All key-grooves which are to be formed along the entire lengths of their respective wheel-bosses and lever-bosses, may be easiest made with slotting-machines, because the lengths of the intended grooves will permit a free action of, and ample room for, the traverse of the cutting tools, both above and below the extreme ends of the grooves ; a space existing both at the upper and lower end of a groove from which the tool-edge may enter the metal and escape from it. A slotter is suitable for these key-ways, also because the length of a lever may extend to any distance from the place where the slotting-tool is cutting, without causing any inconvenience or requiring any el-chuck, as when the key-way is to be made with a planing-machine. But a slotter is not capable of grooving any portion of a long shaft or axle in the direction of the shaft's length, because it would be necessary to stand it with its length vertical, in which position it would occupy more room than can be obtained on a slotting-table. It may therefore be said that axles and other pieces of great length are preferably grooved with shaping, planing, or drilling; and short objects are preferably grooved with slotting-machines.

To cause a groove to be made in its intended place and position by means of slotting, it is necessary to adjust the wheel or lever on the table with regard to stated rules, as for adjusting objects on other machines. And for the convenience of effecting a rapid adjustment of an article previous to grooving, it must have been previously bored, turned, planed, or smoothly surfaced in some way to obtain uniform surfaces ; which surfaces constitute tangible and definitely formed curves and planes that can be quickly put into any position without trouble, and can be easily observed in any position, whether right or wrong; whereas a roughly formed surface requires considerable observation to discover which is the place where the mean curve or plane should be, or would be if produced; and which is that required for adjusting the rough surface. The surfaces of all articles to be slotted are those which must necessarily be placed in some stated position, or at some desired angle with the slotting-table; therefore the surface of the table is considered as the base or primary plane to which all objects are referred during adjustment. Concerning primary bases or planes, refer also to pages 208, 209, 210, and 214 ; also to the chapter on lathe-turning.

The proper placing of a lever on a slotting-table, to have a key-way cut, consists in laying it with its length at right-angles to the machine front, and with one of its smooth boss-faces parallel to the table. This face may be either in immediate contact with the table, or in contact with a packing-ring resting on the table, the upper and lower planes of the ring being parallel to each other and parallel to the table. A packing-ring of this sort is required to keep the lower boss-face of the lever parallel with the table, and at the same time to provide a space of sufficient height between the boss and the table to allow the slotting-tool to escape from the metal without touching the table's surface, the space into which the tool enters being the hole of the ring. Rings of this class should be of iron or steel, to avoid liability to bruises, and should be of various diameters to suit bosses of various sizes. A good substitute for such a ring consists of a couple of long parallel blocks, each of the same height, one of which is placed beneath the lever-boss at each side so that the tool shall be between. When two blocks of sufficient length cannot be obtained, four short ones may be used, which are placed at equal distances apart, and at any required radial distance from the centre of the hole, to suit the diameter of the object being fixed. Placing the article upon such parallel packing here referred to, immediately causes the length of the hole in the boss to be put parallel with the direction of the cutting tool's motion, and therefore at right-angles to the table-face, which will cause the length of the key-way when formed to be parallel with the length of the cylindrical hole in the boss, as required. The object is consequently put into one of the positions necessary, and without trouble. It is next adjusted to make the lever's length exactly parallel with the traverse of one of the slide-rest screws, which screw is the one that advances the table and object from the front of the machine towards the back, or from the back towards the front. If the lever were not thus adjusted, the depth of the key-way would not be parallel with the diameter of the hole; or, which amounts to the same thing, the width of the key-way would not be at right-angles to the length of the lever.

It is now requisite to place the object into its proper situation under the tool, because the tool cannot be shifted to place it exactly over the intended key-way. The table and object are therefore gradually moved to the desired spot by rotating the two traverse screws of the slide-rest.

It may be seen that the lever has to be fixed with regard to three positions while on the table: with its boss-faces parallel to the table ; with its length parallel with the direction of the traverse that advances the lever during cutting; and with the length of the key-way which is to be made, exactly under the slotting-tool. To render the movement of a heavy lever easy, while placing it at right-angles, poppets are used, the screw-points of which are in contact with the lever, while the poppets are tightly fixed to that part of the table convenient for the purpose. Poppets for slotting-tables are similar to those for planing-tables, (see page 239).

To facilitate the adjustment of the lever's length to parallelism with the traverse which effects the slotting, the right-angular lines on the table-face should be used, which are marked in the Figure 834, and are analogous to similar lines on shaping-tables and planing-tables, described in page 225.

To mark these gauge-lines upon a slotting-table, the traverse of the slide-rest should be employed, if the distance between the table and the main standard of the machine will permit, because the traverse will easily mark deep lines that can be plainly seen when required. The tool used for marking, is one of the slotting-tools of the machine, and is a straight tool having a thin end and a sharp vee-point. The tool is tightly fixed in the tool-clamps and gradually adjusted to the table's surface by rotating the lifting or lowering screw of the main-slide, which screw is shown by L S in Fig. 834. It is also now necessary to fix the table with respect to its rotary movement, which is done with a couple of screw-bolts and nuts, and when fixed, an el-square is placed with its blade to the table's edge and its pedestal upon the slide beneath, for the purpose of scribing a line upon the table's edge at the edge of the blade, and scribing another line upon the slide beneath at the edge of the pedestal. Such marks will be useful when it is required to again place the table into the same relative position. When the table is thus prevented from rotating, it is slowly advanced to the tool-point, the point being adjusted to enter the metal a proper distance for making a deep mark. The advancement of the table is next effected by rotating the traverse screw with a handle or with a longer lever, which belongs to the machine, if a large one. If there is room to advance the table and make a line entirely across it, the traverse is continued accordingly; and when the tool is released from the table's edge, the table is shifted into a situation for receiving another mark parallel with the first one. This shifting of the table is effected by working the other traverse screw, which is the one not used to mark the line, but which moves the table in a direction at right-angles to its motion while marking. When the table is thus moved three or four inches, according to the distance desired between the lines, it is again advanced to the tool-point, and another line marked by rotating the traverse screw before used; but this time, it is rotated in the opposite direction, which avoids the necessity of working back the table and commencing the second line at the same side as the first one.

By means of several shiftings of this sort and advancements of the table in contact with the tool-point, the required number of parallel lines are marked; consequently, the next step is to mark another lot of lines which shall be also parallel with each other, but at right-angles to the lot first marked. The second marking is conducted by the same means as that for the first, with the difference of advancing the table while in contact with the tool-point, by means of the traverse screw at right angles to the one used for marking the first lot.

When it happens that there is not room enough to move the table and make the lines entirely across, they may be partly marked with a straight tool, and afterwards completed with a cranked tool; or they may be completed with a straight-edge and scriber.