This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Forms of chisels and gouges are shown in the annexed illustrations. The difference between a chisel and a gouge is that the former has a straight cutting edge while the latter is more or less curved. Fig. 343 is a common paring chisel; Fig. 344, a socket mortice chisel; Fig. 345, a common mortice chisel; Fig. 346, a thin paring chisel with bevelled edges; Fig. 347, a common gouge in its handle; Fig. 348, a long thin paring gouge, cannelled inside. Mortice chisels range in width from i in. to 1 in., the sizes increasing 1/16 in. at a time; paring chisels advance 1/8 in. at a time, from 1/8 in. to 2 in. wide; gouges have a similar range, in addition to which they are made with 8 different degrees of curve, as shown in Fig. 349, and known respectively as A or very flat, B or flat, C, D or middle, E, F or scribing, G or half fluting, H or fluting. In the figure, all are 1-in. size.
The chisel cannot be used satisfactorily over a surface wider than itself, and though the gouge was devised to excel it in this respect, there is still a tendency for this tool to follow the leadings of the fibres of the wood rather than cut through them at a very slight obliquity. The only guidance the tool receives is from the hand of the workman, hence everything depends upon the degree of his skill. The impossibility of ensuring the amount and direction of the cut given by the chisel was the main incentive to introducing its modified forms the spokeshave and the plane, which will be discussed presently. In paring, the chisel is held in the right hand and applied with a thrusting motion without the aid of a mallet, the left hand being employed to hold the wood, and always kept well in rear of the tool to avoid accidents in case of the tool slipping. The wood to be operated upon should be held securely and in such a manner that if the tool goes beyond it or misses a cut it will neither damage its own edge nor meet with anything that will be injured by it, such as the surface of the bench.
In paring horizontally or lengthwise with the fibres of the wood, the forefinger should be extended along the tang of the tool; but in paring vertically across the grain, all the fingers should firmly grasp the handle. When cutting mortices and tenons, the chisel is tightly held in the left hand while the right wields the mallet for giving effect to the cutting tool. To make a close joint, it is very necessary that the edges cut by the chisel (as well as those cut by the saw) shall i e perfectly square and flat. This can only be attained by observing the correct way of applying the chisel-edge to the work. If the flat side of the chisel be held against the shoulder that is to be cut away, the chisel will " draw in "; if the bevelled side is against the shoulder, the contrary effect will be obtained. This is illustrated in Fig. 350. If the chisel is held as at b or d, just (and barely) allowed to cut, it will act as a paring tool; but its tendency will be found to follow the dotted line b c, so that, if not checked, it will "undercut" the shoulder. When held as at a, its tendency is in the opposite direction, when the sloping end can be rectified without spoiling the work.
The same care is needed in cutting a mortice (Fig. 351). Let the mortice be carefully marked on both sides, but cut right through from one side only; the chances are that it will be found to have been cut too long on the farther side of the stuff from the drawing in of the chisel. The section will be as at a, Fig. 351. Of course, therefore, the safe plan when a mortice must be cut only from one side is to cut it more like b, and to pare it back carefully at the finish. Whenever possible, however, a mortice should be cut from both sides - half through from each; but the same tendency of course prevails, the result being shown in c, and here the faulty work will not be visible in the least when the tenon is in its place. The joint will appear quite close-fitting and neat, but it is evident that it will have little strength, as the component parts are only in contact just at the 2 surfaces, the rest being quite hollow. The best way to begin a mortice is shown at d. It should he commenced by cutting out wedge-shaped chips from the middle, cutting each side by turns, and it will he found in many cases easier to take out the main part of the chips with the bevcl of the chisel downwards.
Each chip is thus heaved by pressing on the bevel as the fulcrum, and the mortice is gradually lengthened each way. After the main part of the wood has been removed, the back of the chisel is used next the shoulders, as already stated, care being taken, as the work approaches completion, that the hole is not undercut, but that the mortice when finished shall have 4 perfectly flat walls, the sides as free as possible from loose fibre.
Another cause of failure in making a clean tight joint is the bruising of the fibres on the surface of the board at the end of the mortice by using a blunt chisel. It is mainly avoided by commencing in the middle, as just explained, and using a keen chisel to finish with. Certainly the work may be passed over again after the mortice is cut, but this is not always allowed for in squaring up the piece originally. In soft wood, especially when the fibres are loosely compacted, they will bruise and start up considerably if struck with a blunt tool, and often come completely away, leaving a depression that cannot be effaced without deeply planing the surface. Stray tacks, chips, and inequalities in the surface of the bench will also produce had results.
The gouge is used and held in the same way as a paring chisel. When driven by a mallet it should always have a perpendicular position.