angle can torque parts out of square.

Here’s another way to make a glue-up self-squaring: Capture a plywood back or bottom snugly within grooves or rabbets to keep the box or drawer in shape, photo below.

Need a looser-fitting bottom to account for seasonal wood movement?

Make a squaring jig sized to fit snugly within a box opening, photo below, notching each corner to avoid glue squeeze-out.

For box joints, where the fingers stand proud during glue-up, use spacers or cauls, as shown in photo above, to keep clamp pads off the joints. The same technique also works for clamping the proud ends of dovetails.

Brace yourself

To keep simple butt joints square and in perfect alignment, a metal clamping square, photo above, holds project parts at a right angle while keeping one part from sliding past the mating part. Or if shop-built’s more your thing, make your own right-angle clamping jigs, photo below, to any size you desire. (See More Resources.)

Quick Tip: No braces? You can still prevent butt joints from sliding out of alignment. First apply glue to the end of one part; then rub the end against the second part to spread the glue. Separate the joint for about 10 seconds to let the glue surfaces become tacky and rub the parts together again. The added tack helps hold parts in place as you clamp. 

Other shop-made squaring solutions include custom-sized, notched clamping cauls that hold parts in position at the same time they distribute clamping pressure, photo below. Also, V-notched corner blocks help pinch parts together at mitered corners.

Certain clamps have built-in advantages for square clamping. A band clamp with four 90° corners, photo above, or a four-way frame clamp, photo below, for example, help square all four corners of a glue-up at once.

SHOP TIP

A no-measure diagonal double-check
Even if you don’t own a reliable square, you can still check for square by measuring between opposite corners on a project. If the diagonals measure the same—and the opposing sides are equal length—you know it’s square. If clamps interfere with this measurement, or you’re gluing up several identical assemblies, try this simple alternative. Cut two scrap strips, each a few inches longer than half the length of the diagonals. Then cut one tip of each strip to about a 30° angle. Hold the strips together with the angled ends in opposite corners and clamp them together. Using this as your gauge, measure the other diagonal to confirm a square glue-up. To equalize the distances, lightly clamp across the diagonal corners that are farther apart.

Sources

Band clamp: Merle Adjustable Clamp no. 9012, MLCS, 800-533-9298, mlcswoodworking.com.
Four-way frame clamp: Veritas clamp no. 05F01.01, Lee Valley Tools, 800-871-8158, leevalley.com.
Clamping squares: Pinnacle square no. 147530, Woodcraft, 800-225-1153, woodcraft.com.

MORE SOURCES

FREE PLAN
■ “Right-Angle Clamp Jig”
woodmagazine.com/brace

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■ “Fine-Furniture Accuracy from Any Tablesaw”
issue 187 (November 2008)
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