Screws For Woodworking

A few years ago drywall screws grabbed the attention of woodworkers. They go in faster, hold tighter, and don't require the typical pilot hole, shank hole, and countersink needed by regular wood screws.

But drywall screws may not be the best answer either. Recently, I've switched to particle fxxird screws.

heat-treated. Both particle board screws and drywall screws are heat treated. This gives them the strength needed to power-drive them into steel studs with no pilot hole.

This feature attracted woodworkers because you could drive them straight into hardwoods (even with no pilot hole) and they wouldn't break or twist apart. (Although this process is fast, it's probably not the best procedure. More on this later.)

head shape. Apart from being heat-treated, there are some differences between drywall, particle board, and standard woodscrews. Drywall screws have a trumpet-shape on the back of the head, while particle board and standard screws have a sharper V-shaped head. (The trumpet shape lets the drywall screw head pull down slightly belowr the surface without tearing the drywall paper.)

threads. The most important difference between these screws is the thread angle and shape. Typical particle board and drywall screws have threads that climb up the shaft at a steeper lead angle (20°) than on standard woodscrews (15°), see the drawing above. This means you can drive them in quicker.

For example, a 1 '/Along standard woodscrew takes about 15 full revolutions of a screwdriver to drive it in flush. But a lW-long particle board screw only takes about 10 revolutions.

Some particle board and drywall screws have even steeper threads (25-30°) for faster driving (trade-named "Kwixin"). They may also have two separate threads (called a double lead) that climb up the shaft like the red and white stripes on a barber pole. (This is shown on the drywall screw in the drawing above.) Since a double-lead thread has twice as many threads, it tends to hold better, particularly in softwoods.

particle board screws. More important than the number of threads is the depth of the threads. The thread of a particle board screw is deeper and sharper than a drywall screw. Commercially, a deep-thread screw is called a "Lo-Root" screw since the center shaft between the threads (the "root" of the screw) is much thinner.

This produces deeper, sharper threads that slice their way into the wrood. (They have a smaller "thread" angle, see drawing above.) Once the screw is in place, the deep threads hold tight.

conclusion. Although I'm not ready to give up the old slot-head woodscrew, I have been using particle board screws more often. And recently I've gotten very interested in the Robertson square-drive version, see box on the next page. (I used Robertson screws on the computer desk and printer stand shown in this issue.)

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