46. Chisels.—Chisels are usually divided into two classes, the framing chisel, which is heavy and strong, and the firmer chisel, which is lighter. The framing chisel, Fig. 87 A, is used on heavy work such as the frames of buildings. Its handle is usually fitted into a socket and the top is tipped with leather or banded with iron to prevent its splitting when pounded with the mallet. The firmer chisel, Fig. 87B, is used for lighter work without the mallet, such as paring, and its handle is usually fitted upon a tang.
The mallet, Fig. 88, should always be used for driving chisels, gouges, pins, etc. Its blow is not so concentrated as that of the hammer and therefore not so likely to injure the chisel handle. It should never be used for driving nails—wood for pounding wood, metal for pounding metal, is a good rule to follow.
The size of a chisel is indicated by the width of the cutting edge and varies from one-eighth of an inch to two inches.
To do good work a chisel must be kept very sharp, and special care must be taken in handling it. Both hands should, at all times, be kept back of the cutting edge.
The action of a chisel driven into the wood with a mallet is somewhat similar to that of a wedge. This must be taken into account when cutting dadoes, mortises, etc., where it is desired to cut away the waste exactly to a given line. If the chisel were beveled on two sides the action would be the same as that of a wedge; that is, the wood would be pushed to either side equally.
Since the bevel is on one side only, beginners are prone to think that the wedging takes place on one side only, the bevel side. Most of the wedging does take place on the wood at the bevel side, but there is enough pressure against the bevel to force the flat side of the chisel over the line slightly onto the part which it is not desired to cut. To overcome this action, chisel a line parallel to the given line, about one-sixteenth of an inch away from it, on the waste. When the opening has been cut to depth, the chisel may be set exactly in the given line and driven to depth. The narrow margin of waste wood breaks off; the pressure against the bevel is therefore almost nothing. Fig. 89.
47. Horizontal Paring Across the Grain.—In horizontal chiseling
the work should be fastened so as to leave both hands free to guide the chisel.
Fig. 90 shows the manner of holding the chisel. The left hand rests against the piece of wood and the chisel is kept from cutting too far by the pressure of the thumb and fingers of this hand. With the bevel side of the blade up, move the handle from right to left carefully while pushing it forward; pare off pieces about one-sixteenth of an inch thick half way across from edge to edge. Fig. 91. When within a thirty-second of an inch from the gage line hold the chisel so that its cutting edge shall move obliquely across the grain and pare just to the gage line. The direction of the grain will determine which corner of the chisel is to cut ahead. In starting the last cut place the chisel squarely in the gage line. The piece should be reversed and the cut finished by cutting in a similar manner from the second side.
Fig. 92 illustrates a second method of horizontal paring. It differs from the first in that the chisel is turned while in the horizontal position so that one of the edges is free of the wood. By cutting first with one edge free, then the other, the surface may be lowered until only a low ridge extends across the piece from edge to edge. This ridge may then be removed by cutting to the gage line in the usual manner.
If the chisel is properly sharpened the surface may be left as. smooth and as level as if planed.
48. Vertical Paring.—In vertical paring hold the chisel as shown in Fig. 93. The left hand resting upon the wood holds the wood in place, while the index finger and thumb of the left hand assist in placing and guiding the chisel. Only a small portion of the cutting edge can be used in vertical paring; the amount will depend upon the hardness of the wood and the strength of the student. Ordinarily, not more than one-quarter of an inch of the chisel width can be used for Fig. 93. very soft woods and not more than one-eighth for hard woods.
That part of the blade which is not used for cutting purposes is used as a guide to insure each cut being in the same plane as the last. The chisel should be inclined toward the worker, the unused part of the blade pressed firmly against the part of the surface already cut. To make the cut, apply the needed pressure, at the same time moving the handle forward until the chisel shall have a vertical position as shown by Fig. 94. the dotted lines in Fig. 94. Care must be taken to keep the broad surface of the chisel at right angles to the surface of the work at all times. The worker should so stand that he may look along the line as he cuts it. Otherwise he is in no position for sighting the chisel plumb.
