The boss is now marked with a set of lines which resemble those marked with a scriber-block on a lining-table; and lines are also scribed equidistant from the centre ones, to show the thickness of the key-slot required, which lines are seen in Fig. 908. In addition to these, lines can be marked to show the place of the key-slot in the hole of the boss; for which purpose the bisector is put with its blade in the hole, and the pedestal near the hole's edge, as represented in Fig. 909; which will allow lines to be scribed in the hole opposite each other, and thus indicate the place of the key-slot in the hole, in addition to indicating it outside, this marking being especially advisable when a large boss is in progress. One of the author's bisectors is described in page 113. When it may be desirable to mark the key-way in the hole of a lever-boss on a lining-table as in Fig. 904, it is only necessary to use a scriber-block having a scriber of sufficient length to extend to the proper place in the hole; so that after the scriber is adjusted and the outer surface of the boss marked, the scriber can be put into the hole, and the necessary lines marked. These must necessarily be at the same height as the others, because the height of the scriber is the same for all.

There is also a mode of scribing the outer surface of the boss, and also the hole, without using a bisector. This plan involves a little extra moving and lining of the lever, because it is necessary to mark centre lines across both the faces of the boss, instead of only one. Therefore, the same lines shown on one boss-face are also scribed upon the opposite face; and two enders are used, one at each mouth of the hole, to denote the two centres required. When the two centre lines are shown, four extremities are shown, two for each line, and of these four two are shown in Fig. 907, by E and E, one at each face. The straight line between these two, which is that required to show the centre of one mouth for the key-way, is easily marked by merely placing a straight-edge and scribing. The centre of the other mouth or entrance is also shown by a similar scribing.

The lining of a crosshead to show its intended key-way, is similar to that for a lever, and can be executed without removal to a lining-table. The primary lines with which the lining commences, are the straight lines along the middles of the narrow sides of the arms ; these are intersected by two circles, one on each boss-face, each circle being concentric with the face, because of being scribed from the centre-dot existing on the ender at the hole's mouth. Such lines are therefore analogous to those on a lever-boss. At the two points shown by the letter C in Fig. 912, which points are plainly shown in the larger sketch, Fig. 911, where the circle intersects the straight line on the face, a compass-point is put, and with the other point short arcs are marked which intersect on the boss-face near its edge. The distance between these two points where the arcs intersect, is a straight line which is right angular to the length of the crosshead, and also passes through the centre-dot at the end of the hole. A straight-edge is therefore put to the two points and the line scribed across the face. One end of the boss being thus treated, the opposite end or face is next treated in a similar manner, to show another centre line right-angular to the crosshead's length. These two lines are two boundaries of a plane that distinguishes the boss into halves; and it is now needful to scribe the other two boundaries of this plane, which are two straight lines along the length of the boss, one on each side of it, and so situate that the extremities shall exactly coincide with the extremities of the straight lines across the boss-faces. One of these two lines is denoted by E and E in Fig. 913, and is easily marked by merely placing a straight-edge, as for marking a lever-boss.

As soon as the centre lines along the outside of the boss are scribed, they can be used as centres from which the thickness of the key-way is marked; and its width also marked. By this lining the two entrances for the key-way are correctly delineated opposite each other; or in other words, are correctly shown at each extremity of a diameter of the boss-hole. The lines for one mouth of the key-slot, are indicated in Fig. 914.

In some cases it is requisite to form key-ways at some other angle than a right-angle to the length of the lever or crosshead, for which no special lining is required to mark a line across one boss-face; it being only necessary to place a straight-edge upon the face at the desired angle, and mark the line. A centre line of this character is seen on the boss-face in Fig. 924. To mark another line upon the other face, which line shall be at the same angle to the crosshead as the first one, it is only necessary to provide a circular line on each face, both of one diameter, and measure from the intersection of the line referred to with the circle, to the intersection of the centre length of the crosshead. This distance is ascertained with a compasses, and marked upon the opposite face of the boss, as required, by applying the compasses with one point at the intersection of the crosshead's centre line, and the other point reaching to the circular line at a point which shows the place for the desired straight line, which is therefore marked by placing a straight-edge to the point and to the centre of the hole's entrance. When the two analogous straight lines across the two faces are thus shown, a straight-edge is put to the side of the boss and to the two lines, and a line is scribed to show the centre of the desired key-slot, which line is exactly analogous to the one seen extending from the top to the bottom of the boss in Fig. 913, although it is at a different angle to the length of the crosshead.

After a lever or crosshead is lined by some of the means just given, to show the key-way, it is adjusted either on an ordinary driller or on a slot driller for cutting out the metal, and this adjustment is conducted with regard to the same gauge-lines across the centre of the boss-face which were used to mark the key-way; therefore if the object is bolted to an el-chuck on a drilling-table, the end of the lever or crosshead is raised or lowered until the line across the face is seen to be vertical, which is square to the table, and parallel with the downward vertical motion that executes the drilling. By referring to Fig. 925, a lever may be seen which is in position for drilling, supposing that the key-slot is to be square to the lever's length, which is the usual arrangement. Consequently, the centre length of the lever marked along the broad side is parallel with the drilling-table, and the line across the face showing the centre of the key-way's mouth is at right-angles, as denoted by the el-square blade seen in contact. Fig. 926 represents a crosshead, the key-way of which is to be in this same right-angular position; for which reason the adjustment is effected by the same means. The crosshead seen in Fig. 924 is required to have its key-way inclined to the centre length, and is therefore bolted against an el-chuck of suitable height and supported on packing-blocks; the line for the key-way being placed vertical, as for the others, but the crosshead is inclined at the proper angle.

When one side of the boss has been drilled, it is put upside-down, if a large one, and again fixed to drill the other side. After drilling, the key-way can be completed with a slotting-tool while on a slotting-table, because, by slotting, the desired uniform shape for the key-way can be accurately produced along its entire length.