The curved junctions of a boss are shaped while the lever or bar is fixed with its boss-faces parallel with the slotting-table, as when the narrow sides of its arm are being shaped. Considerable care is required during shaping, to make the junction to a proper curve, to make it to a proper depth, and to nicely smooth it, that no ridges may be noticed after it is machined.

For the purpose of avoiding unnecessary trouble while a boss is between the conical pivots of a shaper, or on an arbor-chuck of a slotting-machine, the shaping of the boss by means of its rotary motion, should terminate at the commencement of each curved junction of the boss, all the superfluous metal at the junction being left untouched. Both bosses of the lever should be thus treated previous to commencing the shaping of the intermediate part or arm. The shaping of the straight arm, if effected with a shaper, is performed while it is fixed with its narrow side upwards, both the bosses and junctions being now finished. When a slotting-machine is employed for the narrow sides of the arm, the shaping of the straight portion, and also the shaping of the curved junctions, is done while the boss-faces are parallel with the table, and the narrow sides are parallel with the slide-rest traverse which is parallel with the machine-front. Whenever a lever or bar is required to present a special smooth and neat appearance, the bosses and junctions should be entirely finished previous to finishing the straight part of the arm. Supposing that the entire outer surface of a lever is to be machined, the bosses should be entirely reduced and finished, and the junctions also finished, previous to finally smoothing the arm's narrow sides; and all levers and bars that may require a great amount of metal to be removed, should have the straight parts of their arms roughly reduced before finally smoothing the junctions.

Curved junctions should be shaped while the levers or bars are in the same positions on the table in which they were during the shaping of the arms' narrow sides; consequently, the fixing of the lever for shaping the straight part is the fixing for shaping the junctions, no change being necessary. The straight mid-part of the arm is that which should be first roughly reduced, the reduction being continued till it is very near the specified dimensions. The two junctions which are now in front of the cutting tool should next be reduced, the entire quantity of metal being removed, and the curved surfaces carefully and finally continued from the finished surfaces of the bosses. These two curved parts being completed, leaves the straight part of the arm yet rough; and to finish the entire narrow side of the lever it is now carefully advanced to a sharp smoothing tool for taking off a thin piece along the arm. For this last slice a tool having a broad cutting edge must be used, and its edge made to only just lightly touch the finished extremity of the curved junction; when thus adjusted, the traverse of the lever is put into action, and the smoothing completed. For a finishing slice of this sort it is not necessary to cut off a portion along the entire length; about half the length of the arm is quite sufficient; and to prevent the tool entering the metal too far at the middle of the lever, it should be shifted a small quantity to cause the tool to leave the metal at the proper place. The middle of the surface being shaped may be, for any bar or lever, rather convex, instead of rather concave; so that after two junctions at one side of a lever have been finished, the tool which finishes the straight part may be made to take off two minute slices, one from each junction, and both towards the middle of the lever, which process will produce the convex form referred to.

After one narrow side has been finally smoothed, the lever or bar is put upside-down, and again fastened with its length in the same position as before. In this condition the other narrow side and its two junctions can be reduced and smoothed by the same means that were employed for reducing the side now finished.

The class of tools which will quickly remove the thick mass of metal at the junctions are the vee-point tools shown by Figs. 787, 788, 793, and 794; some of which tools have ends slightly bent, to make them resemble corner tools of planing-machines. These pointed tools are only necessary for large bosses, when it is requisite to cut off a great quantity of metal; and the tools are caused to form a few ridges at the place of the intended curved surface, by gradually advancing the lever to the tool by rotating the traverse screws. The junction being thus roughly formed with pointed tools, is made ready for being finished with a springy tool, the cutting edge of which is curved and convex, to suit the curved shape of the junction. Springy tools for this purpose are represented by Fig. 792; with the difference of a tool having a curved edge being keyed in the slot, instead of the one shown in the Figure, whose edge is nearly straight, this form of tool being required for smoothing the outside of a boss.

A small lever or bar may have its junctions entirely shaped with tools having broad cutting edges; a springy tool being used for polishing, in the same manner as for larger work. Any such curved surface, small or large, should be reduced and finished with tools which have as broad edges as the machine will permit; by using broad tools, the cutting edges of which are nearly as long as the extent of the junction, all the shaping of it is executed with very little rotation of the traverse screws, by reason of a comparative great length of the cutting edge being at one time in contact with the metal.

When it is requisite to form a junction to some exact curve of a desired length and shape, sheet-templates are used, the shapes of which are similar to the shapes required for the curves in the objects in progress. Concerning templates, refer to pages 244 and 245.