49. Oblique and Curved Line Paring.—Whether cutting with the grain or across the grain, care must be taken in oblique and curved line paring to cut from the straight grain toward the end grain.
50. Paring Chamfers.—Fig. 96 illustrates two ways of holding the chisel in cutting chamfers. In one, the bevel side of the chisel is down and the cutting edge held at right angles to the grain. In the other, the flat side of the chisel is down and the cutting edge is worked oblique ly to the grain.
Frequently it is desired to chamfer or bevel the end of a piece of wood with the chisel. To do this hold the cutting edge obliquely to the grain, the flat side f the chisel down. Fig. 97. The use of the framing chisel is described in connection with the making of the mortise.
51. The Firmer Gouge.—Fig. 98. The gouge is curved in section and may have its bevel on either side. It is used for cutting grooves and hollowing out surfaces. The size of the gouge is determined by measuring the straight distance between the corners of the cutting edge.
When roughing out where rather thick shavings be taken, the gouge should be held as in Fig. 99, the blade being held firmly in the left hand. When taking off thin shavings and in finishing, the tool should be held as shown in Fig. 100. In using the gouge avoid short strokes. Try to take as long and as even shavings as the nature of the work and the wood will allow. The thinner the shaving, the easier it will be to cut smoothly. A circular movement imparted to the cutting edge will en able the tool to cut more easily the end grain of ood, as is necessary in cutting the ends of grooves in pen-trays, etc.
52. Grinding Beveled Edge Tools.—When edged tools become rounded over by repeated whettings or when they are nicked too deeply for the oilstone to remove the nicks, the grindstone is needed to cut the metal to the proper angle. Fig. 101 shows the manner of holding the chisel upon the stone. The tool must be held firmly and at the same angle. This angle will depend upon the temper of the tool and the kind of wood to be cut, whether hard or soft, soft wood allowing the use of a sharper angle. On plane-irons the length of bevel, or grind should be three-sixteenths or one-fourth of an inch; on the chisels, three-eights or one-half an inch.
The tool should not be kept in the middle of the stone but should be moved from right to left and vice versa across it as the grinding proceeds, that the surface of the stone may be worn as evenly as possible. The pressure of the left hand should be so applied that the stone shall cut straight across the blade. Examine the tool often, being careful to replace it each time as nearly as possible at the same angle. Fig. 102 shows the fiat bevel which is to be obtained, also the rounded effect caused by frequent changing of the angle at which the tool is held. Grindstones are usually turned towards the tool because in doing so they will cut faster.
Water is caused to flow on the stone for two reasons: To keep the edge of the tool from being burned or softened by the heat which friction would generate, and to wash off the particles of steel and stone, thus keeping the cutting surface clean that it may cut the more freely.
53.Whetting Beveled Edge Tools.—The grind stone does not harpen tools; that is the work of the oil tone. No tool, after it has been ground, is ready for use until it has been whetted.
54.Oilstones.—Oilstones in common use are of two kinds; those which are of very fine-grained natural stone and those which are manufactured by pressing a powder ed, metal cutting substance into rectangular forms. In selecting an oilstone it should be remembered that the finer the grain the keener the edge it will produce but the longer time it takes to produce it.
Manufactured stones are frequently made "two in one," that is, coarse and medium or medium and fine are put together in such a way that one side gives a rapid cutting and the other a slower but smoother cutting surface. The advantage of such a stone is easily understood.
Oil is used on stones to cleanse the pores of the stone of the little particles of steel cut from the tool. Were it not for the oil mixing with and removing these particles the surface of the stone would soon become smooth and friction so reduced that the cutting power would be greatly interfered with.
