To plane, signifies to produce a plane surface or surfaces. The original mode adopted by engineers for producing a plane surface, consisted in first using a planing chisel and hammer to roughly reduce the metal to proper dimensions for being completed with rough files and smooth ones. If a piece of work happened to be cast or forged with dimensions but little greater than the intended finished dimensions, the article was treated as it is now, being first ground on a stone, to remove the hard exterior, and next finished with rough or smooth filing, the precise amount of filing depending on the dimensions desired.

A plane surface belonging to any article is always relative, the surface cannot exist without being parallel to another plane which is in the same article; and if the object is a parallelopiped, any two opposite plane surfaces of the object are parallel to each other; but if it is a rectangular and taper key, or other object with slant sides, any selected slant surface may be a plane, but it cannot be parallel to its opposite slant side, although it is parallel to an imaginary plane in the object, existing at some stated distance from the slant surface. Through this parallelism of an object's plane surface to some other plane in the object, arises the necessity for considering the particular place of a plane surface which is to be produced on the object.

The production of any desired plane surface is the exposition of it; the plane exists in the metal beneath the rugged exterior, and is exposed to view as soon as sufficient metal is cut off, the precise quantity removed depending on the distance of the desired plane from the rugged surface. The planing of the object therefore consists in producing the hidden plane, and its place should first be determined and indicated, before it is produced and exhibited.

The original mode of determining the place and position of a plane in a piece of work, consisted in looking steadily at it and imagining the plane while looking; therefore, if one rough surface of the article required a sixteenth of an inch slice to be cut off, to attain the desired dimension, the operator decided that the plane he desired to produce existed at a sixteenth of an inch below the rugged exterior, and if the exterior were parallel to the hidden plane, he decided that the surface should be equally reduced, and would not cut off more than a sixteenth from any part of the surface.

As soon as the place and position of the hidden plane is determined, its boundaries also can be determined, because they are in the piece of work, and they may be plainly indicated to the eyes of an observer by means of lines, because the boundaries of planes are lines. Formerly, these lines were mere abstractions, which the operator conceived to exist on the piece of work while he looked at it, and he chipped or filed the piece until it was reduced to the places where he imagined the lines to exist. This is not very difficult to do, if the surface being cut is only a few inches across, and, at the present time, small surfaces are frequently planed by working to abstract lines in this manner; but the more mechanical and proper mode of planing now practised, consists in first indicating the boundaries of the plane, by marking lines upon the surface of the article, whether it is very small or very large. Consequently, planing, as now performed, is intimately related to this marking of the lines, which is termed lining.

The first step in tool-making should consist in making steel parallelopipeds, such as short straight-edges and small surface blocks, because all finishing of engine-work depends in some way on planing, and all planing depends on straight-edges. A beginner in machine-making should commence by attempting to make a tool of some sort that is intended for use afterwards; not merely to practise on something which he intends to throw away, or on something that is either too large, too small, or otherwise unfit to become a tool. If he knows he is merely practising, he is much more liable to become careless and spoil the work. If the beginner is to make a tool by means of planing, it should be one intended to have plane surfaces, and it is now presumed that he has bought or has made such tools as scribers, callipers, and short straight-edges, which are treated in the second and third chapters. Being thus provided, he should commence planing by making a small pillar-table of cheap granular steel, similar in shape to that shown by Fig. 615. This is a solid cylinder of ordinary rod-steel, about three inches long and two inches thick. If he is quite a novice, it is advisable for him to devote his attention to specially producing only one of the cylinder's planes, which will enable him to make a surface-table; but when he has advanced a little, his object should be to specially plane both ends of the block, and to make both the planes parallel to each other; this is more difficult, and produces a parallel block that will be more useful than if the implement had only one plane surface. Whether the work is to have one plane or two, it is proper to reduce the two ends without using a lathe or planing tool of any sort, except chisels and files, unless the piece is much longer than necessary; if so, it can be lathe-turned, reduced with a planing-machine, or cut while hot on an anvil, until about an eighth of an inch remains at each end for chipping and filing. The curved surface of the lump needs no reducing, and remains as it was when first cut from the rod shown in Fig. 618.

When the piece is forged, or otherwise prepared, the first planing consists in reducing one end of it until at right angles to the length of the cylinder, but without taking off any stated quantity. In order to make this end square to the length of the piece as required, an el-square is necessary, which is frequently applied during the rough filing, as shown in Fig. 619. This squaring is of little consequence, except for appearance, because the block is not to be a parallelopiped; so that the operator devotes his principal attention to producing the plane surface without precisely determining its relative position.