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Drilling and Boring Tools

Intro, Standard, and Improved Twist Drill

Intro, Standard, and Improved Twist Drill

Need to make a hole in wood? You'll find a wide array of bits suitable for drilling and boring in wood. Here's a look at some of the popular choices.

Standard twist drill. This bit, the type shown at far left in Photo 1 below, is the first one you're likely to think of for drilling holes up to 1/2" in diameter in wood, metal, or plastic. Inexpensive and readily available, twist drills come in a vast array of sizes. The most common bit sizes are the fractions of an inch from 1/16" to 1/2" in 1/64" increments. (You can buy inch-sized twist drills in diameters from 1/64" to 1 1/2".)

But, twist drills also come in wire-gauge sizes numbered from 1 through 80 -- all less the 1/4" diameter. (Larger numbers are smaller drills.) Need more sizes? Try letter bits from A to Z. These range from just under 15/64" to a little over 13/32" in diameter, with drill size increasing as you go up the alphabet. If those aren't enough, you'll find bits in metric sizes, too.

You could gather scores of twist drills without any two being the same size. But for most woodworking chores, a set that ranges from 1/16" to 1/4" by 64ths plus the four bits from 5/16" to 1/2" by 16ths will suffice. You can buy the larger bits with reduced-size shanks.

Twist drills work best at higher speeds. In hardwood, you can run bits up to 3/16" in diameter as fast as 3,000 rpm. Cut the speed to 1,500 rpm for bits up to 3/8", and slow down to 750 rpm up to 1/2".

Improved twist drill. Starting a hole with a standard twist drill can be irksome, particularly with a hand-held drill. (For best results, center-punch marks for drilling, even when using a drill press.) So often, after positioning the bit where you want the hole, you pull the trigger and the bit wanders off across the wood, missing the mark completely and marring the surface, too.

Tool manufacturers have brought out new bits that reduce this tendency. Split points, pilot points, and different point angles are some of the tactics used to make premium drills such as the gold and silver ones shown in the photo, above, easier to start.

In addition to the modified tip, many of the new premium bits feature changes to the flute and body aimed at reducing friction and wear while increasing cutting ease. Such bits require less power to drill a hole, so you can drill more holes per charge with your cordless drill. The pilot-point type exits more cleanly than other twist drills, too.

Continued on page 2:  Titanium-coated, Brad-pointed, and Spade Bits



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