The hole story

For large-diameter holes in wood, using the right bit can make the job easier.

From the days of craftsmen using a brace and bit to make large-diameter holes, the general design of bits has changed little over the years. However, manufacturers continue to refine the bits to help them make faster, cleaner holes in wood with less effort.

“The design of bits hasn’t changed as much as the metallurgy in the bits,” says Peter Chiello, accessories product manager at Milwaukee Electric Tool Co., “It allows them to last longer and be easier to use.”

Getting the most work done still lies with bit selection, say the experts.

Boring bits fall into three general
categories, says Brian Kagen, DeWalt accessories manager. “For making rough holes in wood, contractors
generally rely on a spade bit, auger bit or self-feeding bit. Each type has a fit for certain jobs.”

Spade bits – occasionalholes from 1/4" to 1 1/2"

Spade bits are the most inexpensive wood-boring bit. With a cutting
capacity that ranges from 1/4" to 1 1/2", these bits are great for occasional hole-drilling, says Tim Kruto, twist drill and wood-boring product manager at Bosch Power Tool and Accessories. “Spade bits use a scoring edge to bore into wood and can produce a relatively smooth hole. However, spade bits don’t self-feed, so the operator must apply pressure to make the hole. If you are making more than five or 10 holes, an auger bit will be a better choice.”

While most spade bits are similar, Bosch offers the RapidFeed spade bit that uses a combination of different bevel geometry on the cutting edges and a screw-type tip that pulls the bit into the wood. “The combination of the
cutting edge and the screw tip makes the RapidFeed bit very aggressive. It will make a hole three times faster than a conventional spade bit,” Kruto says.

Unlike other bits, spade bits can be used with smaller drills. “A 3/8" drill can handle most spade bits and can be used with cordless drills,” says Kagen.

Making holes with spade bits requires frequent backing out of the hole to clear wood chips. “The bevel on the cutting edge of the RapidFeed bit will clear the chips out so it doesn’t have to be pulled from the hole to clear chips,” Kruto says.

Spade bits may have a flat edge
on the shaft to prevent the bit from spinning in the chuck. “Some are
available with a hex shaft so they can be used in quick-change bit systems,” says Kagen.

Spade bits that hit nails may chip or bend the cutting edge and affect
cutting ability. “The edges can be touched up with a file, but most users just replace the bits because they are inexpensive,” says Kruto.

Auger bits – production
drilling from 5/8" to 1 1/2"

Auger bits are considerably more expensive than spade bits, but that price returns fast, easy hole-drilling with little need to back out the bit to clean out chips, says Kagen.

Auger bits come in a few variations that affect productivity. The ship auger bit has two cutting edges on the tip; a spur or scoring auger bit has a cutting edge coming off of one drill flute and a spur off the other. They are used for high-production drilling through studs, joists and subflooring.

“Ship augers usually have a hollow center flute design that moves chips out of holes quickly so they don’t plug the flute,” says Kruto, “Spur augers usually have a solid center flute that gives the bit more rigidity for drilling through hard wood but may need to be backed out to clear chips,” he says. Spur augers also tend to make a cleaner-looking hole.

Ship and spur auger bits have a screw tip that draws the cutting edges into the wood. Users will find dual cutting edges on all DeWalt wood-boring bits, says Kagen. “Electricians like the dual cutters because they can go through several studs at once. They also come in 6" and 18" sizes to match the depth of the hole and the clearance the tool has,” he adds.

Dual-edged ship augers can
withstand hitting nails better than spur augers. “If a spur or scoring auger hits a nail, it’s likely the spur will be broken off. With a dual-
cutting ship auger, the edge may be nicked by the nail and can be touched up with a file,” Kagen says.

Ship or spur auger bits should be used with a 1/2" corded drill.

Self-feeding bits – for
holes larger than 1 3/8"

On jobs where many holes are larger than 1 3/8", the experts
recommend self-feeding bits.

“Self-feeding bits are extremely fast at making holes from 1 3/8" to
4 5/8"”, says Chiello. “They can drill a hole through studs in as little as three seconds. They are very fast, aggressive bits.”

High-torque drills are needed to muscle these bits through wood. “For holes larger than 3", the bit should run only at 450 rpm and no faster than 1,200 rpm. Bits that are
2 9/16" and smaller can run faster than 1,200 rpm,” says Chiello.

The self-feeding bits are designed not to plug as they plow through wood. “They also have a screw tip that draws the bit into the wood. Self-feeding bits are available with a finer threaded tip for use on hardwoods and a coarser-threaded tip for use on softer wood.

Although hitting nails is hard on self-feeding bits, the bits can be resharpened. “You can send them to a sharpening shop, or follow the directions that come with the self-feeding bit. It’s a similar process across all brands, but it can vary between bit brands,” Kagen says.

Extend your reach

Many of these bits can be
outfitted with extensions for greater reach. Extensions come in 6", 12", 18" and 24" sizes and slip over the bit’s shaft and tighten with a hex wrench. Many are available in quick-change systems.

Published in the March 2004 issue of Contractor Tools and Supplies magazine.

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