The most rapid and effectual mode of shaping outsides of lever-bosses in large numbers is slotting; the object to be shaped being fixed on a slotting-table and rotated by means of the worm-wheel and pinion of the machine.

Any boss, small or large, to be thus shaped, requires fixing with the centre of the hole in the boss in a straight line with the axis of the machine-table's rotation; or rather, with the centre length of the hole and the table's axis both in the same straight line. This situation is occupied by the small lever on the table of Fig. 862, and is necessary because the outside of the boss when shaped, is to be concentric with the hole, which condition is termed, true with the hole, and results from the cutting tool acting in contact with the boss while it is gradually rotated with the table.

Each lever-boss, previous to slotting, is bored to make the hole of the required finished diameter, and its two faces are smoothly turned to make them parallel with each other and right-angular to the length of the hole. One of these faces is selected to be placed into contact with a parallel ring, or with a few parallel packing-blocks, that the length of the hole may be accurately placed at right-angles to the table, and that a space may be provided beneath the boss for the escape of the tool from the metal, which space resembles that required while slotting a key-way. For shaping the outside of a boss, it is necessary for the outer edges of the parallel ring, or other packing that may be used, to be entirely within the extreme finished diameter of the boss, that the tool may be prevented from touching any portion of the packing at the time of cutting; whereas, while slotting a key-way, the outer extent of the ring is not important, unless it is large enough to obstruct the fixing of the holdfast bolts. The thickness or height above the table of this packing, is about the same, whether for key-way cutting or for shaping bosses, and is sufficient to allow ample room for the tool-edge to disengage from the metal at the conclusion of each cut and not incur any risk of causing the edge to touch the table and do mischief, the height being usually from half an inch to an inch.

When the boss is thus supported parallel with the table, it is held in position with a couple of holdfast plates and bolts, which are placed opposite each other and at the two inner edges of the hole in the boss. If two bolts cannot be placed, through the smallness of the hole, or through a deficiency of slots in the table, one bolt is employed and is put at the middle; consequently, a plate having a hole in the middle is employed to grip the boss-face. Supposing that the article to be shaped is an ordinary lever with two bosses, the other end of the lever, which is not near the centre of the table, now requires supporting, especially if it is a large one, to prevent its length and consequent leverage exerting an injurious strain upon the screw bolts or bolt holding the boss. To avoid this, the end of the lever is allowed to rest on one or more packing blocks of the proper height, which height is just sufficient to sustain the weight of the lever-arm without affecting the parallelism with the table of the face belonging to the boss to be shaped. When it happens that the lever is not too long for both its bosses to rest on the table, the packing consists of parallel blocks, and they are placed between the surface of the table and the under surface of the outer boss; but if the lever is long enough to cause the outer boss to extend beyond the table's edge, the packing consists of blocks which are rather taper, and they are put beneath some portion of the arm or intermediate portion.

A large boss of ten, twelve, or fourteen inches in diameter, can be easily fastened to the table with bolts situated in the hole, and such bolts will not hinder the final adjustment of the boss to the exact situation required. A few poppets also can be placed along the lever-arm, and holdfast plates fixed across the top of the arm. All these fastenings may be attached before the object is precisely adjusted ready for work; they are therefore not tightened until adjustment is completed. But a small lever that may have a boss only about two or three inches in diameter, when to be shaped by slotting, must be fixed, either without any bolt in the hole of the boss at the middle of the table, or with a bolt which is put into the hole after the boss is finally adjusted. When bolts are put into such a small hole they sometimes prevent the observer seeing the bottom of the hole, and therefore adjustment is hindered. It is, consequently, necessary to first hold such a boss with a couple of plates and bolts at the outer edges of the boss, instead of at the inner edges; and while these are attached, the bottom of the hole can be adjusted as required, because the hole is empty. After adjustment, the necessary bolt or bolts can be put into the hole, and those that were put to the outer edges are removed, not being now needed, and which must he removed to allow the boss to be shaped. Small lever-bosses are rapidly and accurately adjusted by means of arbor-chucks, which are described in the next section.

Adjusting the boss to place it exactly in line with the table's rotation, or in line with the axis, is done with the poppets which gradually shift the object to the proper place. In order to ascertain the amount of shifting that may be needed to effect the adjustment, it is necessary to use the circular gauge-lines which are marked a short distance apart on the table-face. About twenty or thirty of these exist on the table, all being concentric with each other and with the table's axis of rotation. Therefore, any one of these circular lines which is conveniently situated for the diameter of the hole may be selected, and considered as a gauge-ring in which the truly formed hole of the boss shall be centrally located when adjusted. If the hole is large enough to admit an el-square, one of the gauge-lines which is of less diameter than that of the hole, may be selected, and the square put into the hole with its pedestal on the line on the table, and, consequently, with the blade extending upwards to the top of the hole. The bottom corner of the pedestal is put exactly upon some point in the circular line, at the time the situation of the boss is to be ascertained, and the distance between the edge of the blade and the side of the hole is then measured with an inside calliper. The square is next shifted to the opposite side of the hole, and stood upon the same gauge-line on which it stood before, but being now at the opposite side of the centre. The distance between the blade's edge and the side of the hole is now measured as before, and if found to be the same as when the square stood at the opposite side, the boss is in its proper place ; if not, it is shifted, and again tried with the square in the hole as before. Two or three couples of opposite points in the gauge-circle should be selected on which to stand the square, in order to avoid being misled by using only two points, although two are sufficient, if the observation and measurements are accurately conducted. It may be mentioned that this mode of adjustment is most effectual with bosses having large holes, which permit an easy observation therein. The method is applicable to the fixing of bosses having either parallel holes or taper ones; but for a taper hole, the operator must exercise due care to measure the distance between the blade and the upper extreme edge of the hole, each time he applies the callipers, and not to place the callipers to any portion of the hole below the edge.

The boss can be adjusted also by means of a scriber-block. For this purpose a wood or iron ender is fitted to the boss-hole at that end which is uppermost while the boss is on the table. The ender is used to mark the centre of the hole's mouth, which is found with a compasses. From this centre, circular lines are scribed upon the boss-face; of which lines one denotes the diameter to which the boss is to be finished. Either this line or one of the others on the face, which may be more convenient, is selected for a gauge-line by which the boss is to be adjusted. The desired result is obtained by placing the line or lines exactly concentric with the axis, as intended. To do this the scriber-block is now stood upon the table with the bottom edge exactly coinciding with some point in one of its circular lines; and while it thus stands, the scriber-point is adjusted to a point in one of the gauge-circles on the boss-face. The scriber-point used for this purpose, is the one at the bent end of the scriber, which will allow the observer to see clearly whether or not the line on the boss-face is exactly beneath the point; and, consequently, will enable him to discover the precise amount of shifting of the boss which is required to adjust it. After the scriber-block has been stood at one side of the boss on one of the table's lines, the block is removed to the opposite side of the boss, and stood upon the same circular line, but now upon a point which is opposite to the point on which it stood before. By now observing the scriber-point and the gauge-line on the boss beneath, the relative positions of the two are seen, and the boss is gradually shifted until its gauge-lines show it to be in the proper place.

A boss may be adjusted concentric with the table, also by observing the edge or mouth of the hole. For this adjustment the edge of the hole must be sharp, instead of curved, which is an ordinary shape of a large number. If sharp, the scriber-point of the scriber-block can be put to the edge and observed, instead of placing the point to a circular gauge-line scribed on the boss-face, the operation being similar to the adjustment by placing the scriber-point to the line on the face, as given in the preceding paragraph.