It is now requisite to mention the means for advancing the cutting-tool across the work and table, to effect the planing of the work while it moves to and fro. The direction in which the tool moves, and the various modes of moving it, are independent of the principles just given; whether it cuts while moving towards the operator standing at the front edge of the table, or cuts while travelling from him, or cuts while moving in both directions, is of importance only with regard to facilitating the work. In the earlier machines the workman moved the tool by rotating the traverse screw with a handle similar to that shown by H in the Figure ; and the tool was made to cut while moving either way, according to the direction in which the handle moved. To avoid the tedium of this hand-traverse, a variety of apparatus are now used which are worked by the machines themselves; so that the same power which moves the table to and fro, is made to move the tool across the work. Such apparatus is termed feed gear or traverse gear, and the greater number of all such gear are actuated by feed-rods. A rod of this class is denoted by its name in the Figure, and its use is to impart a rotary motion to the traverse screw by means of levers, rods, and pawls, that are connected to the feed-rod and teeth-wheels on the end of the traverse screw. For this purpose, the rod is made to move upwards and downwards once during every travel of the table to and fro; and this up-and-down motion is obtained by a spindle and levers attached to the lower end of the rod, these levers being moved a short distance at every travel of the table by receiving a gentle knock from a stud or pin projecting from the table and situated just below its front edge. Two of these studs or pins are provided, and are named stops. These are fastened to the table either by a dove-tail ridge extending along the table's entire length, or by a dove-tail groove, the bases or bottoms of the stops being made to suit, so that they will fit any place along the groove. Each stop has a fixing screw, which is tightened and loosened with a spanner by the workman. Stops effect two results, one of which is knocking the lever and shifting the feed-rod, and the other result is shifting the band or bands on the machine-pulleys to reverse the direction of the table's motion. For this reason, the stops are at various distances from each other, according to the distance that the table is required to move in one travel. If only a very small surface is to be planed, the planer fixes the stops very near to each other, that the motion of the table may be stopped and reversed immediately the tool becomes free of the work, to avoid loss of time; but if a surface whose length is nearly that of the table, is to be planed, he fixes each stop at one end of the table, and the desired length of the table's travel is thus obtained.

The necessity for a gradual traverse of the tool over the surface being planed, arises from the fact that there is no machine capable of planing a piece of engine-work, so that more than half an inch, or an inch, of the tool's cutting edge shall cut at one time, the usual length of a tool's cutting edge in actual contact while cutting, being only about an eighth, or a quarter of an inch. If a machine could be made to cut off a slice of four feet in width and a quarter of an inch in thickness, at one effort or travel of the table, the cutting edge of the tool must be quite straight and four feet in length, the entire cutting edge must also be in contact with the metal during the whole time of cutting, to produce a plane by such means, and no travel or movement of the tool in any direction, would be necessary. But because this cannot yet be done, the entire planing of the surface is gradually performed by cutting off only a portion of the slice at each travel of the table, by using a pointed tool; consequently, the traverse by feed gear or other means, is indispensable. By these considerations it may be perceived that the precise amount of metal to be cut off, the time in which it is done, and other circumstances attending it, require distinct terms. The entire quantity of metal to be cut off any one side or surface of an object, in order to reach the hidden plane, is the krap; and the quantity which is cut off during only one traverse of the tool across the machine, or during one planing of the side, is a slice; therefore, if three-quarters of an inch is to be cut off, three slices, each a quarter thick, will be the entire krap. During one travel of the table in either direction, only a narrow strip or ribbon of metal is cut off, and this is the only portion to be named a cut. If a machine will cut the metal while travelling in both directions, it is a double cut planing-machine. A cut may be termed an element or portion of a slice, and a slice, a part of a krap, the krap constituting the entire quantity of metal to be removed from any one side or surface of the object.

Fig. 654 represents a planing-machine having two slide-rests on one carriage, each slide-rest being provided with its traverse screw, as seen in the Figure. This is an ordinary arrangement of planing-machines for the convenience of making them capable of planing two articles at one time on the table; and of planing two surfaces or portions of the same article at one time, although the two surfaces may be at different heights above the planing-table. Both slide-rests are used at one time through both traverse screws being rotated at one time by the teeth wheels and feed-rod; but if only one slide-rest is to be used, the necessary disconnection is easily effected. While preparing the machine for planing, either of the slide-rests may be quickly moved along to any desired place by the handle, which fits both the screws' square ends. To plane a surface so that it shall be at some stated angle with the table, one of the slide-rests may be fixed at the angle required; the slide-rest on the left of this Figure (654), is shown to be in position for this sort of planing. In order to accurately apply the tool of any planing-machine to the work for taking off a slice, or what is termed a cut, whose thickness shall be exactly that which is intended, the vertical traverse screw, shown in Fig. 653 by V T, must be slowly rotated until the tool-point is at the exact height, the rotation being easily managed with the hand-wheel on the upper end of the screw. Planing-machines which are specially intended for planing with vertical or oblique traverses, are provided with slide-rests having screws of suitable length for their work, and all are capable of being worked by the same feed-rod that actuates the horizontal traverse. A planing-machine having a vertical traverse gear of this sort, has a circular box on the vertical screw, containing some of the gear, instead of a hand-wheel, and the box is made to serve as a wheel by fixing in four handles.

In addition to the general arrangements now described, which belong to planing-machines of every size and class, it is necessary to briefly mention here that some of the large machines are each provided with two carriages, having two slide-rests on each carriage; some are also furnished with a couple of slide-rests to each standard, for planing surfaces at right angles, and at other angles to the table. We now proceed to consider the accessory apparatus which are indispensable to all sorts and sizes of planing-machines, for attaching and adjusting to planing-tables, objects possessing a great variety of forms.