Woodworker's Journal 2010-34-2, страница 57

Countersink Options:

Countersink bits (above)

Getting the Angle

Countersinks are available

woodworking screws you might encounter in the Li .S.

with cones shaped to create six distinct chamfer angles — 60°, 82°, 90°, 1(M)°, 110° and 120° — designed to match a particular screw's head angle. The two most commonly used angles in woodworking are 82° and 90°. Those two particular angles are based on the standards to which the screws are manufactured and used. Screws with 90° heads are made to the ISO Standard; they're usually metric and far more common overseas. Most recognized in North America is the Unified Thread Standard of 82°, which matches just about all

and Canada. However, both standards of countersinks are readily available here.

Since chances are good that you'll only use screws with 82° heads, does it make a difference which countersink you buy and use? Well, that depends. If you take at look at the Illustration (next page), you can see how the typical 82° woodworking screw seals in a countersink. W ith the 90° countersink on the left, because of the 8° difference the very bottom of the screw head makes contact with the wood first, leaving the sides and top of the screw

unsupported. The screw must be further tightened lo bring llic rest of the head into contact with the countersink, creating a greater force on the wood al the bottom. Essentially, what you're doing is forcibly elongating the countersink by overdriving the screw. With the 82° countersink on the right, all surfaces of the screw head make contact with the wood at the same time and with an equal amount of force.

Common sense will tell you that matching the screw to the

Shop Test continues on page 60 ...

come in a wide variety of styles and sizes to suit particular woodworking tasks and personal preference.

Woodworker's Journal April 2010

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