For some purposes, axles and shafts require their keys to be solid with their respective portions, instead of being separately made and fitted into key-ways. A key which is solid with an axle, is a key-ledge, and two such ledges may be required on one spindle, both key-portions or ledges being situated on a minor axis, one ledge at each end, which arrangement is usually termed, opposite each other, or, at opposite sides of the axle. Spindles or shafts of this class in general should be of steel, in order to possess a solid close metal which is nearly devoid of fibres, that no cracks may exist whose lengths are parallel to the lengths of the shafts. If such cracks exist in any part of a key-ledge, the strain on it during use would probably separate it from its axle.

A piece of steel which is to be formed into a spindle having two key-ledges, is denoted by Fig. 815. The accurate shaping of such a piece, previous to forming the keys, consists in lathe-turning the two small ends and also the larger portion between. The diameter to which this part is turned is equal to the required distance between the two extremities of the two intended ledges, the distance being measured across the centre of the spindle. The shoulders of this thick part are also smoothly turned to make them square to the spindle's length, and to admit scribed lines. The piece being turned to proper dimensions becomes ready for scribing, which indicates the places of the two ledges to be formed. This scribing is effected by placing the spindle upon two vee-blocks in a position similar to that of the spindle shown by Fig. 828. While on such blocks it is packed up, if necessary, to place it parallel to the table-face, and a scriber-block is then employed to mark the places for both key-ledges at one operation, the smoothly turned shoulders being also scribed while the spindle still remains in position on the blocks. The lines which are thus scribed for one key-ledge, are those seen in the Figure (815), consequently, a similar set of lines are marked also upon the further side of the object, because two ledges are required. The middle line of each set is a primary which should be lightly dotted, in order that circles may be scribed from it in the event of the lines which show the width of the ledge becoming erased by filing or other means.

When the places for the two key-ledges are thus shown, the work proceeds by gripping one end of the spindle in a vice and supporting the other end on a screw-prop. While in this situation grooving chisels are used to form grooves along the superfluous steel, the lengths of them being parallel to the lengths of the intended ledges. The superfluous ridges which are produced by such grooving, are now removed with planing-chisels. These chisels are employed until the thick intermediate portion of the spindle is smoothly chipped and the two ledges are produced as required ; after which the object is finished to the exact shape and dimensions intended with rough files and smooth ones.

The uses of centre-finders to mark places for key-grooves, are illustrated by Figs. 816, 817 and 818. By means of a centre-finder the minor axis of a cylindrical shaft-end is easily indicated by placing the pedestal of the tool to the shaft-side with the blade extending across the extremity, and marking a line with a scriber. The position of the centre-finder during such an operation, is seen in Fig. 817, a plan of the tool and the shaft-extremity being shown by Fig. 816, in which Figure the blade's edge is seen to coincide with the shaft's minor axis as desired.

A centre-finder will also easily show the place of a centre-line across the face of a wheel-boss or a lever-boss. While using the tool for such a purpose, it may be situated either as in Fig. 818 with the pedestal nearest the lever-arm, or situated with the pedestal at the opposite side of the boss, the blade being therefore in this case over the lever-arm.