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CHIPPING METAL AND CHIPPING TOOLS

Chipping is a process of removing metal from a workpiece by means of a cutting instrument such as a chisel and a hammer. This process is used when a large piece of metal has to be removed from a workpiece; this process is very labour-consuming' and is applied only in cases when the workpiece cannot be machined. Chipping is used in cases when it is necessary to cut off a piece of metal from sheet metal. Chipping of large parts is always done on an anvil but very of ten it is done in a bench vice. The workpiece to be tooled is fixed during the cutting process in the bench vice.

There are different tools used in metal-working shops for chipping stocks such as chisels. A chisel is a tool made of very hard steel, having a cutting edge at one end of the blade. This cutting edge is wedge-shaped. Under the effect of an external force applied to the wedge it cuts into the metal. The work of the wedge depends mainly on its cutting angle. The cutting edge of the chisel should be sharpened to an acute angle so as to provide for the best cutting ability, depending on the stock to be chipped. The harder the metal, the larger should be the cutting angle of the chisel and vice versa. An angle of about 70 is suitable for most work. Fig. 2 shows a scheme of the process of cutting into metal, and the angles of the wedge. There are different types of chisels such as flat chisels, cape chisels, etc.

Hammers are striking tools used in chipping, bending and other operations. Hammers are made of a solid piece of forged tool carbon steel, their weight depending on the stock to be removed.

. METAL-CUTTING AND LOCKSMITH'S CUTTING TOOLS

Metal cutting differs from chipping in substituting impact stresses by pressing forces in this operation. Cutting is used for separating some part from a piece of

metal as well as to cut angles, grooves and pipes. Depending upon the shape and size of workpieces cutting is done by means of different cutting tools such as pliers, bench-shears, alligator shears, hack saws and pipe-cutters made of carbon steel.

Pliers, or wire-cutters (Fig. 4) are used for cutting thin wire. Pliers consist of two cutting jaws and two handles. A piece of wire is placed between the cutting jaws and the wire is cut by exerting pressure on the handles of the pliers. Bench shears are made of steel. Lateral surfaces of shear blades are hardened, sharpened and ground.

Bench-shears (Fig. 5) are provided with two handles one of which is at a right angle to the other and fixed on a bench. The length of the handle is 400-800 mm, while that of the cutting part is 100-300 mm. The material is cut by pressing on one of the handles.

A hack saw (Fig. 6) is used for cutting thick metal sheets, bars, round-shaped material, etc. The hack saw consists of a frame and a long toothed blade made of tool carbon steel. The teeth on the blade are hardened. The blades with different pitches have different applications, the pitch of the blade depending on the material to be sawed. The thinner the material to be handled, the finer must pitch be the pitch of the blade used for sawing this material, and vice versa.

Fig. 7 shows alligator shears which is a heavy duty machine used for cutting materials of large sections such as pipes, beams, auto frames, axles and different types of industrial scrap. The alligator shears consist of cast iron bed I and bedplate 2. Arm 3 is mounted on the bedplate. Cutting blade 4 is fixed within the arm.

Special pipe-cutters (Fig. 8) serve for cutting pipes. The pipe-cutter consists of body 1, handle 4, and three steel cutting rollers. Two rollers 2 installed on the fixed axles of the body and roller 8 installed on the axle of the handle may revolve and cut a pipe fixed in a special pipe fixture. For this purpose the pipe-cutter is turned round the pipe to be cut, pressing the cutting rollers against its surface.

3. FILING AND FILING TOOLS

Filing is the most widely used fitting operation in the practice of metalworking shops "used for cutting metal by means of a tool known as a file. By means of a file it is possible to give a different shape and size to a workpiece, to fit one part to another, etc.

The most widely used operations with a file are: (1) filing separate surfaces, (2) filing mating surfaces, (3) filing holes.

A file is a hardened steel bar having a great number of fine cutting edges or teeth running diagonally across its face. These teeth can remove fine chips from a treated workpiece. A file differs from a chisel in having a large number of cutting points instead of one cutting edge and in being driven directly by hand instead of by hammer.

There are various kinds of files applied for finishing different workpieces depending on the shape of their surfaces (Fig. 9).

Flat files are used for filing flat surfaces but the shape of the files is not quite flat because if the file had been made quite flat, it would have prevented the

production of a flat surface, as the file would have cut away at the edges of a work and would have left a convex surface.

For filing convex and concave surfaces half-round files are used. A half-round file is made with a convex surface to prevent all the teeth from cutting at the same time, which requires too' much pressure on the file, as well as to prevent the file from bending.

Square files are applied for filing square holes and rectangle grooves, while triangular or three-square files are used for filing angles.

Round files are used for filing round holes of small diameters, and for filing metal in narrow plates diamond shaped files made of copper strip into which diamond powder has been hammered, or knife files are used.

For filing soft metals rasp files or rasps are employed.

4. MECHANICAL TOOLS

Both in maintenance and in repair of machines all kinds of fitting operations are applied. An important role is played by disassembling and assembling operations. Special instruments are used for performing these operations.

Among the variety of mechanical tools used for disassembling and assembling machine parts and in their repairing are wrenches (Fig. 10). According to their construction and application wrenches may be of different types: single-ended and double-ended nut wrenches, adjustable wrenches, socket wrenches and special wrenches.

A nut wrench is used for screwing and unscrewing nuts. It consists of a handle and a head with an opening known as the span.

Adjustable wrenches may be used for unscrewing nuts and bolts of different dimensions.

