10th in a series by Barb Siddiqui
Driving a woodscrew with a simple screwdriver seems so basic, it shouldn't need instruction. But why does the thing always squeak like it's being killed, and become a power struggle during the last half-inch, when it started so easily?
There are some tricks to this that are worth knowing. If you look at a standard woodscrew, you'll see the shank beneath the cutting threads is smaller than the unthreaded shank below the head. Drilling pilot holes a bit smaller than the inner diameter of the threads will ease the screw into the wood and prevent splitting, but without a wider shank hole at the top, the screw has no clearance to do its work.
Ideally, when joining two pieces of stock with screws, the woodscrew selected will slide clear through the top piece, and all of the threads will seat in the bottom piece, pulling the two together when the angled head settles into its countersunk position. Yes, that is three pre-drilled holes: a pilot hole, a shank hole and a countersink, and yes, it is a pain. Even then, you may want a counter bored hole above all that, to set in a wood plug and hide the screw head.
There are ways around this, though old-fashioned wood screws are the strongest mechanical application you might ever need. One way around it is to buy a set of pilot bits for the drill that incorporate pilot hole, shank hole and countersink, all in one operation. They are pricey, and you'd need one for each size screw you commonly use.
Another approach is to buy drywall or deck screws. They are somewhat weaker, and have less holding power, but have a straight shank and are usually threaded up to the head of the screw. On hardwoods, one size pilot hole, less than the diameter of the shank, will do. On softwoods, a pilot hole is usually not necessary at all. If you use these, clamp your wood pieces together or the threads may push the two apart as they enter the lower workpiece.
There are many types of screws available: pan-head screws with a straight shank and an auger-cut tip are ideal for pocket-hole joinery, pulling the workpieces together. There are special wood screws with serrated edges on the threads to cut into the workpiece and avoid splitting. There are 'production' screws with a straight shank meant for use in plywood and medium density fiberboard (MDF.) You can choose a single thread or a double-thread screw, flat heads, bugle heads, round heads or pan heads.
In spite of the bewildering variety, there are some general rules to keep in mind when selecting screws and their drivers. You should judge what length screw to use by the thickness of wood you are using as a top piece. Generally, each job requires a screw that is three times the thickness of the wood being attached. Half-inch case sides? Use one-and-a-half inch screws. Quarter-inch back board? Use three-quarter inch screws.
The screwdriver heads or drill bit drivers matter also. Whether straight, Phillips or square drive, be sure the tip of the driver fits and fills your screw head. There are different tips for different size screws, and the way your tip seats in the screw head will determine how much power you have to drive the screw accurately.
By hand, hold the screwdriver perpendicular to the workpiece and drive the screw in a straight line (use short, stubby screwdrivers in tight spaces.) When using a power drill, be sure it is a variable speed model, go slowly, and push with some force after the screw has started itself, so the bit won't slip out of the screw head.
It also helps to roll the screw threads in a little beeswax for lubrication. Toilet-sealing rings, found in any hardware store with the plumbing supplies, are an inexpensive source of beeswax. Don't use soap; it will react with metals and stain your wood.
One last tip: brass screws are classy looking, but they are soft and the heads strip out easily. If you want to use brass screws, first sink a steel screw of the exact same size, remove it, and then insert your brass screw. Brass is also best in oak, as steel screws react with its high tannin content and lead to ugly stains on the workpiece.
If a project is worth doing, then it is worth doing right, so take your time, learn to use even the simplest of tools properly, and your woodworking results will show it.