How to Clamp

Meet the pro

In 30 years as a professional woodworker, Dave Munkittrick has tried just about every clamping technique imaginable. Some of them are his own inventions; some are borrowed from other woodworkers. As for the rest, he’s been doing them for so long that he can’t remember where they came from.

Dave says, “Over the decades, I have amassed a huge collection of clamps—every size and type. But the arsenal of clamps in my shop is no more valuable than the arsenal of clamping tricks I carry around in my head. So even if you’re a beginning woodworker with a modest clamp collection, these tips are for you. I’ll show you how to clamp to get the most from the clamps you have and even a few ways to clamp without clamps.”

Cauls keep glue-ups flat and flush

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Cauls prevent bowing

Cauls made from 2x4s clamp the faces of edge-glued boards to keep them flat. Arrows indicate the direction of a slight bow in each caul.

As you squeeze boards together with pipe clamps, they sometimes arch or slip out of alignment. Pairs of upper and lower cauls are the solution. I lightly squeeze the cauls with bar clamps, then tighten the pipe clamps, then tighten the cauls a bit more… I continue this back-and-forth process until the boards are joined flush and flat.

My favorite cauls are made from 2x4s. I carefully select ones that have a slight bend or “crown” along the 1-1/2-in. edge, but no twist or warp. The crown is an advantage because it creates extra pressure in the middle of the caul. I label all my cauls with an arrow marking the direction of the crown and the length of the caul.

What’s a caul?
If it’s designed to spread clamping pressure over a wide area, you can call it a caul.

Prevent clamp stains with wax paper

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Wax paper barrier

A strip of wax paper separates the clamps and the wood surface and prevents stains.

Moisture in glue triggers a reaction between iron and chemicals in wood (called “tannins”). The result is black stains on the wood, especially with tannin-rich woods like oak or walnut. A strip of wax paper acts as a barrier between the clamp and the wood. I also use wax paper to keep glue off my cauls.

Apply pressure with water

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Water bucket weights

Buckets of water are heavy and spread clamping weight evenly over a wide area.

Some woodworkers keep a stack of bricks in the shop for those times when weight is better than clamps. But I think plastic buckets make the best weights. Filled with water, they provide a lot of weight. When empty, they’re light, easy to store and handy for other jobs.

Give clamps a lift

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Clamp jacks

Make your own handy clamp jacks from scraps of 1/2-in. plywood.

Homemade clamp jacks raise your pipe clamps off the bench so the handles turn freely and there’s plenty of room underneath for alignment cauls and clamps. The jacks also act as pads to keep clamps from denting the wood. My jacks are 8 in. tall and made from 1/2-in. plywood.

Shift clamps to square your work

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Squaring a face frame

Slightly shift one or two clamps and tighten to draw the face frame into a perfect right angle.

To check the squareness of a cabinet frame or box, take diagonal measurements. If the measurements aren’t equal, shift the positions of the clamps. In this photo, I exaggerated the shift for clarity. In most cases, a slight shift will do the trick. Sometimes, shifting just one clamp will pull the assembly into square.

Use one caul instead of many clamps

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Gluing a thin edging

A caul spreads the clamping pressure more evenly over the thin edging.

Thin, flexible parts require lots of clamps to create a consistently tight fit. Or you can use a caul. This solid-wood edging on plywood, for example, would have required a clamp every few inches. But with a stiff caul to spread the clamping force, I was able to use fewer clamps, spaced far apart.

Iron out veneer-clamping problems

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Anchoring veneer

A hot iron activates a thin coat of dried wood glue to "clamp" the veneer.

Gluing down veneer is tough. You have to apply flat, even pressure over every square inch. There are fancy tools for this, but for small veneer jobs, try this nifty trick: Apply a thin coat of wood glue to the substrate and the back of your veneer. Let the glue dry. Then position the veneer and use a hot iron (no steam) to reactivate the glue and press it into place. The bond is almost instant and very strong. I love it.

Overhead hold-down

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Overhead clamp

Not fancy, but this 2x4 clamp from above is effective.

