Machine-planing consists in producing a plane by the aid of a machine, in addition to employing some of the means adopted for hand-planing. Strictly speaking, a machine for planing is any machine which produces plane surfaces; but, in this place, the term planing-machine is meant to signify one of a large class that produce planes by means of a horizontal to-and-fro motion, termed, in lengthy language, a horizontal reciprocating rectilineal movement. Small planing-machines, for planing surfaces of only a few inches area, are named shaping-machines, and most of them are actuated by a crank-pin and a connecting-rod which moves the sliding head or tool-head to and fro in the desired path. To this head the cutting-tool is attached, and is moved while the work being cut remains comparatively stationary. This class of machines is represented by the one in the middle of Plate 35.

Large planing-machines are so made that the piece of work to be planed shall move to and fro, but not the cutting-tool. The piece is thus moved by means of a moving table, to which the article is fastened with screw-bolts and plates. The table is provided with planed vee-slides or ridges, that slide to and fro while in vee-grooves of similar shapes, the vee-grooves being formed in the upper part of the bed, which is a heavy fundamental portion of the machine.

Plate 48

Large planing-machines have no motion produced with a crank-pin and connecting-rod, and are represented in Plate 48, which shows all their ordinary arrangements. Of the two machines in this Plate, the one shown by Fig. 653 is the simplest, because it has only one slide-rest; and this portion, together with all the other portions, are named in the Figure. Such machines are of a great variety of sizes, that they may be suitable for planing an area of only about one foot, and for planing one of three or four hundred feet. They are distinguished into sizes by the length, width, and height of the articles that may be planed with them; and if the extreme length of the table's travel in one direction is twenty feet, the machine is said to have a twenty-feet travel. In the Figure the heaviest portion, termed the bed, is seen by its name, and the vee-grooves belonging to it are shown by V G. The vee-slides which fit the grooves are not seen, being under the table, and usually solid with it. In order to move such tables to and fro, several means are adopted. The most general of these consists in employing a step-rack and a step-pinion. This rack is either solid with the under side of the table, or firmly fastened to it, and the teeth of the rack are engaged with the teeth of the pinion, the pinion being in the intermediate space of the bed. To rotate the step-teeth pinion, it is provided with a spindle which is rotated by teeth-wheels, connected to the band-pulleys seen in the Figure at the further side of the machine. Another mode of moving a planing-table consists in using a screw and nut, the nut being firmly attached to the under side of the table, instead of a step-teeth rack, that the screw may be made to rotate in the nut while extending along the intermediate space or gap of the bed. This is the principal or main screw of the machine, and has but one sort of motion, which is a rotary movement around its major axis; consequently, the screw-nut on the screw must move in a path which is parallel to the length of the screw, and the screw is so placed that it is parallel to the planes of the table and its vee-slides. Whatever small quantity of motion the main screw may have in the direction of its length results merely from the small amount of wear of the shoulders.

By whichever of these means the table is moved, the band-pulleys are required to impart the motion; these are worked with leather bands which are driven by the shaft of the factory, and if a main screw is employed to move the table, the pulleys may be at one end of the bed, instead of at the back of the machine. The leather bands are, in many cases, actuated by a power shaft situated above the machine; but the preferable plan consists in providing a shaft beneath the machine, and placing the machine pulleys as low as possible. Such an arrangement involves less danger to workmen, if the pulleys are incased with sheet iron, and the conveyance of heavy pieces to and from the machine-table, is also greatly facilitated.

The to-and-fro motion of the table with the work fixed thereto, and the movement of a cutting tool, in contact with the work, together effect the planing; therefore the means of obtaining this result must be described. Through a planing-machine being required to produce a plane, either of three plans may be adopted ; the piece to be planed may move and generate a plane by its movement, while the tool for cutting remains a fixed point; or the point represented by the tool may move and generate a straight line while the piece of work moves at right angles to the line; or both the tool-point and the piece of work may move, and both generate planes by the movement, the two planes coinciding with each other. Of these three arrangements, the one belonging to the machines here mentioned, is that by which the tool-point is made to generate a straight line across the direction of the table's motion to and fro. This rectilineal motion of the tool is its horizontal traverse or travel, and is obtained by the tool being fixed in a tool-holder and slide-rest which are moved across the table by means of the traverse screw and carriage. Through this screw being supported with shouldered bearings at each end of the carriage, the screw has but one sort of movement, which is a rotary motion around its major axis, similar to the motion of a main screw for moving a planing table. The travel of the slide-rest and tool is therefore effected by rotating the screw in its nut, which is fastened in the slide-rest, the rotation being done by an operator with the handle shown by H. By reference to the Figure it will be seen that the two standards of the machine are those portions to which the carriage is fixed, and this fixing is effected by screw-bolts and nuts situated at the further side of the carriage.