Speech-bubble shelves hanging on the wall.

As we know, applying the clamping pressure at a right angle to the surface and in the center of the joint is the key to getting a tight and long-lasting joint. However, some glue-ups involve odd angles or irregular shapes that make exerting pressure on the joint at 90° using regular clamps extremely difficult, if not impossible. Such was the case with a pair of speech-bubble shelves I built that featured hand-cut dovetails and angled joinery.

Using examples as well as mock-ups, I will cover various clamping techniques for more taxing glue-ups grouped into three categories based on how the cauls for them are made.

These shelves’ rounded dovetails and acute angles raise the clamping challenge a notch higher.

Using a handscrew as a caul for a panel-repair job.

Clamps as Cauls

Handscrews provide for different closing angles and mark-free clamping in unusual positions. I use them as cauls when a regular clamp’s jaws may damage the object or its delicate edge through direct pressure. An example is when you need to clamp a round or half-round top panel together to fix a split top. The handscrew distributes the pressure on the panel itself, while the bar clamp pulls the top together without bruising its edge.

In a panel repair job such as this, the handscrew is used as a caul rather than as a clamp.

Using a cushioned hose clamp to distribute clamping pressure evenly and hold splintered bits together.

Another type of clamp caul is the hose clamp, which can work both as a clamp and caul at the same time. American antique furniture restorer Thomas Johnson cleverly uses a hose clamp with cushion material to hold broken leg parts together as one piece. The tightened hose clamp exerts pressure around the glue joint, while a foam strip placed inside the clamp protects the wood.

A cushioned hose clamp distributes the clamping pressure evenly while holding the splintered bits together.

Image left: Shop-made version of the Gyrojaw. Image midde: Using shims to position mating pieces roughly to the centerline of the Gyrojaw. Image right: Using the Gyrojaw as a clamping caul.

Lastly, clamping pieces with odd angles, such as clamping two tapered pieces together, can be quite a challenge. I have a secret angled caul to address that: a Gyrojaw. Working like an articulating vise face, the Gyrojaw allows the clamp jaws to exert pressure at 90° to the mating surfaces of the two tapered pieces.

Left: For clamping larger pieces, you can fabricate a shop-made version of the Gyrojaw from a scrap block.

Middle: Use shims to position the mating pieces roughly to the centerline of the Gyrojaw.

Right: The Gyrojaw earns its keep as a versatile caul.

Image left: CA glue provides a strong bond. Image right: Holding offcuts in position using strong double-faced tape.

Offcuts or Wedges as Cauls

For angled joints such as the ones in the speech-bubble shelves, I use their angled offcuts as clamping cauls. I used the same technique in the clamping of a compound angle basket. I have saved a bucket of scrap wedges cut at various angles for such jobs.

Left: A couple drops of CA glue provide a strong bond that can be undone with a quick smack of a hammer.

Right: Strong double-faced tape is another way to hold the offcuts in position.

Using styrofoam to protect moulding from clamps’ jaws.

Custom Cauls

Custom cauls are those that try to match the profile of the workpiece to apply the clamping pressure evenly. Two examples are shared here.

Soft but rigid materials are good candidates for making custom cauls. Styrofoam is a good example. Attach the Styrofoam to a board with double-faced tape and the stack becomes a rigid caul, which can be used to hold, as an illustration, a moulding in place.

Styrofoam protects the moulding from the clamps’ jaws.

Image left: An irregularly shaped table leg. Image right: Pressing the gauge’s pin teeth against the surface.

Soft wood can be used to make mirror-image cauls, too. All you need is a contour gauge and a pencil. First, locate the profile you want to copy, and use the contour gauge to record the shape.

Left: Curved or irregular shapes call for the use of custom cauls.

Right: Press the gauge’s pin teeth against the surface to obtain an exact copy of the contour.

Image left: Tracing the profile on a block. Image right: A custom caul.

Transfer the profile to a scrap block, cut it out, and now you have a perfectly shaped caul.

Left: Trace the profile on a block and cut it out on the bandsaw.

Right: The custom caul provides clamping pressure at a right-angle to the joint.

A project clamped with custom cauls.

Techniques such as these are valuable for clamping unusual glue-ups, and also valuable for furniture repairs or for fixing my project mistakes! “You can never have enough clamps” is a feeling shared by many woodworkers. Perhaps, “And you can never have enough cauls” could be added as a footnote to the favorite saying.

Text and photos by Charles Mak

Charles Mak, now in retirement, is an enthusiastic hobby woodworker, teacher, writer and tipster. He formerly worked part-time at his local Lee Valley Tools store.

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