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. 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.
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.
Auger bits are usually supplied in sets of thirteen, in sizes varying from one-fourth of an inch to one inch, by sixteenths. Drill bits vary by thirty-seconds.
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 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.
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. Diameters vary by thirty-seconds of an inch.
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 Screwdriver 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 very rapid work.
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. .—The brad-awl is used for boring very small holes. Unlike most boring tools it does not emove the material from the opening it makes.
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.
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.
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.
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.
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.
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; or a hole may be bored thru the block, the block being allowed to remain on the bit.