When a large number of bosses having holes of the same diameter are to be shaped, they can be quickly and accurately placed to their proper situations on the slotting-table by using an arbor-chuck. This implement consists of a cylindrical piece of iron or steel which is provided with a broad base or flange. The flange is exactly at right-angles to the cylindrical part or stem, and is large enough to contain holes for fixing-bolts, with which the chuck is bolted to the slotting-table. The diameter of the stem or pivot-portion, just suits the holes of the bosses to be shaped, and allows any boss to be easily put on, and at the same time to be tight enough to prevent the boss moving sideways while situated on the stem. If the stem is cylindrical along its entire length, it can only fit bosses with holes of one diameter; therefore, to make one arbor suit holes of different diameters it should be turned to two or three diameters along its length, so that one portion will fit holes of one size, and the other portions will fit holes of other sizes. The smallest diameter of the stem is at its end or point, at its largest diameter at the bottom; consequently, it may be termed, stepped. The entire chuck is truly lathe-turned, to cause any portion of its stem to be concentric with any other portion, and also to make the length of the stem exactly right-angular to the flange; if in this condition, the length of the stem is immediately placed right-angular to the slotting-table as required, by placing the face of the flange into contact with the table-face. The outer surface of the flange termed its edge or rim must be turned to make it concentric with the arbor or pivot, because by the rim of the flange the chuck is sometimes adjusted. By turning, the two broad sides of the flange are also made parallel with each other; and of these two sides, the outer one is that which is bolted in contact with the table when in use, the inner broad side being often required to be in contact with one face of a boss or other object to be shaped.

When the chuck is to be used, it is bolted to the table so that its stem may extend upwards, in which position it is ready for the boss to be put thereon. The outer edge or rim of the flange may now be used, for adjustment, which consists in placing it exactly concentric with the table's rotation, the stem being, of course, adjusted by the same act, because it is concentric with the rim. To gradually shift the chuck, during adjustment, a tin hammer is used, and a few blows are given previous to tightening the fixing bolts, the proper place for the chuck being known by its being centrally located in one of the gauge circles on the table. By reason of the implement being thus fixed to the table, both the table and chuck must rotate together, and also the boss thereon.

The chuck can be adjusted also by means of a shallow recess in the table, into which the edge of the flange is put, which immediately places the chuck concentric with the table, because the recess was formed by lathe turning and is concentric with the axis of rotation.

Many slotting-tables are provided with holes at their middles, such holes being required to provide spaces for the slotting tools and for containing stems of various objects. If the mouth of a hole of this class is sharp, and true with the table, the flange of the arbor-chuck may be furnished with a short projection, the diameter of which is exactly the same as that of the hole in the table; and by this projecting part being put into the hole the chuck is adjusted without further treatment. This means should be adopted for all work that requires the chuck to be frequently and quickly adjusted to the proper place.

The chuck is held on the table with a couple of screws which fit holes in the flange, the holes having broad mouths for containing the entire heads of the screws when tightened. This arrangement allows the upper surface of the flange to remain quite free from any projection after the chuck is fastened; so that a boss-face or other surface can be put into close contact with the flange, or into contact with a parallel ring on the flange, whenever it may be requisite.

An arbor-chuck which has a stem of two or three different diameters must cause all bosses placed thereon to remain several inches above the flange, and therefore also above the slotting-table, except those that happen to fit the lowest portion of the stem, which is its junction with the flange. If the hole of a boss fits this portion, the boss-face can lie in close contact with the

2n2 flange while fixed, and no additional support beneath is required. But when a boss is held up at a distance from the flange, by reason of the hole fitting some comparative small portion of the stem's upper end, the boss is deprived of support beneath, and it is therefore necessary to pack up the boss. For this packing up either parallel blocks or parallel rings are used, a proper number being put between the boss-face and the flange to occupy the space.

When a great number of small lever-bosses having holes of the same diameter require shaping, an arbor-chuck with a stem long enough for three or four bosses should be provided, the stem being parallel along its entire length. On such a stem several bosses may be situated one above another, with their faces in contact with each other, in which positions all may be shaped at one traverse of the cutting tool. Lever-bosses thus arranged are quickly shaped, and also made uniform with each other without much lining or measurement.

A boss which is to be shaped while on an arbor can have but few fastening plates near the boss; consequently, the holdfast plates are put along the arm, together with a couple at the curved junctions near the boss which is on the arbor. This mode of fastening is suited to large objects; small levers can be held by means of a centre bolt in the extremity or point of the arbor. This bolt fits a screwed hole at the centre of the extremity, the length of the hole and the length of the arbor being in the same straight line. The head of this bolt bears upon a circular plate or washer, and the washer bears upon the boss-face ; so that by tightening the bolt the boss is fixed. To prevent the rim of the washer touching the tool while cutting, its diameter is rather less than the finished diameter of the boss. Several washers may be used, if necessary, one above another, and are required when the upper end of the arbor extends beyond the upper face of the boss.

While a lever remains on the slotting-table fixed to an arbor, or to any other packing or rings for holding it to be slotted, the length of the lever is across the operator while he faces the machine-front, the lever extending either to the right hand or to the left. During the rotation of the piece while shaping is progressing, its length usually travels towards the machine-front, and, consequently, towards the operator, and not towards the main standard of the machine. If it travelled towards the standard, it would be necessary that the boss being shaped should be situated between the cutting tool and the standard ; and such an arrangement would suit only those machines the cutting tools of which are not released from the metal during their upward motions. In a machine whose tool is released, the releasing movement causes the tool to retreat backwards from the machine-front towards the main standard ; therefore, on such a machine, the boss to be shaped must be situated between the cutting tool and the machine-front. If thus situated, ample room exists for the tool to retreat from the metal, which could not exist if the boss were at the back of the tool and obstructed its backward retreating motion.

When a boss is properly fixed on the machine with regard to the proper relative positions, it is ready for placing into the desired situation near the cutting tool. The movement for this purpose is easily effected by rotating the traverse screws, by which means the boss is gradually moved until the centre of the tool edge is found to be in line with the centre diameter or minor axis of the hole in the boss. This relative situation is analogous to that of a lever-boss which is adjusted ready for shaping with a to-and-fro shaper, and is mentioned in page 271.

The cutting tools used to remove the metal from a boss during slotting are those shown by Figs. 787, 788, 793, and 794, and are described in pages 257 and 258. While one of these is in the tool-clamps, the table, and, consequently, the boss attached, is advanced to the tool by one of the transverse screws. This screw is the one which advances the table towards the machine's main standard, and by this screw the thickness of metal to be cut off during any one rotation of the boss is determined, the other traverse screw at right-angles not being used after the boss is once adjusted, but remaining fixed. The lever is therefore advanced to remove a slice from the boss of the intended thickness, the thickness of slice depending on the power of the machine or the quantity to be cut off. One slice is removed at each rotation of the boss, until it is reduced to the intended diameter ; and Avhen polishing is necessary it is done with sharp tools and soapy water, as described for other work.