Sometimes, a 2x4 wedged against overhead joists is better than a clamp. When routing a tabletop, for example, I can rout all the way around without stopping and shifting clamps. This trick is also handy when I need to apply pressure where clamps won’t reach: gluing down bubbled veneer in the middle of a large tabletop, for example.

Hold it square

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Corner blocks

Clamp L-shaped corner blocks to the sides to square-up box corners.

When you’re clamping cabinets together, getting a square assembly is half the battle. These simple blocks, made from three layers of 1/2-in. plywood, pull the cabinet into square and keep it there. After the squaring blocks are in place, I use pipe clamps to squeeze the joints tightly together.

Long-jaw hand screw

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Extended hand screw

Lengthen hand screw jaws with scrap wood.

Extend the reach of your hand screw clamps with a couple of lengths of scrap wood. Screw the jaw extensions to the side of your hand screw and away you go. Works great and couldn’t be easier.

Magnetic clamp pads

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Easy-stick clamp pads

Magnets mounted in small wood blocks hold the pads on the steel clamp jaws.

Instant on and instant off. You can’t beat the convenience of these wooden clamp pads. Best of all, they don’t leave oily stains like the plastic ones do. To make mine, I drilled shallow holes in 3/8-in.-thick blocks of softwood. Then I dropped in dabs of epoxy and inserted rare earth magnets. My magnets were 1/2 in. diameter and 1/8 in. thick. Make sure the magnet is flush or slightly below the pad surface.

How to clamp with tape

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Tape clamp

Clamp odd-shaped objects with flexible electrical tape.

Every woodworker I know occasionally uses masking tape in place of clamps. But I prefer electrical tape because it’s stretchy and lets me put the pressure exactly where I need it.

Slow down!

Glue-ups can be a frenzied, nerve-jangling activity. So why not slow things down a bit? Take the edge off your glue-ups with a slow-setting glue such as Titebond’s Extend. The extra 10 minutes of open time can be a real lifesaver and nerve calmer.

Anti-slip tip

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Pinning a glue joint

Anchor a glue joint to keep it from slipping with a few almost-invisible pin nails or brads.

Wet glue is like grease, allowing parts to slide around while you’re trying to clamp them. But a few strategically placed brads or pins prevent that frustration. I like to use my 23-gauge pinner because the heads are almost invisible. But a standard brad nailer works too.

Convertible pipe clamps

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Joining pipes

You can easily lengthen pipe clamps with nipples and additional lengths of pipe.

When you buy pipe for your pipe clamps, also pick up some couplers. That way, you can join pipes to make longer clamps.

A dry run is a must-do

Every time I skip this step, I end up regretting my impatience. Don’t make the same mistake. Take the time to rehearse your glue-up. That way you’ll know all the clamps you need are at hand and there won’t be any nasty, unexpected misfits in your joinery to ruin your glue-up and your day.

Put the pinch on miter joints

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Corner clamping

Make special clamping blocks to tighten miter joints.

A pair of notched “pinch blocks” puts clamp pressure right on the miter joint. This approach is especially good for picture frames because it lets you deal with one joint at a time rather than all four at once. Position the blocks shy of the mitered ends so you can see how the joint lines up.

The most useful clamps

Essential Clamps for Beginning Woodworkers (and Everyone Else)

Pipe clamps: Pipe clamps are the everyday, high-pressure workhorses of woodworking. They cost about $15 per set, plus a few more bucks for pipes. Because you can quickly screw the clamps onto different lengths of pipe, one set of pipe clamps does the same work as several lengths of bar clamps. Buy pipes in 2-, 3- and 4-ft. lengths and you’re ready for most situations.

Bar clamps: Quicker and easier to use than pipe clamps, light-duty bar clamps are perfect when you need a long reach and moderate pressure. They cost about $8 and up depending on length.

Spring clamps: These are the fastest helpers for holding your work in place or doing light-pressure clamping. They’re cheap, too: Most cost less than $5.