Drilling and Boring Tools
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.
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. WOOD® 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.
Powerbore, Auger, Forstner, and Multi-spur Bits
Powerbore bit. Stanley's Powerbore, Photo 6, left, drills a cleaner hole than the space bit. Available in diameters from 3/8" to 1" in 1/8" increments, these bits handle end-grain drilling particularly well. The long, brad-type point guides the bit, and makes it easy to center on a mark. The bit cuts relatively quickly, but doesn't carry chips out of the hole. So, if you're drilling a deep hole, withdraw the bit frequently to clear the chips. Speeds in the vicinity of 500-750 rpm will work fine.
Auger bit. Before power drilling, there was the brace and auger bit. Many tool dealers still sell augers with the traditional tapered square shank end for use with a brace. You can also buy a straight-shank version to fit the chuck on your power drill.
Augers, like the one shown in Photo 7, above, bore smooth holes. They're well-suited to deep-hole boring because of their length: A 1/4" auger is nearly twice as long as a 1/4" twist drill. And you can buy even-longer ship augers and pole augers. While some augers are sized in inch fractions, you'll still find many identified by the traditional number system. Don't let it throw you, though. The number simply refers to the bit diameter in 16ths of an inch. So, a bit marked 10 would be 10/16", or 5/8".
Most augers self-feed with a screw tip. When power-drilling with an auger, don't run the bit at more than 600-700 rpm.
Forstner bit. A true Forstner bit, named after its inventor, has only a small center point, shown on the left in Photo 8, above. The outer rim guides the bit instead of the center point, enabling the Forstner to cut holes with nearly flat bottoms and smooth, true sides. That also means you can cut any arc of a hole on a workpiece -- the center doesn't have to be on the stock. The small point makes the bit difficult to center on a mark, however.
These are expensive bits, but to many woodworkers, they're the ultimate drilling or boring tool. Sizes generally run from 1/4"-2". For maximum accuracy, you'll want to use the Forstner bit in a drill press. Clear the chips often, and run the bit at a moderate speed to prevent heat damage to the cutting edge. Try 700 rpm for bits less than 1/2" diameter, 500 rpm for bits up to 1", and 250 for those larger than 1". Carbide-tipped Forstner bits are available.
Multi-spur bit. Though this one is often called a Forstner bit, it isn't. The teeth around the multi-spur bit's rim (shown at the right in Photo 8, above) are the difference between it and the Forstner type.
These bits are expensive, but cut cleanly and without splintering. Multi-spur bits work well when drilling into a workpiece on an angle. They do a great job with overlapping holes, too.
Sizes range up to more than 4". You should consider any large one a drill-press-only bit. Even the smaller sizes are much easier to keep under control with the drill press. In hardwood, you can run bits 1" or smaller at about 500 rpm. Slow down to 250 rpm for bits from 1" to 4".
Holesaw and circle cutter; Specialty bits
Holesaw and circle cutter. Instead of taking out the inside of a hole as chips, you can remove it in one chunk with a holesaw or circle cutter, both shown left. They're the tools to turn to when you need a really large hole.You'll find holesaws up to 6" in diameter and circle cutters that adjust to 8" or more.
Holesaws use fixed-size cutters. The cup-shaped blade fits onto a mandrel equipped with a twist drill in the center. The drill bit acts as a pilot for the tool.
The circle cutter (sometimes called a fly cutter) adjusts to any diameter within its range. It also employs a twist drill for a pilot, but cuts with a single blade.
With either, the inside depth of the tool limits the cutting depth. To go through thick stock you can drill as far as the tool will go, flop the workpiece, then drill from the back, using the pilot hole as a guide. With a holesaw, you can withdraw the tool when it bottoms out, break the core out of the stock, then saw farther.
Clamp the workpiece firmly when using either one. Holesaws, especially those 1" or less, work well with a portable drill (but hang on tight). Larger holesaws and any size circle cutter should be used only in the drill press. Limit the speed for either tool to250 rpm.
Specialty bits. If you use a lot of screws in your projects, check out screw pilot bits. These inexpensive bits drill the pilot and shank holes for a screw and form a countersink for the head, all in one operation. Other bits of this type counterborte for a plug. The three bits at the lower left side of Photo 10, below, are typical.
For attaching hinges and other hardware, a Vix bit, shown at the upper right of the photo, comes in handy. A sleeve on this bit fits into the countersunk screw hole on the hardware item, automatically centering the bit, which then extends from the sleeve to drill the screw pilot hole.
An expansive bit like the one shown in Photo 11, below, bores holes of many sizes. A sliding cutter sets the diameter -- useful if you need to bore odd-sized holes. The two available sizes cover a range of hole diameters from 5/8" to 5". Interchangeable cutters give the bit shown a range of hole diameters from 5/8" to 3". Power-drilling with one can be problematic, though. You'd be better off using one only with your brace.
General Tips for Drilling
- Back the workpiece with scrapwood to minimize splintering when the bit breaks through. This doesn't always guarantee a splinter-free hole when you're using twist drills, however.
- Feed the bit steadily into the work. Don't force the bit, trying to make it cut faster than it's able to. On the other hand, don't feed it with such light pressure that the bit rubs without cutting. Either situation can overheat the bit, dulling it and possibly burning your project part.
- Always secure the workpiece solidly. When possible, use a drill press, and clamp the piece being drilled to the table. When using a portable drill, clamp the workpiece, and use both hands to hold the drill. Be sure to use an auxiliary side handle when using a large bit in the portable drill.
- Before you start the drill, chuck the bit tightly. Give the chuck key a twist in each of the three holes around the chuck body.
- Where eye protection whenever you're drilling.
- Clear chips from the hole as you drill. If you're drilling metal, don't sweep the chips away with your hand -- they can be razor sharp. Instead, blow them away or use a brush.
- Remember that the bit will be hot, possibly very hot, after drilling. Don't grab hold of it as soon as you pull it from the hole.
- Use only sharp bits. You can sharpen twist drills yourself -- although the smaller ones can be difficult to sharpen well. Spade bits sharpen easily.
- When you have a choice, buy bits made of high-speed steel (HSS). They'll hold an edge longer, even if you run them hot. Carbide-tipped tools last a long time, too. (But don't think that carbide-tipped twist drills for masonry drilling will help you in woodworking. They won't.)