of the flange and to face the hub f. If the entire surface r is to be faced, it is necessary to use the face-plate jaws to hold it.

In Fig. 17 is shown one method of clamping a rocker-arm. A counterweight a is attached to the opposite side of the face plate and moved in or out until it balances the plate. The rocker-arm may also be held by passing a bolt through the slot b and the hole c, and placing a

washer and nut on the end of the bolt.

FIG. 19

(b)

Angle Plate.-The angle plate, Fig. 18, is so made that its two faces are at an angle of 90° with each other, and it is used when it is desired to finish two faces of a piece square with each other, as, for instance, the flanges of a pipe elbow.

A magnetic chuck, Fig. 19 (a), is useful for turning or grinding thin rings, washers, and also pieces of irregular shape. The

a

work is held against the face a of the chuck by magnetism. When the job is finished, both the face plate and the work (except hardened steel pieces) are demagnetized by opening the switch. The method of supplying the direct electric current to the coil in the chuck is shown in (b). Brushes in the holder c make contact with the two rings d and e that are insulated from each other and connected to opposite ends of the coil. Wooden Chucking.-Some contrivance can be arranged for almost any form of work by the exercise of a little ingenuity.

FIG. 20

For example, the outer surface of the ring a, Fig. 20, can be turned down by screwing it fast to a block of wood b, which is bolted to the face plate. The wood is first turned down to the proper size and faced up true on the front surface.

TURNING TOOLS

Forged Tools.-The most common forged tools are shown in Fig. 1; (a) is a round-nosed tool; (b) a broad-nosed finishing

(f)

(8)

(c)

FIG. 1

(h)

tool; (c) a cutting-off, or parting, tool; (d) a side tool; (e) a diamondpoint tool; (f) a boring tool, or inside threading tool, depending on the shape of the cutting edges; (g) a forming tool; and (h) a roughing tool. Round-nose, cutting off, diamond-point, and facing tools are made either right-hand or left-hand. Fig. 2 shows a tool formed by welding a piece a of high-speed steel

to a bar b of low-carbon steel. Fig. 3 shows threading tools, the shape of the cutting edge depending on the form of thread to be cut; (a) is an offset V-thread tool; (b) a right-hand square

thread tool; (c) an inserted-blade threading tool; (d) a special tool with ten teeth on its circumference, each one formed to cut deeper than the preceding one; (e) is a chaser or a tool used

to true up or finish the thread after it has been cut with another tool.

Tool Holders.-Tool holders are made of the same size as the shank of the ordinary forged tool, one holder is sufficient for a great variety of shapes of cutting points or blades. Figs. 4 and 5 are holders for square-tool steel, and Fig. 6 is a tool holder

with an adjustable cutter. A parting tool with inserted blade is shown in Fig. 7 and three forms of boring-tool holders in Fig. 8. In Fig. 9 is shown a knurling tool.

Form of Cutting Edge.-The angle of clearance is the angle DO H, Fig. 10. The angle of keenness is the angle E O H

between the cutting faces of the tool. The angle of clearance should be about 8° or 10° for iron or steel, and about 12° for soft metals as brass. The top front rake is the angle AO E and is the back slope of the top of the tool. For some classes of work, the tool is also given a top side rake which is represented by the angle MS V.

Effect of Kind of Metal on Shape of Tool.-In general, it may be stated that for soft material such as mild steel, the tool angles are smaller than for hard material such as chilled

CK

E

FIG. 10

cast iron; for materials that draw the tool in, as brass or copper, the angles may be made very blunt; in fact, negative rake is often given to them. When shavings of soft steel come off in large curls, and are very strong, the tool is properly ground and set. When the shavings come from the work broken in small pieces, incorrect setting or grinding is indicated.

Roughing and Finishing Cuts.-When a tool is set to take a long, heavy roughing cut, most of the cutting is done along the left-hand edge of the tool, the point doing a very small part of the work. The tool must, therefore, be given top side rake so as to give keenness along the cutting edge. When the tool is used for a finishing cut, the cut is very light, and most of the cutting

is done with the front edge of the tool. In such a case, plenty of top front rake should be given.

When the feed is coarse and the tool point broad, so that the rate of feed per revolution of the work is greater than the depth