The shaping of a half-round gap can be easily managed on a slotting-machine having a worm-wheel motion. On a slotting-table a brass or other object can be completely rotated if necessary, by reason of the table having a complete circular worm-wheel, instead of only a sector. To adjust a half-round brass on a slotting-table, it is placed upon a parallel ring or blocks near the middle of the. table, with the length of the desired gap vertical, because the motion of a slotting-tool is vertical. The brass is situated between the machine-front and the tool; and the adjustment must be conducted without reference to the half-round gauge-line which is near the table, this line being quite hidden from the operator. The bottom surface on which this line is scribed, must be square to the length of the gap, and also square to the flat sides of the brass termed faces, which are those that adjoin the mouth of the gap, and are nearest to the slotting-tool. If these faces are right-angular to the bottom surface, they must necessarily be vertical,, while the brass remains on the parallel packing; and because these vertical faces are parallel with the gap to be made, the brass is known to be in position by the blade of an el-square, which is put to the faces while the square's pedestal rests in contact with the table.

When the brass is placed square to the table, it is ready for adjustment by the half-round line on the top surface. This is to be put concentric with the table's axis of motion, because this motion is that which will rotate the brass during the cutting. A tool-scriber may therefore be fixed in the tool-clamps, and gently lowered until the point is very near the gauge-line ; the table, and therefore the brass, is now rotated, and the point observed, which will show exactly how much shifting of the brass is necessary to place the line concentric with the table. The small movement for this adjustment is effected with the poppets which are near the brass and fastened to the table, and also with the traverse screws; and after the brass is correctly situated and fastened with plates across the top, it is ready for the shaping by rotating the worm-wheel.

The tools employed for slotting a half-round gap are the slotted ones shown by Figs. 786 and 788 ; and the solid ones shown by Figs. 793 and 794. While a tool is being fixed in the tool-clamps, the cutting edge is adjusted to the exact height intended, in order to prevent it extending too far below the lower edge of the brass during the downward travel, and thus prevent it coming into contact with the table.

Whenever it happens that several pairs of large brasses require to be shaped with a slotter, two should be fixed at one time on the table, and slotted at one operation. By this plan, each two brasses which constitute a pair or couple, are fixed together, so that both brasses can be shaped at one rotation of the table.

It may be also stated that because the cutting-tools of slotting-machines cannot be easily adjusted every time to the same relative position with the gauge-lines on the object beneath, it is necessary to shift the table and object thereon a short distance, when it is seen that the metal is not being equally cut off concentric with the gauge-line or lines.

Shaping the concave junctions of a crosshead, lover, or bar, by means of a circular motion, is, in most cases, easier performed with a to-and-fro sliaper than with a slotter, unless the lever or bar is several feet in length. An object situate on a shaping-table always presents the surface which is to be reduced in a horizontal position, which allows the operator an easy and full view of all operations while he stands in an ordinary vertical position. This is of considerable importance ; but such a view of an object on a slotting-table cannot always be obtained, especially while it is placed for shaping a concave junction, the surface of which is hidden from the operator, unless he is situate between the tool and the F-standard.

For the production of each surface belonging to a concave junction of a bar, crosshead, or other article, the article requires a distinct adjusting process, that the gauge-line showing the desired curve may be adjusted concentric with the table's curved motion. Therefore, a three-boss lever would require eight adjustments, in addition to the several fixings for shaping the cylindrical parts of the bosses and the eight flat surfaces of the two straight arms. And a crosshead having one boss in the middle would also require eight adjustments for similar purposes. The tedium connected with such a number of operations should, therefore, be placed against any advantage that may be considered to result from adopting such a course. Perhaps the principal consideration is the great ease and order with which the metal can be removed and the concave surface produced after the object is once properly adjusted.

As soon as the gauge-line is properly placed and the object fastened to the table, the shaping or paring of the junction proceeds by the action of the rotating apparatus, and by using any ordinary vee-point tool, whether the object is on a shaping-table or on a slotting-table. No broad-point tool is required from the commencement to the end, nor any springy tool. The entire paring can be executed by removing slices with the point-tools, because the travel of the object in a curved path while being reduced is quite as easy as the travel of an object in a straight path while being reduced, the only tedium belonging to the process being the adjustment for each curved surface which has to be formed. By using a sharp vee-tool, the point of which is slightly convex, and applying soapy water during the removal of" the last slice, the surface is entirely finished, and no filing is afterwards needed, except a small quantity at the places where the concave junction merges into the convex boss, and merges into the straight part of the arm. But a junction that is machined with broad-point tools and springy tools, for the purpose of avoiding the adjustment for the rotary movement, requires the entire curved surface to be afterwards filed, and in some cases also chipped, unless the lever or crosshead in process is very small; if so, its junctions can be smoothly finished with a springy tool having a broad convex edge. It may, therefore, be easily perceived that large junctions in general should be finished with vee-point tools and the circular traverse of the table ; and that small junctions in general should be finished with the straight to-and-fro movement of a shaper or slotter and the use of springy tools.

The shaping of a half-round gap belonging to a U-end connecting-rod is easily executed by boring or by turning ; but when it is imperative to produce such a gap by the curved motion of a shaper or slotter, the rod is fixed with its length either vertical or horizontal, according to the machine selected. The processes for adjusting are very similar to those described for joint-gaps having plane sides, in pages 283, 284, 285, and 286.