ROBERT GIBSON GRISWOLD

In our first chapter we considered briefly the forging of a set of light hand tools, and in this chapter we will extend this set to that of a series of cold chisels of various sizes and shapes, 6uch as will be most useful and convenient for the work generally pursued by the amateur.

A good working set of cold chisels should comprise quite a number, for they bear the same relation to work in metals as the carpenter's chisel does to woodwork, and for the same reason that a variety of shapes and Bizes of the latter tools prove expeditious in work, so will a variety of cold chisels prove very useful in all classes of work in metals.

The steel of which cold chisels are generally made is special and octagonal in shape. This octagonal shape is convenient in forming a grip for the hand to prevent twisting when struck with the hammer. When the steel is purchased at the jobbers they can give information as to the grades, which are so great in number and constantly changing that it would hardly be possible in this article to describe them. Old flies make excellent chisels when properly treated, and they stand up to their work admirably.

The character of the work determines largely the width of the cutting edge, and for this reason a number of cutting sizes will prove acceptable. When cutting hard metals, such as cast iron and steel, heavy blows must generally be struck, and a narrow chisel would not stand it long without cracking on the edge, while with the softer petals, such as copper, brass and babbitt, lighter blows should be struck to prevent the metal breaking and crumbling before the chisel, this rendering the cut rough and uneven, and narrower tools are generally used for this work. But even the above rule cannot always be used for more than a guide. The thickness of the cutting edge and its angle play equally important parts, as will be spoken of later on, and the experience and judgment of the workman must be relied upon to some extent.

In Fig. 1 is shown a number of chisels shown by a, b and c in the form most commonly used for general work. The head should be forged down as shown so that " brooming " will to some extent be prevented. A very convenient length is five inches from head to edge, with a gradual taper from the body to the edge, as illustrated. The cutting edge is ground to about 60°, although it ranges from 45° to 75°, the blunt angles being given to the tool when used on heavy work. The flat chisels should be made in a set as follows: 3/8 in. i in., 5/8 in., and 1 in. in width.

When the tool is forged the edge only must be hardened for about 1/8 in., the metal above being left softer to withstand the shock. When the tool is left hard too far up a heayy blow will cause the thin point or edge to crack off on a line, as shown by the dotted line on b. Draw the temper to a light purple for steel and a dark purple for cast iron and wrought iron work.

A set of gouges as shown by d and e should be made in the following sizes, 1/4 in., # in., $ in. and £ in. The bevel is ground on the concave side and flat on the convex side. The gouges are used for cutting grooves and fillets.

A chisel made as in f and g is very useful and is called a side chisel. The edge of the chisel coincides with a flat side, thus enabling thin paring chips to be taken from the inside of a slot or square hole, which could not be done very well with the ordinary flat chisel. These chisels should be made in three sizes, i in., 3/8 in., 1/2 in.

The chisels shown in h, i and j are known as the cape chisels and are used for cutting grooves. The point is made the width of the groove and the stock behind is made slightly thinner to give clearance. Two sizes, 3-16 in. and 1/4 in. are sufficient. The shape ; is very handy in cutting the ends of key way6 square. It is practically the same as a 1/4 side chisel of form f but it is much stronger.

The diamond point chisel k and I is used for cutting sharp corners, V grooves and lettering. Only one size is necessary, the side of the 6quare being about 1/8 in. It should not be ground to too keen a point, as it is easily broken when not well supported. When a diamond point is bent as in m it can be readily used on a flat surface.

Two round-nose chisels are shown at n, o, p and q. The form n is used for heavy work, and 1/8 in. and 1/4 in.

are sufficient. The form p is lighter and is used as a drawing chisel for drawing a drill when it runs out of true. It is simply a round-nose chisel with a very long taper and small radius.

It is often necessary in fine work to remove only a very thin chip. If the ordinary flat chisel is used the corners will leave ugly cuts on the surface. The chisel is then ground slightly as in r, which keeps the corners in sight at all times, and very thin chips can be taken.

The form s, t is useful in cutting keyways in small holes, as the body of the chisel is kept away from the work and clean cuts can be made. The forms u and v show a caulking tool with a round nose, and at w is a tool with a serrated face, useful in peening out small surfaces, heads of rivets, etc., which are too thin to stand heavy peening. The face is provided with teeth by filing diagonal slots before hardening.

The tool v is made for splitting rivets before finally peening flat. It spreads the rivet quickly and requires only a light blow.

If the amateur provides himself with a set of tools he will be in a position to work quickly and expeditiously and the work need not suffer for want of the proper tools. Our next installment will treat of a 6et of lathe tools.

There are several photographic methods of making lantern slides of drawings and diagrams, of which the wet-plate process is, perhaps, the best; but recently it occurred to me to try a simple method, which has given most satisfactory results, though I do not remember to have seen it suggested elsewhere. All that is necessary is to draw or write with a hard pencil - a 6 H for choice - on ground glass squares 3 1/4x3 a1/4, of as finely ground glass as possible, then to flood the ground side of the glass with dilute Canada balsam in xyol or benzol. Cover with an ordinary lantern-slide covering glass, and bind in the usual way. The glasses must, of course, be first carefully cleaned. The result will be that the ground glass is made transparent while the pencil lines become more distinct. - F. S. Scales.

One result of using very short focus lenses, points out Photography, is that the illumination falls off rapidly as the margin of the plate is approached, a fact that may not be suspected at first, but which will make itself painfully visible as soon as a case occurs when the exposure has been full short. This is partly due to the lens. By measuring the actual proportion of the light falling upon the edges and the centre of the plate respectively, it would be found that while the difference in the quantity of the incident light is considerable, it is less than the difference in its photographic action. Comparatively little of the light that falls upon or near the centre of the plate is lost by reflection ; but as the rays approach the edges, reflection becomes greater, and a very small proportion of them are available for useful work in the plate.