Socket wrenches are applied in cases when nuts or bolt heads located in recesses are hardly accessible for a nut wrench.

Special wrenches are used for unscrewing and screwing nuts of a definite type.

Wrenches are used by drivers for repairing cars, in locksmith's shops and fitter's shops. Fitters use them to screw different types of machine parts as: washers, bolts, shafts, etc. Plumbers use them to repair pipes, taps, etc. Besides different types of wrenches there are round pliers or needle nose pliers which are widely used by locksmiths, electricians and other specialists for gripping, screwing or cutting off thin metal and wires.

7. DRILLS AND DRILLING

Drilling is one of the cutting operations producing cylindrical holes of different diameter in solid material by means of rotating tools called "drills" (Fig. 22).

The most common type of drill in use1 is the twist drill made of a tempered steel round bar stock. Twist drills are made with two, three, or four spiral grooves or flutes milled from the solid. These grooves or flutes winding around the body of The drill serve for forming the cutting edges of the drill, as well as for removing the chips formed in drilling from the hole.

Straight-Shank Drill

Tapered-Shank Drill

Fig. 22. Drills.

The twist drill comprises three principal parts: body, shank and point. The twist drill has two cutting edges known as the "lips". These cutting edges, or lips, are connected e by a third edge, called a "web". It is this part that gives rigidity and strength to the drill. When in use the first two cutting edges remove the material

from the work, while the third one penetrates into the material by rubbing rather than cutting.

In order to drill holes in a metal the cutting edges of a drill should be correctly ground to a certain angle. When a drill is ground correctly, its cutting edges, or lips, should have equal length whereupon each of them should make the same angle with the centre line. Otherwise the drill will make holes the diameter of which is larger than that of the drill. This may disable the drill and cause an undesirable waste of material. Drills have shanks of various types, the most commonly used being those having straight and tapered shanks. The shank of the drill serves for clamping the drill either in the chuck spindle or socket of a drilling machine. The above part of the drill may be either of a cylindrical shape, like in2straight-shank drills, or of tapered shape in tapered-shank drills.

The third part of the drill is called a "drill point". It is always ground to a cutting angle varying with the kind of material to be drilled. For hard materials this cutting angle equals 140° and for soft materials it equals 90°. The cutting edges of flat drills used for drilling holes in steel or in cast iron are ground to an angle of 100° to 120°. All the drills get worn while drilling and they should be re-ground from time to time.

1. WELDING

Welding is a process which provides a non-detachable joining of two like metal pieces1 by heating them till melting condition or fusion without or with mechanical pressure. Fusion of two metal pieces may be brought about2 by different types of welding, such as hammer welding, thermit welding, electric welding and gas welding.

Hammer welding is a process in which two metal pieces are joined and fused together by force from a hand or power hammer after having heated these pieces in a blacksmith's forge until they reached their plastic stage.

Thermit welding is a process consisting of a chemical reaction obtained by igniting finely divided aluminium and iron oxide. This type of welding is used in repairing rails, frames, etc.

Electric resistance welding is a process consisting of heating metals to be welded to their plastic temperature and then applying mechanical pressure for achieving a non-detachable joining of the metals.

Resistance welding processes form a group consisting of many types of welding. Selection of each type of welding depends on the kind and size of metals to be welded. Resistance welding embraces such processes as spot welding, butt welding, electric arc welding, etc.

Spot welding is a process in which two metals are held between electrodes passing a heavy current through the metals to be welded. The electrodes having been forced together by pressure join the surfaces of the metals in a spot, the size of which is about the same as that of the tip of the electrode. This kind of welding is suitable for welding parts of airplanes, refrigerators and automobiles.

In butt welding the parts to be welded are pressed together while heat is generated by passing a heavy current through the area of the joint. Butt welding may be applied for welding pipes, tubing, rods, etc.

Fig. 32. Electric Arc Welding:

1 - carbon electrode; 2 - additive;3 - plate; 4 - weld

Electric arc welding is a process in which surfaces to be joined are fused together by the heat of an electric arc. The electric arc was invented in 1802 by the famous Russian scientist V. V. Petrov, who demonstrated the possibility of utilizing its heat for fusing metals. Fig. 32 shows the process of electric arc welding. By bringing the work and the electrode together as conductors, an electric circuit is

established. When the conductors are separated, an electric arc is created in which the electrical energy is converted into heat, its temperature being as high as 7000°F3. An additive is placed into the flame of the electrical arc. An additive is a metal which is externally applied to the place of welding and melted to form a weld together with the material of the work. The electric arc melts both the edges of the parts to be melted and the additive used. The electrode having been removed from the place of welding, the molten metal cools, solidifies and forms a weld, joining the parts of the work.

In autogenous (gas) welding the source of heat is the gas flame obtained from a gas which is often acetylene. Acetylene mixed with oxygen in a torch when ignited gives a steady flame. The welding torch consists essentially of a gas mixing chamber and is designed in two types: the low-pressure injector type and the equal-pressure type. In the injector-type torch the acetylene is delivered at very low pressure and the oxygen enters the torch at high pressure and velocity expanding in the mixing chamber. Then the acetylene is drawn by suction created in the mixing chamber in a constant ratio to the oxygen. Autogenous welding is carried out in different ways and methods. According to the movement of the torch, welding may be divided into rightward welding and leftward welding. In rightward welding the torch moves ahead of the additive, and in leftward welding the additive moves in front of the torch. In practice rightward welding is mostly used. Gas welding may be used for cutting metals and repairing agricultural machines and implements.