Popular Woodworking 2003-02 № 132, страница 71

will split in two when the screw is driven. Splitting is a problem when using drills in a fastening application that's solved by pre-drilling a pilot hole. When you're attaching hardware, locate and mark the location where you need to put the screw. By drilling a pilot hole with a drill bit equal in diameter to the screw shank (minus the width of the threads) you'll not only get the screw in exactly the right location, but also keep the screw shank from dramatically pushing the wood fibers apart, splitting the board.

Fastening two pieces of wood with a screw is easier and more successful by using a clearance hole. Similar to pilot-drilling, a clearance hole is a pre-drilled hole slightly larger in diameter than the screw including the threads of the screw. The clearance hole is drilled only into the outer piece of wood. This is particularly advantageous when using screws that have threads the entire length of the shaft. If the two pieces move apart slightly during screwing, the threads biting into the first piece will keep it from pulling the two pieces tight. With a clearance hole in the first piece, all the pulling takes place in the secondary piece, making a snug joint.

Another important drilling and screwing topic is countersinking. Flat-head screws are used to keep the screw from protruding above the wood. The tapered part of the screw head can keep the screw from seating flush to the wood. The photo on the previous page shows in detail the benefit of countersinking a screw.

Those are the basics of using a cordless drill. It's important to choose the right cordless drill for your work. If you haven't read through the accompanying drill review, you should take a minute to do so before you go shopping for a cordless drill. PW

RIGHT TOOL, RIGHT SPEED

There's a great selection of specialty tips and bits for use in today's corded drills. Just a handful are shown below, (with their general uses listed in detail) offering improved performance for big and small holes, as well as driving and setting screws. To optimize bit performance, the proper speeds are beneficial.While you can't

tell the exact speed the drill is spinning at, you can usually choose a high or low speed. By adjusting your pull on the trigger, you can further refine the variable speed. In short, the larger the bit the slower the optimum performance speed.

Forstner Bit • Best used for drilling holes larger than ³/4" in diameter, the Forstner shown uses a saw-toothed rim design, improving cutting speed and reducing rim heat that can damage the cutting edge. Forstners offer clean, shallow holes with good control.

Countersink • When using flat-head screws, the object is to keep the screw head flush, or slightly below the wood surface.While you often can force a flat-head screw to push into softer woods, it's still easier to cut a tapered recess for the screw head. The countersink does this to whatever depth is required.

Spade Bit • This is another option for holes larger than ³/4" in diameter. For holes larger than 1V2" you should choose a hole saw or Forstner bit. Spade bits are best used for rough work, leaving more ragged edges in holes and are harder to control. But they are significantly cheaper than Forstner bits.

Hinge Bit • Designed for use in accurately centering a screw in the hinge holes, this bit's sleeve hugs the hole rim, automatically centering the bit, then retracts as the bit is plunged. If you've ever fought with a butt hinge, you know the value of this bit.

Twist Bit • This is the bit most of us think of when "drill bit" is spoken. The tip offers a shallow taper on the cutting edge that is best suited for use in metal work.This bit still appears in lots of woodshops because of its inexpensive nature, but it isn't the best choice for drilling in wood.

Brad-point Bit • The better option in wood is a brad-point bit that uses a center spur to accurately guide the bit as it bites into the wood.This reduces wandering almost entirely, but make sure you start the bit in the correct space, because the spur will guide the bit right where you aim it. A variation on the brad point not shown is a bit with spurs on the outer edge of the bit point as well. These extra spurs provide a cleaner hole, but also give a more aggressive and faster cut.

Magnetic Driver • This accessory should come with every cordless drill. It extends the reach of the drill, allows for a number of different tips (Phillips, square, slotted,Torx, Allen-head) and is magnetized to hang on to the screw. A number of sets now available offer this type of driver with either a quick-change mechanism for pilot and clearance drill bits, or even a two-in-one feature with the bit sleeved inside the driver.

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