Drilling and Boring Tools
Titanium-coated, Brad-pointed, and Spade Bits
Titanium-coated bit. Some bits feature titanium-nitride or -nitrate coating. The hard, slick finish helps them cut better and last longer, the manufacturers say. WOODŽ magazine testing found that the titanium coating offers few advantages for drilling wood. If you drill metal frequently, though, the gold-colored bits represent a good buy.
Bradpoint bit. Many woodworkers turn to brad-point bits for precise drilling, particularly for dowel holes. This bit looks much like a twist drill, except at the tip. There, it's ground nearly flat, but with an extended point in the center -- the brad point -and a pair of cutting spurs, as on the bit shown in Photo 2, above.
The bit's extended point makes lining up on a mark easy. The spurs minimize splintering, making a cleaner cut. And the bottom of a hole drilled with a brad-point bit is nearly flat. Run brad-point bits at about 1,200 rpm for 1/8", 1,000 rpm for sizes up to 1/4", and 750 rpm to 1/2".
Allowing chips to pack into the flutes on any twist-type drill can overheat the bit and burn the wood. To avoid problems, back the bit out of the hole often to clear the chips.
Spade bit. The flat blade shown in Photo 3, above, distinguishes this bit from other drills. Spade bits cost little and work well for general drilling in hard or soft woods. They're a good way to go when drilling holes beyond normal twist-drill size, from 1/2" up to 1 1/2" in diameter. You can buy spade bits as small as 1/4".
These bits bore relatively quickly. Don't rely on them for your finest cabinet work, however. Spade bits don't make particularly clean holes -- they seem to scrape and tear the wood more than they cut and slice it.
Variations on the standard spade bit, such as Irwin's Speedbor 2000 and the Vermont American Wood Eater, Photo 4, above, offer refinements for faster, cleaner boring. The Wood Eater has a self-feeding screw point. Another style from Vermont American called Around the Corner, Photo 5, below, lets you drill, as the name implies, a curved hole -- handy for electrical wiring in home remodeling, among other things.
Space bits and their brethren call for lower speeds. In hardwood, limit the speed to 1,500 rpm for spade bits up to 1", 1,000 rpm for larger ones. Speedbor 2000 bits can go to 1,800 rpm for all sizes. Recommended speed for 1/2" and 5/8" Wood Eater bits is 700 rpm; larger sizes, 600 rpm. Go slow in curves, too: operate the Around the Corner bit in the 600-850 rpm range.