Spade bits have a center locating point and two sharp, flat cutting edges that work with a
scraping action to bore holes in wood. Spade bits are inexpensive and cut quickly, but the
holes they make are rougher and less accurate than the holes made by other bits. This makes
spade bits a good choice for general boring and rough carpentry but less appropriate for
jobs such as making dowel holes.
Using a Spade Bit
Start the drill at a slow speed; as the bit enters the wood, slowly increase the speed to
full - spade bits are most efficient at around 1,500 revolutions per minute (rpm). Retract
the bit frequently to clear waste from the hole. This makes cutting more efficient and
lessens the chances of overloading the drill.
If you want to drill a hole that does not go all the way through a piece of wood, allow
for the fact that the point will go deeper than the flat cutting edges. Spade bits leave
rough, splintered exit holes.
Spade bits are easy to sharpen with a file.
The spurs included on some spade bits are brittle and easily damaged. Store them in a rack
or a sheath so they won't bang against other tools. Rust blunts sharp edges, so it's best
to lightly oil bits before storing them for long periods of time.
Purchasing
Spade bits range in size from 1/4 to 1-1/2 inches. Double-spur spade bits have spurs that
dig into the wood at the circumference of the hole. They cut faster and cleaner than a
standard model.
Substitutes
An alternative to the spade bit is an auger bit. The auger is a slow-speed wood bit
designed for hand-drilling. A threaded screw on the tip of the bit centers it and draws
it into the work, while a pair of spurs slice the circumference of the hole and two
lateral cutters remove wood shavings. The bit's deep flutes quickly eject wood chips
as you drill. Auger bits come in numbered sizes that represent 16th-inch increments.
Another alternative is the forstner bit. These bits are designed for use in a drill
press, but can also be used with a standard electric drill. Use these bits to drill
precise, smooth-sided holes in wood. Forstner bits can drill perfect flat-bottom holes
without breaking through the back of the work, and can also drill precise angled or
overlapping holes without slipping.
A third alternative to the spade bit is a multispur bit. A self-feeding multispur bit
bores holes large enough for running conduit or pipes through wood. To provide fast
feeding action, a replaceable threaded screw point pulls the bit into the work. The
bit fits 1/2-inch drills only and requires extremely high torque.
Caution
- Keep bits sharp.
- Clamp work securely.
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Brought to you by Book of Skills and Tools and New Complete Do-It-Yourself Manual
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