In general, the bosses of a lever are both bored and their outsides turned, while the lever remains on a lathe-chuck. This avoids the necessity of fitting and handling an arbor with the lever thereon, and is also an easier mode of turning the outsides of all large bosses, because the slide-rest can be advanced to the centre, and thus be close to the portion being turned. In this arrangement, the cutting tool will occupy nearly the same place that would be occupied by the arbor, if an arbor were to be used for the turning.

The first treatment of a large lever after forging, should consist in planing one of its broad sides. This side is that which is flat, or nearly so, being the side in which the two boss-faces are nearly or quite level with the arm. This is termed the connecting-rod side, or piston-rod side, and is the bottom surface of the lever shown by Fig. 1042. While this is being planed, the lever is held with poppets of proper height, which are caused to bite the bosses and also the narrow sides of the arm. If a great quantity of metal is to be cut off the boss-faces and the broad sides, and but little from the other surfaces, which is the case if the lever is properly forged, the object is adjusted on the machine until the lengths of the bosses and narrow sides of the arm are square to the table, without regard to whether the boss-faces are parallel with the table. To put the article into the proper position, wedges and thin packing-pieces are driven in between the bottom side and the planing-table, an el-square resting on the table and applied during adjustment.

The planing of the lever consists in making the entire broad side plane ; no boss-ends being considered because the boss-ends for this side will be very short, if any at all are to be formed. Large levers are never forged with such short projections, but having one broad side of each lever flat. Consequently, if the short ends are to be produced, they are entirely formed by lathe-turning. This broad side is therefore the one which is considered as a primary plane, with regard to which the adjustments and lining operations are conducted.

Nearly all levers are forged without any hole. It is therefore requisite to first roughly remove the comparative large amount of superfluous metal in the bosses, previous to finally boring each boss-hole accurately to the diameter required. The boring of a large lever commences with a powerful vertical boring-machine or driller, and concludes with an accurate boring on a lathe-chuck, because a lathe is not so well adapted as a driller to quickly remove a large amount of metal from the hole, and a drilling-machine is not so efficient as a lathe for a final correct shaping. But there are means whereby a vertical driller can be used to both commence and finish a large hole correctly; these processes require special boring and cutting apparatus, which will be described.

A lever must be bored so that the centre-lengths of both holes in the bosses are parallel with each other, and also at the precise distance apart which is necessary. This distance is the length of the crank's throw, and it is marked previous to boring either boss. The marking is done by means of a primary centre-line which is scribed across those two rough boss-faces that are opposite to those which are planed.

The methods by which such centre lines should be scribed, are shown by Figs. 1040 and 1041. When it happens that the arm of the lever is nearest to the specified width, four centre dots are put into the arm at about a sixteenth or an eighth of an inch from the edges in the places indicated in Fig. 1040. These dots are shown by the letter C, and constitute centres from which four arcs are scribed, which are seen on the boss-faces. The exact situations of these arcs are of no importance, but it will be seen that their points of intersection indicate the place for the required primary line. A straight-edge is therefore put to these points and the line scribed. It is not necessary to mark the line along the entire length of the arm unless it happens to be nearly level with the boss-faces; in which case the straight-edge is slightly bent to the arm while marking. It is also necessary to bend it while scribing the bosses if one is longer than the other.

When the bosses of the lever have but little metal to be turned off to attain the specified diameters, the centre line should be found by the lining given in Fig. 1041. In this case the centre-dots from which the four arcs are scribed are put near the edges of the bosses, as indicated by the letters C, from which points the arcs are caused to intersect and show the straight centre line as seen in the Figure. It may be here mentioned that the centre lines which are marked by these means, are also centrally located with regard to the opposite broad sides of their respective levers, because these were planed while the bosses and narrow sides of the arms were situated square to the planing-table, as directed. Consequently, as soon as a straight centre line is marked, the length between the centres of the two required holes can be shown, and dots are put at these places from which to scribe circles showing the diameters and situations for the holes.

It is to be here noted that the length of the lever's throw is the length of a straight line which is parallel to the planed level broad side of the lever; but if the bosses are of different lengths at the time of scribing the length of the throw, the straight line represented by the distance between the points of the compasses, or points of radius-gauge, with which the scribing is performed, will not be parallel to the plane side of the lever, and some error may thus occur in the marking. To obviate this, the scribing may be done with a wire gauge or bar-gauge having a pointed arm at each end bent square to the length of the gauge. One of these arms is longer than the other, and is just as much longer as one of the lever's bosses is longer than the other. With this gauge the length can therefore be properly marked after a centre-dot is put into one boss, the point of the longest arm of the gauge being put over the shortest boss.

While applying a gauge with arms of unequal length to a measure for adjusting it to a specified distance, the length of the gauge must be kept parallel with the length of the rule or measure; therefore a broad rule of sufficient width is necessary because the point belonging to the short arm of the gauge will be further from one edge of the rule than the point of the long arm. The use of bar-gauges for lining levers can be avoided by scribing the lengths of throws upon the flat plane sides, in which cases it is necessary to plane both sides of each lever to allow it to be properly adjusted for boring. But it may be said that planing is only requisite for levers which are very irregular when forged; if the boss-faces are smooth and square to the lengths of the bosses and sides of the arms, the lengths of the throws should be marked upon the flat sides without any preliminary planing whatever.

Where convenient lifting apparatus is accessible, any lever, small or large, can be easily and quickly lined on a lining-table; the length of throw being marked upon both sides of the lever with a tall scriber-block while the lever is held up lengthways on the table.