Cold chisels

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Fig. 1 - The more common types of cold chisels used in metalwork: the flat, crosscut or cape, round-nose or half-round, and diamond-pointed chisels. Chisels can be sharpened by grinding.

Fig 2. How to hold a flat chisel when cutting sheet metal. Note that the chisel is held at an angle so that when struck by the hammer it moves towards the worker. A piece of soft iron should be placed under the sheet metal when cutting.

Cold chisels are used for cutting heavy metal that cannot be sawed with a hacksaw or cut with shears. Cold, chisels are made from carbon tool steel, usually of octagonal section. They are heated and hammered to the desired shape and finished more accurately by grinding. Next, they are hardened and tempered, and sharpened. according to the particular job for which they are intended. Fig. 1 shows the four kinds of chisels in common use. The flat chisel is most widely used and has a place in every home workshop or tool kit. It has a broad cutting edge which should be slightly rounded to reduce the tendency of the corners to dig in. This chisel can be used for cutting off rods, cutting out sheet metal and other jobs of this sort.

For cutting sheet metal, the chisel must be held at a slight angle to the surface of the metal, as shown in Fig. 2. This is done so that when the chisel is struck by the hammer it tends to move along the ' line continuously toward the worker, at the same time aa it cuts through the metal. If the chisel is held vertically, a separate cut is made each time the chisel is struck by the hammer, and the "line" then becomes a series of short cuts. A block of soft iron is generally used for support.

Fig. 3 - Care is needed to prevent the edge of a sheet from being distorted when cutting out slots. This can be avoided by drilling a series of holes as near together as possible. The lower figure shows a plate drilled in this manner.

Fig. 4 - When cutting sheet metal held in a vise, have the line to be cut as near the top of the vise, jaws as possible. This will prevent the metal from bending.

Chiseling Sheet Metal. The same method of cutting is applied to making slots of various shapes and sizes in sheet metal, although the removal of the metal can be simplified by drilling a series of holes as near together as possible before using the chisel. This should always be done where the amount of metal left on the outside of the slot is small; otherwise, the chisel would distort: the shape of the plate (Fig. 3).

As shown in Fig. 4, when cutting metal held in a vise, care must be taken that the line to be cut is as near the top of the vise-jaws as possible, so that the metal is not bent or the edge of the cut badly burred.

Types of Chisels. Cold chisels are used for any number of repair jobs, such as cutting off rivet heads, cutting through nuts and bolts which have rusted fast, and other heavy work. The crosscut or cape chisel is forged in such a fashion that the cutting edge is slightly wider than the body; this is to ensure that the chisel does not bind in the cut when it is used for deep grooves. A round-nose or half-round chisel is used for special work, such as forming flutes and channels. The diamond pointed chisel is drawn down to a square section at the end and then ground away to a single bevel. It is used for chipping through plates and cleaning out square internal angles.

Sharpening. All the chisels described are usually sharpened by grinding, preferably on a wet grindstone. After frequent regrinding, however, the cutting edge becomes too thick, and the chisel then has to be heated, drawn down to shape, and retempered. The correct thickness of the edge will vary according to the kind of metal that is to be cut; the softer the metal the thinner the edge of the chisel may be.

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