While but a part of the stone need be used at one placing of the tool, effort should be made to utilize as much of the surface as possible that the surface may be kept level as long as possible. Stones that have worn uneven may have their surfaces leveled by rubbing them on a piece of sandpaper or emery paper placed on a flat surface.
55. Sharpening the Chisel.—Hold the tool as shown in Fig. 103. Suppose the grinding produced a bevel of about twenty-five degrees, in whetting effort should be made to hold the blade so as to produce an angle slightly greater than this. The amount shown in Fig. 107 a and b is exaggerated. The aim at all times should be to keep this second angle as near like the first as is possible and still get a straight bevel to the cutting edge.
To get the tool into proper position, lay it flat on the stone with the beveled edge resting in the oil which has previously been placed on the stone. The oil should be drawn to the place where the whetting is to be done, the back edge of the bevel being used to push and draw it to place. Gradually raise the handle of the tool until the oil is expelled from under the cutting edge; it is then in position. Use just enough oil to keep the surface well moistened where the whetting is being done.
Rub the chisel back and forth, keeping it at the same angle all the time. A rocking motion and frequent change of angle will result in a rounded end instead of a straight bevel. Some workmen prefer to give the blade a circular instead of the forward and backward movement.
To remove the feather or wire edge which frequently results from over-whetting or from grinding, proceed as follows: Hold the tool with the flat side down, just a little above the stone, with the handle just a very little higher than the cutting edge. In one stroke push the cutting edge forward and down on the stone, at the same time lowering the rear end to a level with the cutting edge. The effect of this movement is to turn the wire edge under and cut it off. If the first attempt does not remove it, whet the bevel just enough to turn the edge back on the flat side and try again. The presence of a feather edge is detected by rubbing the fingers along the flat side over the cutting edge.
If a still keener edge is desired it m y be obtained by the use of
a strop, a piece of leather fastened to a flat surface. Hold the tool as shown in Fig. 104 and draw it toward you several times. Then hold it with the flat side down and draw it back once or twice.
The angles of the bevels of a gouge are similar to those of a chisel. In sharpening, hold the tool at right angles to the edge of the stone, instead of parallel as with the chisel. Move it lengthwise of the stone, at the same time rotating the handle so as to give the blade a circular motion as from A to B, Fig. 105.
The feather edge which is formed on the inside is removed by a few strokes of a stone called a slip. Hold the slip firmly against the face so as not to form a bevel. Slips are of various sizes; one that fits the curvature of the gouge should be selected.
56. Sharpening Plane-irons.—Plane-irons are sharpened straight across like the chisel, with the exception of the jack-plane, as previously noted. Their corners, how ever, are very slightly rounded off to prevent their leaving marks on the wood. Where one plane is made to serve the purpose of smooth, jack and fore-plane, it should be ground straight across. In whetting, increase the pres sure on the edges alternately so as to turn up a heavier feather edge there than in the middle, thus rounding the whole end very slightly. This feather edge may be removed in the usual manner.
57.To Tell Whether a Tool is Sharp or Not.— Examine the cutting edge, holding the tool toward the light. If the tool is dull, the cutting edge will appear as a white line, the broader the line the blunter the edge. Fig. 107A. If the tool is sharp, no white line can be seen. Fig. 107B. (See page 64.)
A better way—the method a mechanic would use—is to test the edge by drawing the thumb along it lightly.
Fig. 108. If the tool is sharp one can feel the edge "taking hold." If dull, the thumb will slide along the edge as it would along the back of a knife blade.
Good judgment is necessary in this test or a cut on the thumb may be the result. No pressure is required, just a touch along the edge at various points
What actually takes place is this: The cutting edge, if sharp, cuts the outer layer, the callous part of the ball of the thumb, just a little. The sense of feeling is so keen that the resulting friction, slight as it is, is transferred to the brain of the worker long before any injury need be done the thumb. If the tool is dull, no cut, hence no friction can result. Do not use the finger, as it is not calloused as is the thumb.