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ciently in wood, however,
if
the point is altered
from the original 120
degree angle to a much
sharper angle of ap-
proximately 70 degrees.
Most any standard
bit may be used for
wood drilling in the drill
press. Slight alterations
may be necessary in
some cases.
The solid
center wood bit com-
For Metal
For Wood
monly used with the hand brace can readily
be reworked for drill press use by filing the threads
off the point and by cutting off the enlarged
adapter section at the end of the bit shank.
The Spur Machine Bit is probably the best bit
for wood drilling with the drill press. It combines
the best qualities of the twist drill and the standard
wood bit. Its stiffness and cutting spurs combine
Solid Center
Wood Bit
Spur
Machine Bit
Double lip
Counter Sink
to make a better tracking bit which drills an ex-
ceptionally smooth true hole in wood.
The Expansive Bit is a handy t~ol for drillin~
large holes. With this tool you can drill a variety
of large hole sizes without having to buy separate
large diameter drills for each hole size.
As
is true
with any of the wood bits when used in the drill
press, the screw point must be filed to a brad
point. This prevents the coarse screw threads from
biting into the work and lifting it from the table.
The Double Lip Counter sink is more desirable
than the rosette type. for drill press use. It will cut
cleaner and is less apt to load up with chips and
gum under continuous operation.
DRILL SHARPENING:
To maintain the accuracy and cutting efficiency of
your twist drills, extreme care should be exercised
during grinding. The two cutting lips must be of
equal length and their angle in relation to the axis
of the drill must be equal.
Relieve the metal
gradually behind the cutting lips so that the angle
at the heel of the cutting edge is approximately 12
degrees on a side less than at the cutting lip.
4
Length of Cutting lips
must be equal
OPERATION:
Heel of
Cutting Lip
When the drill press is used for wood working it is
advisable to fasten a smooth level auxiliary table of
Y4
inch p.lywood to the metal table using countersunk
flat head screws or bolts.
This auxiliary table not
only increases the working surface available, but pro-
vides a surface on which auxiliary fences, shaping,
guides, pivot pins and other similar units may easily
be used.
This auxiliary table also will reduce the
danger of drilling through the work piece 'into the
metal table.
If
the drill is to pass completely through the work
piece it is advisable to place a piece of scrap wood
under the work piece at the point of breaking
through to prevent splintering and mutilation of the
lower surface as the bit breaks through.
Ano~her
method of preserving the surface, at drill break
through is to reverse the wood and drill through
from the opposite side as soon as the drill point
emerges on the lower 'Surface.
Due to variation in the bit pattern, the type, hard-
ness. and grain of the material, and the depth and
quality of the hole desired, it is impractical to at-
tempt to establish a fixed table of drill feeds and
speeds for boring in wood.
It is best to follow this
general rule: the larger the hole and the harder the
material the slower the feed and speed. Start any
drilling operation with a moderate feed and speed,
increasing either or both after noting the effect on
the drill.
In wood drilling operations, drills up to
¥.t
inch in
diameter may generally be run at 1800 to 3000
RP.M. without burning while bits
Y4
inch in diameter
and over cannot generally be run over 2400 RP.M.
without burning. Multi-spur bits, expansive bits and
hole saws should never be operated over 750 RP.M.
In general, if the drill smokes in the hole, reduce the
feed and speed to prevent burning.
When drilling metal. if it is noted that the drill
wears away at the extreme outer corners of the cut-
ting edges, it is an indication of too much speed.
Likewise
if
the drill chips on the cutting edge, it is
an indication of too heavy a feed. Very small drills
are generally designed for high speed and light feed
and should be used accordingly for best results.
A straight piece clamped to the table as a guide
or fence has many uses, as in drilling several holes the
same distance from a common edge or as a guide in
grooving or fluting operations.
The work piece should be held securely on the
table either by clamps or pins to prevent turning
with the drill.
A drill vise is an inexpensive and very handy unit,
designed to hold various odd shaped work pieces for
drilling. Cylindrical work pieces such as dowels, or
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