Wood Clamps

Properly secure your glue joint with these tools.

Photo: Flickr

Wood is a remarkable material. It’s widely available, handsome, and immensely diverse. Many of its varieties can easily be cut, sculpted, bored, and otherwise shaped in a hundred different ways. Wood can be fastened to metal, plastic, or other pieces of wood, using nails or screws. But the most miraculous of its tricks, at least for me, is wood’s willingness to be clamped and glued.

A properly prepared glue joint (and this is the amazing part) is as strong as the sinews of the wood itself. I’ve seen many broken pieces of furniture that snapped and cracked not at a glue joint but as a result of flaws in the wood itself. Not every glue joint is perfect, of course, but those that are can endure for centuries.

The first key to a good joint is proper clamping. The clamp—most are devices with pairs of jaws that are drawn together with screw mechanisms—is responsible for pulling together the pieces to be glued, and for holding them tight and flush until the glue sets. The other key is the glue, and using the right kind in the right way. But first let’s talk about the array of clamps that are available.

Clamps (or, as they like to call them in England, cramps) are in­valuable tools in the workshop. But unlike the vice, another tool that can be used to hold workpieces together, clamps are easily portable, which makes them most con­venient problem solvers at the work-site. Here are a few clamps for which you may well find many applications.

C-Clamps. These multipurpose clamps get their name from their shape. Especially practical for gluing in tight spaces, these clamps have jaws in the shape of the letter C, and rely upon screwdrives with metal shoes at their ends to hold workpieces tightly. The screwdrive is driven by a T bar that forms a handle on the screw; in general, finger-tightening will provide adequate force. The shoe is mounted on a ball joint, allowing it to sit flush even to slightly angled stock.

C-damps are made of aluminum, iron, or steel, and are designed to clamp metalwork. When used with plastic or wood, pads are generally used to protect the material from telltale indentations that are left by the metal jaws and the shoe of the clamp when tightened. Clamps come in a range of sizes, with jaws as small as one inch and as large as twelve inches. Some have deeper throats than others, to accommodate clamping some distance from the edge of the workpiece.

Bar Clamps. The bar is the backbone of this clamp, a rectangular length of steel or aluminum. There is a jaw at one end of the bar, and a tail slide that moves up or down its length. The tail slide can be fixed in the desired position at one end of the workpiece that is to be clamped. Depending upon the design of the clamp, this is done using a peg that passes through the bar or by locating the slide at one of the notches in the bar. The adjustable jaw device, which uses a screwdrive, can then be tightened over the workpiece at the other end.

Bar clamps, which are also known as joiner’s clamps, are sold in two- to six-foot models. The steel clamps, in particular, can exert con­siderable force in clamping. Pipe clamps and bar clamps have strongjaws, and can be used in rough framing to pull a reluctant joist or header into place. More often, they’re used in cabinetwork or to repair doors or windows.

Pipe Clamps. At first glance, the pipe clamp resembles the bar clamp, save that the spine is in the form of a length of pipe. As with the bar clamp, the pipe clamp has a jaw that in most models is fixed to one end of the pipe. A second sliding jaw can be positioned anywhere on the length of the pipe, with a cam operated by a lever mechanism or a clutch that is engaged when an object is clamped in place.

The fittings for pipe clamps can be used on any length of pipe. Two sizes of fittings are common, designed for half-inch and three- quarter-inch iron pipe.

Hand-Screw Clamps. All-wood hand-screw clamps were the rule for generations. One great advantage of wooden hand-screw clamps is that, when used properly, they apply pressure evenly over a larger area than most clamps, meaning they are less likely to mar a workpiece than other clamps.

The wooden screws in the older models travel freely through one jaw and thread into the other; the front and rear screws are the reverse of one another. The newer, steel-screw models have threads at each of the points of connection with the jaws, but the thread on each rod reverses at its midpoint, for ease of adjustment. Both wooden and wood-and-steel designs can be loosened or tightened by gripping them with both hands, a handle in each hand, and rotating the clamp. A clockwise rotation tightens the clamp.

For most uses, the clamp should be tightened to fit the workpiece with the jaws roughly parallel. When the mouth of the clamp is snug over the workpiece, turn the rear handle to fully tighten the clamp. When gluing, take care to avoid gluing the wooden jaws to the workpiece.

Over the years, these clamps have been manufactured in a great range of sizes, and today clamps can be purchased with jaws that open up to a maximum of twelve inches or more. Typically, the hardwood jaws are between eight and eighteen inches long, and be­tween one and a half and two inches square.

Spring Clamps. These clamps mimic the shape and function of the human hand when you are grasping something between your thumb and forefingers. Only this clamp is quite happy to remain in place in­definitely, exerting uniform pressure, enabling you to go off and do something more interesting.

The clamp’s jaws are usually made of steel, sometimes with a layer of plastic applied to reduce scarring on soft materials to be clamped. A spring holds the jaws tightly closed, until the action of squeezing the handles together opens them. Spring clamps are sold in various sizes that open one, two, three, or more inches.

Strap Clamp. Also called web or band clamps, these clever devices rely upon a beltlike length of webbing to tighten joints in a structure. A mechanical device functions as a kind of elaborate buckle, with a ratchet that allows the one-and-a-half-inch-wide belt to be tightened.

Belt clamps are especially useful in furniture work, tightening frames and cases (even round ones), and those seemingly impossible clamping tasks that most clamps just don’t seem to suit.

As with any clamp, make sure you remove any extra glue from the clamp. Not only can excess glue cause the strap to adhere to the clamp, but it may leave an abrasive residue on the strap for the next job. Either way, you can mar your work.