Chisels are also classified according to the work for which they are designed: paring, firmer, and framing chisels.
The paring chisel has a thin blade, with the cutting edge formed by a bevel ground at an angle of 15 degrees. It is used for light, fine work and should be used without the aid of a mallet or other heavy driving tool.
The firmer chisel has a heavier blade than a paring chisel, and its angle is 20 degrees. This chisel is used for both heavy and light work; and a mallet may be used to drive it.
The framing chisel has a thicker blade than the firmer chisel. Its bevel is ground at an angle of 25 degrees, and it is used for rough carpentry work.
Chisels are sized according to the width of the blade; they range in sizes from 1/8” to 2". A ½” chisel has a blade or cutting edge ½” wide.
Paring with a chisel
The grain of the wood must be taken into account when paring with a chisel. If paring is done against the grain, the chisel will have a tendency to follow the grain, digging into the wood and splitting it. If the direction of the grain is not definitely known, make a thin trial cut to see if the chisel digs into the grain.
This hand controls the forward movement of the chisel. The force that drives the chisel is exerted by the other hand, which is placed on the handle. The depth of cut taken by the chisel is controlled by raising or lowering the handle. Light cuts should be made with a paring chisel. If it is necessary to remove much wood, make a series of fine cuts.
To make a recess with a chisel, drive it with a mallet. Make a series of small cuts across the grain, holding the chisel at right angles to the surface. After making the vertical cuts, remove the chips by the paring method previously described, working with the bevel side of the chisel down.
The cold chisel
The metalworker may use a chisel for chipping, grooving, or for shearing. The cold or flat chisel is used for chipping and sometimes for shearing off metal. In shearing, the metal is first clamped in the vise. The chisel is then held so that its bevel rests on the jaw of the vise and its cutting edge touches the metal at an angle of about 45 degrees. When the chisel is struck, it acts like one scissor blade while the rear jaw of the vise takes the place of the other blade. Metal can be easily cut this way.
In chipping, the chisel is held similarly, but the bevel rests on the surface being cut, blows are sharper, and goggles are worn for protection against flying chips. Figure 1-46 shows the flat chisel and its two companions, the diamond-point chisel and the cape chisel. The V-chisel is not shown, but it is similar to the diamond-point except that its face, instead of being diamond shaped, is curved to form a V. It is used for grooving.
The diamond-point chisel is used to cut a V-shaped groove. .It can be used to open a crack in a casting in preparation for welding. Sometimes, when a part is to be taken off a casting, instead of sawing it off it is grooved with a diamond-point chisel and then broken off with a hammer or sledge blow.
The cape chisel
The cape chisel is used for cutting rectangular grooves such as keyways. Its cutting edge is made wider than the stock immediately behind it to give clearance to the edge. Without this clearance it would bind in the groove as it cut.
Sharpening a chisel
The grinding and whetting of a chisel is done in the same manner as for the plane iron. Keep in mind that the angle of the bevel differs in some cases from those of the plane iron. The whetting angle of a chisel is 5 degrees more than that of the bevel angle.
Safety in using the chisel. The chisel is one of the most dangerous hand tools that the worker uses, and care must be taken to follow certain rules of safety. When using a chisel keep both hands on it and keep the fingers away from the cutting edge of the blade.
Make certain that the material to be cut is held securely in the vise or held by means of a hand screw or C-clamp to the top of the bench. Never begin a chisel operation until the stock is secure. If it is necessary to remove a piece of stock from the vise or to remove a clamp that is holding the stock, put the chisel down on the bench.
The only time a chisel should be held with one hand is when a mallet is used to drive it. When cutting with a chisel always cut away from yourself. If you carry a chisel around the shop, keep the cutting edge down so that no one walks into it. If these precautions are followed, there will be little danger of a person's being cut by a chisel.