BORING TOOLS--BORING.
=36. Brace or Bitstock.=--Fig. 73 illustrates a common form of brace.
This tool is used for holding the various kinds of bits which are used
in boring, reaming, etc.
The ratchet brace consists of essentially the same parts but in
addition has an attachment which permits of the crank’s acting in one
direction or the other only. It is a necessity where the crank cannot
make an entire revolution, and is very convenient for boring in hard
wood, or for turning large screws.
[Illustration: FIG. 73.]
[Illustration: FIG. 74.]
To insert a bit, hold the brace firmly with the left hand, revolve the
crank until the jaws are opened far enough to allow the bit tang to
pass entirely within so that the ends of the jaws shall grip the round
part--the shank of the bit. Still firmly holding the brace, revolve
the crank in the opposite direction until the bit is firmly held. Fig.
74.
=37. Center Bit.=--The old fashioned center bit, Fig. 75, is still used
by carpenters for certain kinds of work. It has, for the most part,
given way to the more modern auger bit.
[Illustration: FIG. 75.]
=38. The Auger Bit.=--The auger bit, Fig. 76, is used for all ordinary
boring in wood. The action of an auger bit is readily understood by
referring to Fig. 76. The spur draws the bit into the wood. The two
nibs cut the fibers, after which the lips remove the waste, later to be
passed along the twist to the surface.
[Illustration: FIG. 76.]
Auger bits are usually supplied in sets of thirteen, in sizes varying
from one-fourth of an inch to one inch, by sixteenths.
The size of hole that an auger bit will bore can be told by looking
at the number on the tang or shank. If a single number, it is the
numerator of a fraction whose denominator is sixteen, the fraction
referring to the diameter of the hole which the bit will bore.
Exercise care in laying down a bit; it is easily dulled. Do not use a
good auger bit where there is any danger of its striking nails or other
metal.
Auger bits are easily sharpened, a small file being used, but they are
more easily spoiled by improper filing, and no student should attempt
to sharpen one without having personal direction from his instructor.
=39. The Drill Bit; The Gimlet Bit.=--The drill bit, Fig. 77, is quite
hard and may be used for boring in metal as well as wood. It is easily
broken and especial care must be taken to hold the brace firmly. Do not
try to change the direction of the boring by inclining the brace after
the bit has started into the wood.
[Illustration: FIG. 77.]
[Illustration: FIG. 78.]
[Illustration: FIG. 79.]
In boring hard wood or metal, make a “seat” for the point with an awl
or, in metal with a center punch. Otherwise it is difficult to start
the bit in the exact place.
The gimlet bit, Fig. 78, is used mainly for boring holes for screws.
=40. Countersink Bit.=--Fig. 79 is an illustration of a rosehead
countersink. This tool is used for enlarging screw holes made with the
gimlet so that the heads of the screws may sink into the wood even with
or below the surface.
=41. The Screw-driver Bit.=--The screwdriver bit, Fig. 80, is not a
boring tool, but as it is used in connection with the brace it is
inserted here. It will be found convenient where large screws are to
be inserted. Where a large number of screws are to be inserted it will
permit of very rapid work.
[Illustration: FIG. 80.]
In using the screwdriver bit, especially in driving screws into hard
wood, the bit will tend to jump out of the groove in the head of the
screw. To avoid its jumping entirely out and marring the wood, take
but half a revolution at a time, then move the brace backward slightly
before proceeding again. This allows the bit which has partly worked
its way out of the groove to drop back again.
The manner in which a screwdriver bit is sharpened has much to do with
its working properly. It should be sharpened like the screwdriver.
=42. The Brad-awl.=--The brad-awl is used for boring very small holes.
Unlike most boring tools it does not remove the material from the
opening it makes.
[Illustration: FIG. 81.]
The cutting edge of the brad awl should be placed across the grain in
starting, and the tool turned half way around and back again, repeating
until the proper depth has been bored. It is withdrawn with similar
turnings. Fig. 81.
Patent spiral screwdrivers and automatic drills have come into quite
common use in recent years. They are used mainly upon light work; their
advantage being the rapidity with which they do their work.
=43. Positions while Boring.=--Fig. 82 illustrates the position to be
taken in horizontal boring. The head of the brace is held steady by
bracing the body against the hand which holds it.
[Illustration: FIG. 82.]
[Illustration: FIG. 83.]
To tell whether a bit is boring a hole in the direction which is
wanted, it is necessary to sight the bit and brace from two directions
at right angles to each other. In horizontal boring, the first sight
should be made while in the position shown in the illustration. The
second position for sighting would be obtained by inclining the upper
part of the body until the eye is on a level with the bit. In vertical
boring, Fig. 83, the sighting of the bit would be done across the
piece, then along it.
Changing from one position to the other can be done easily and without
interfering with the boring and should be done quite often, until the
bit has entered well within the wood.
Fig. 84 illustrates a position which is frequently taken when boring in
hard wood, or when using the screwdriver bit on large screws. The chin,
resting upon the left hand, steadies the tool in the first case, and
can be made to give additional pressure in the second.
[Illustration: FIG. 84.]
=44. Thru Boring.=--To avoid splitting the wood around the edge of the
hole when it is desired to make a hole entirely thru a piece, bore from
the face side until the point of the spur can be felt on the back. Then
reverse the position of the board and, inserting the point of the spur
in the hole just made, finish the boring from the back side. The bit
must be held perpendicular to the surface while boring from the second
side, as well as the first, or some of the edge of the hole will be
broken from the first side as the bit is forced thru.
=45. Boring to Depth.=--When it is desired to bore to a given depth,
turn the crank of the brace until the lips of the auger are just ready
to cut the surface. With the rule, measure the distance from the
surface of the piece to the grip of the brace. Fig. 85. The brace may
then be turned until this distance is diminished by the amount which
represents the desired depth of the hole.
[Illustration: FIG. 85.]
[Illustration: FIG. 86.]
Where many holes of the same depth are to be bored much time will be
saved by cutting a block the length of the exposed part of the bit when
the hole is to the required depth. This can be placed beside the bit so
that the grip will strike it. Fig. 86.