The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking. Paul N. Hasluck
as chair-seat frames, circular rims for loo tables, and other circular work built up in segments, and the methods described also apply equally well to oval, semicircular, and other curved work. One method of closing with straight bar cramps is to provide projecting cramping pieces A (Fig. 121). This is done when setting out the stuff, the cramp jaws embracing one cramping piece at each side of the leg, and the seat frame being dressed up afterwards. This method, however, entails a great waste of wood, and in marking out circular work it is of great economy to mark one piece with the other, which cannot be done with the method described above. Where the curved members act as stuffing rails to be covered by the upholstery, another method is to cut a piece out of the rails as shown at B, the cramp jaws in this case fitting in the notches, which are afterwards filled up by the pieces of wood being glued in again. But this method makes the frames very unsightly. The flexible cramp shown applied externally to a circular seat at Fig. 122 consists simply of a pair of beech-wood horns (Figs. 123 and 124) about 8 in. long by 2 in. thick, to which a narrow band of hoop iron is attached by means of screws or rivets. This hoop passes round the seat frame, and pressure is brought to bear on the horns by a hand cramp or by an ordinary bar cramp. The cost of these cramps is small, and a variety of sizes will be found exceedingly useful. Another flexible cramp is shown at Fig. 125, the horns in this case being replaced by rectangular pieces of hardwood. The cramp is shown as applied to a curved couch end, the pressure being applied by a bar cramp at each side. This kind of cramp is useful for semicircular work, such as bow-front chairs, curved pediments, bell-shaped backs, etc. Fig. 126 illustrates a flexible cramp which is self-contained, the hoop iron band being riveted to steel or brass ends, which are threaded (see Fig. 127) to receive winged nuts. They pass through a stiff bar of hardwood, which keeps them in position, the cramping being done by tightening up the nuts. This kind of cramp applies to almost any kind of irregularly shaped work.
Fig. 125.—Flexible Cramp.
Fig. 126.—Screw-end Flexible Cramp.
Fig. 127.—Screw of Flexible Cramp.
Fig. 128.—Lancashire Pincers.
PINCERS.
Pincers are very familiar tools used for extracting and beheading nails, and for other purposes where a form of hand vice is wanted for momentary use. There is but little variety in their shape, and they range in size from 5 in. to 9 in. Usually one handle ends in a small cone (see Fig. 128) or ball (see Fig. 129), and the other in a claw for levering out nails, etc. Fig. 128 shows Lancashire pincers, and Fig. 129 Tower pincers.
Fig. 129.—Tower Pincers.
PARING AND SHAVING TOOLS.
THE ACTION OF A PARING CHISEL.
BEFORE describing edge tools and their uses, it will be well to discuss the action of such typical tools as the chisel and knife; though the latter is not generally found amongst woodworkers’ ordinary tools. It is desirable to examine the manner in which the power applied to a chisel is used, and for simplicity’s sake it is better to conceive the cut as being made upon some homogeneous material, such as lead. Taking first the ordinary method of paring, in which the face of the chisel is in contact with the mass of the material, Fig. 130 shows the force A that impels the chisel; B is the resistance of the material to the crushing action of the edge of the chisel; C is the reaction of the paring to the pressure exerted by the bevel of the chisel; and D is the reaction of the body of the material to the pressure exerted to the face of the chisel. To obtain a proper conception of the actual cutting edge, it must be borne in mind that the edge of even so delicately sharpened a blade as a razor presents a jagged, rough appearance when viewed through a microscope, and theoretical or mathematical conception of an edge is never attained in practice. It is the greater or less approximation to it—or, in other words, the sharpness or bluntness of the chisel—that determines the amount of the force B (Fig. 130). The passage of a thin parallel blade with a square edge through, say, a bar of soap is obtained entirely by the crushing and displacement of the material, and the thinner the blade the less the resistance, and therefore the smaller the force required. The edge of the chisel must be regarded as such a blade of exceeding thinness; but to allow the passage of the chisel blade, which has considerable thickness, the paring must be bent aside as it advances. In setting out the force B, the frictional resistance to the advance of the chisel may be included. In its resistance to being bent aside, the paring acts as a very short cantilever; so it is evident that the bending force which produces the reaction C increases rapidly as the paring becomes thicker.
Fig. 130.—Direct Paring with Chisel.
ANGLES OF CUTTING EDGES.
Whatever the amount of the force required to bend the paring, it is clear that the smaller the angle at which the chisel is sharpened the smaller will be the horizontal component f (Fig. 130), and, consequently, the smaller will be the thrust required to make the cut. This shows the advantage of sharpening at a small angle; for, if the angle be greater than is necessary, the extra force required is wasted in bending the paring to a sharper curve. To avoid complication, the sharpening of the chisel is shown as one bevel, instead of the two produced by the successive actions of grindstone and oilstone (see p. 39). When the oilstone bevel is very small, the reaction C may be regarded as taking place (in cutting wood, at any rate) between the grindstone bevel and the paring; but when the oilstone bevel is very wide, reaction takes place chiefly between the latter bevel and the paring; and since it has a greater angle than the grindstone bevel, more force is required in using the chisel. Hence it is desirable to grind the chisel frequently.
Fig. 131.—Inclined Paring with Chisel.
ROUGHNESS OF CUT SURFACES.
Sometimes in cutting wood the surface left is found to be extremely rough, even though the chisel