The planing of the port-faces and other plane surfaces of cylinders is performed after the cylindrical surfaces are bored, and, in some cases, also after the outer circular surfaces are lathe-turned. The port-faces, the slide-jacket faces, the faces of the lugs, and all other faces which may be solid with a cylinder, require to be parallel to the major axis of the cylinder, although such surfaces may be inclined at various angles to each other. The first step, therefore, towards preparing a cylinder for a planing-machine, consists in indicating the place of the major axis. This is done by first tightly fixing a bar of wood or iron at each end of the bore, and next marking the centre on each piece, after the centre has been accurately found with a compasses, or, if the cylinder is large, with a radius gauge of suitable length. Such bars, when used for centring, are termed enders, or extenders, and the centre dot on one ender indicates one extremity of the axis, the other extremity of the axis being shown by the dot on the other ender at the opposite end of the cylinder. Through these two dots being properly placed, the adjustment on a planing-table to produce planes that shall be parallel to the bore, or axis, is easily effected.

In some cases it is convenient to fix and plane two small cylinders at one time on the table, in order to produce a pair of cylinders having the same shape and dimensions. Two cylinders situated for this purpose are seen in Fig. 756. Each one is provided with two enders, for indicating the axes, and of the four enders two are shown, one in each cylinder. When two cylinders are to be thus planed, the axis of each one must be placed parallel to one of the gauge-lines along the table, and both ends of both axes must also be put at the same height above the table; consequently, the two axes are portions of one straight line extending through both cylinders as soon as they are accurately adjusted, but not till then. This double adjustment can be easily effected by means of plates and wedges beneath the cylinder and on the table, in conjunction with a scriber-block. A scriber-block in use for this purpose is denoted in the Figure (756) ; the bottom edge of this block is quite straight, sharp, and also of sufficient length to allow it to be quickly and accurately placed in line with one of the gauge-lines along the table, the line selected being as near as convenient to the axis of the cylinders. By thus repeatedly placing the block at each end of the cylinder with the scriber-point near the centre, and the bottom edge of the block on the gauge-line, the amount of wedging requisite is ascertained, and effected accordingly.

There is also another mode of adjustment for cylinders, which is especially suited to large ones of four, six, or eight feet in diameter. This adjustment is accomplished by the aid of the table's short gauge-lines. By this method the scriber-block is put very near to the enders, and the point is repeatedly applied to both centres during adjustment of the cylinders, until they are placed equi-distant from the table. The scriber-block is now taken from the axis and put near the turned or bored flange, the straight bottom edge of the block being also put exactly to some part of a short gauge-line. While the block thus stands, its scriber-point is raised or lowered to make it just touch the finished surface of the flange, and while the point remains at this height the .block is removed and put to the opposite portion of the same flange, being also careful to adjust the bottom of the block to some part of the same gauge-line on which the block before stood. This second placing of the block, will determine whether the flange is parallel to the line, and, consequently, will show whether the cylinder's bore is parallel to the table's length, as required. If it is found to be not in the desired position, the cylinder is shifted by means of the poppet-screws in contact, and the scriber-point is again applied to the flange as before, to ascertain what further adjustment is necessary.