Choosing an Electric Drill - Chuck Size and Type
By: The Working Man
The chuck on a drill is a special clamp or sleeve that is
designed to expand or contract to hold a variety of sizes of
drill bits (or other rotary tools).
The size of the chuck determines the shaft size that can be
driven by the electric drill. Ordinarily
the larger the
chuck the more powerful the motor of the electric drill must
be, because the larger the chuck, the larger bit shaft the
drill will accept.
High speed steel "HSS" and other kinds of twist drill bits
usually drill the same diameter as the drill bit's shaft.
With hole cutters, such as the Forstner, Auger, and Spade
drill bits, generally the shaft is much smaller than the
cutting edge of the bit.
The most common chuck sizes are three eighths of an inch and
one half an inch. The three eighths chuck will only accept
accessories with shafts up to three eights of an inch. The
one half inch chuck is a heavy duty chuck that will accept
accessories to the electric drill with up to a one half inch
shaft. Three eighths of an inch is suitable for most
The more common drills have chucks that require a chuck key
to enlarge or shrink the chuck teeth to fit the particular
shaft being used. However, getting more and more common
lately is the keyless chuck which can change the size of the
chuck teeth opening by simply turning the chuck section of
the drill by hand.
Keyed chucks can come with many different size key-holes and
tine depths which can cause problems keeping track of the
correct key for the drill needed unless you somehow attach
the key to the drill itself.
The keyless chucks are much easier to use since you will not
have to constantly be looking for the key in order to change
out the different accessories and attachments.
There are also SDS chucks, particularly in the case of
hammer drills, that require a specific set of drill bits
that are not that easy to come by and are not recommended
for the do-it-yourselfer, but may be needed if you are a
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