Popular Woodworking 2007-02 № 160, страница 58

Woodworkers use clamps for all sorts of purposes - to create pressure when gluing, to secure parts during assembly, to hold parts while working on them. There are many types of clamps available, but one of the most versatile and powerful of all is the wooden-jawed handscrew.

A typical handscrew consists of two hardwood (usually maple) jaws with beveled ends. The clamps are adjusted and pressure is created with a pair of parallel screws (also called spindles) that pierce the jaws. Wood handles on the screws allow a better grip for creating torque.

Handscrews are made in graduated sizes. They are typically measured in three ways, the first being jaw length. Handscrews with jaws as short as 4", to as long as 24", are available. The second measurement is the maximum amount the jaws can be opened or separated. This distance is a function of the screw length, and its measurement is called the clamp's capacity. Some larger handscrews have a capacity of 17". The third measurement is the handscrew's reach. This is the distance from the front of the jaw to the center screw. The reach on larger handscrews can be as much as 12".

Handscrews with 10" to 12" jaws, with 6" to 8" capacity, and 5" to 6" reach will meet most of your woodworking needs.

Compared to some woodworking tools, the handscrew is a relatively new innovation. It was first produced in the form we recognize in the late 19th century, even though woodworkers used similar but cruder, wooden clamps for many centuries previous.

Wood v. Metal Threads

There are two versions of hand-screws. The older 19th-century

type is the more simple. It has four parts, all made of wood. These are two wooden jaws with two wooden screws. The handles are integral parts of the screws. This type of clamp is no longer commercially made. Although these older handscrews are frequently sold on the antique tool market, I do not recommend them (though they deserve to be preserved). The old, brittle wood does not hold up to the wear and tear of shop use. Woodworkers who prefer all-wood handscrews should make their own.

The second and more widely recognized handscrew was developed during the 20th century and is still being made today. While retaining the two wooden jaws, its screws are threaded steel rods and the wooden handles are applied to these rods. Within the last decade or so, large numbers of these handscrews have been imported from China and other developing countries. The quality of these imported clamps varies considerably. You usually get what you pay for.

Each type of handscrew - the all-wood, or the steel thread - is used similarly. However, each also has advantages over the other. Your own needs should guide your decision to either buy handscrews or make your own.

Wooden Handscrews: Flexible but Fragile

Making an all-wood handscrew is not a complicated woodworking project (see the story on page 82). However, you will need a thread-box and tap, and a lathe. The holes in the lower jaw (as shown in the illustration) are both threaded.

Handscrews come in two principal varieties: all-wooden clamps and those with metal threads. Both have advantages and limitations, so I think it's handy to have both in the shop.

The center hole in the upper j aw is through, while the other hole in that jaw is blind. The most desirable feature of this older version of handscrew is provided by the wooden screws. When the clamp is tightened the rear screw bows slightly. This flex allows the screw to function as a spring. If the clamp is loosened slightly or the work shifts, the clamp adjusts and does not immediately fall out of position. This makes the all-wood handscrew superior for assembly or for fitting, or for work where shifting or adjustment is going to happen. It is a pain to have your work shift and all the handscrews fall off, which can happen with metal-threaded handscrews.

The disadvantage of the all-wood handscrew is that the jaws do not pivot nearly as much as the steel-spindle variety and so it is not the best choice for irregular shapes. Also, the wood threads have very short grain and are prone to damage from the everyday bumps and bangs that occur on a workbench.

If an all-wood handscrew is over tightened, the threads can

by Michael Dunbar

A chairmaker since 1971, Michael is the founder of The Windsor Institute in Hampton, N.H., where he teaches hundreds of students each year to build Windsor chairs. For more information, visit thewindsorinstitute.com.

With a wooden handscrew, the rear screw flexes under pressure, allowing the clamp a springy grip. The bowing is almost imperceptible to the unaided eye, but it allows the clamp to keep a tenacious grip. Note the chipped threads on the screws, a result of 10 years of use.

strip and break away. Another concern about over tightening is that the rear screw will break. Fortunately, it really takes some inattention and muscle to cause this type of damage. As these handscrews are shop-made, you can always make a replacement screw. But because these clamps

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