A small three-cornered broach, which is to be fixed in a wood handle resembling a file-handle, is made of an old small saw-file, the file teeth being ground off with a grindstone, and the tool finally smoothed on an oil-stone. A five-cornered broach is made by first forging a cylindrical broach with a square head and cylindrical stem of proper length for its use, and producing the pentagonal shape with planing, or with filing, if the tool is small. A taper half-round one is first forged conical, and also lathe-turned conical, and the half-round character produced by planing off half the cone. Both five-cornered ones and half-round ones are also made by forging them in their respective shapes, and finishing them with filing, without any other planing process. Taper half-round ones are thus easier finished than taper five-cornered ones. The shaping of a five-cornered broach on an anvil is performed with pentagonal tools; a couple of pentagonal top and bottom tools consist of a top tool which has a broad vee-gap, and a bottom tool that has a three-sided gap. The tools required for shaping a half-round taper broach on an anvil, are, an ordinary flatter, and a bottom tool having a half-round taper gap.

Fluted broaches are those having grooves with curved bottoms, which are termed flutes. A fluted broach may have one, three, five, or seven flutes, and the forging for either class is the same, all such tools being forged either conical or cylindrical, and afterwards fluted while cold. Those that are to be used with crank braces and swing braces are short, having square heads immediately adjoining the fluted portions. Fluted ones for lathes are provided with long cylindrical stems, each stem having a square head at the outer end. A broach of this sort is shown by Fig. 596, the long stem being necessary to reach the poppet-pivot without bringing the poppet-head too near the lathe-carriage. These broaches require to be carefully straightened and equally hammered at the conclusion of forging, while the tool is equally heated along its entire length; all the particles of a tool are thus equally condensed, and it is not so liable to bend during turning and hardening as it is when improperly hammered.

The lathe-turning of a long broach commences by first taking off a small quantity that is only just sufficient to make the tool rotate truly along its entire length while on the pivots; the work is next heated to dull red, and hardened by dipping it while its length is vertical; it is next heated with only a very little blast, and buried in cinders or powdered charcoal till cold, to soften it. During this heating, the tool should lie on a flat bed of small cinders, to prevent it bending while soft; and it is also properly supported while softening among the charcoal powder. The next day the lathe-turning of the broach is resumed without straightening it, and when another sixteenth has been turned off it is again softened, if the steel appears to be harder in some of its parts than in others, or if the entire piece is a hard brittle metal; if found to be brittle, it should be softened two or three times without charcoal. A large broach resembles a large screw-tap in being expensive; consequently, one or two preliminary hardenings and softenings should be given to every such tool if it presents the slightest appearance of being too brittle or too solid.

The particular character and diameter of a broach is determined during turning, whether taper or parallel; if to be taper, it is turned to the form of a straight-sided cone along the entire length of the cutting part; and if the broach is to be what is called parallel, it is also slightly tapered along the entire length of its cutting portion, in addition to a short bevel at the point, for entering it to the work to be broached. A broach slightly tapered is always easier to use and makes smoother holes than one which is exactly parallel, and it is seldom necessary to broach a hole so that it shall be parallel; consequently, the small amount of taper referred to is advisable. After lathe-turning, neither the extreme diameter of the parallel portion, nor the extreme diameter of the point of a broach, must be altered by filing; each one is therefore turned to its precise thickness required, previous to commencing the fluting.

The fluting of broaches is effected by the same means as for fluting taps, and the flutes are of similar shapes for both. Straight lines along the intended cutting part of each broach should be marked while in a lathe, by moving to and fro a pointed tool, and the shape of each flute also requires marking on the flat extremity of the small end, as described for marking taps. The centre recesses also are properly shaped and used for supporting each broach, to allow it to be rotated during the fluting process; and a slotted holdfast is useful for gripping the stem of a broach while being fluted, if the one in progress has a stem.

A broach having a stem which is smaller in diameter than the cutting part of the implement presents no obstruction to the free movement of the fluting tool along the entire length of the intended teeth; such broaches may be placed for fluting on vee-blocks, instead of between poppets. Those having stems are also easily fluted while in a lathe with the to-and-fro movement of the lathe-carriage referred to.

Short ones are sometimes made entirely without any cylindrical stem, having a square head which is as thick as the intended fluted part, and close to it. A broach thus made must have a groove formed around the thick part, if it is to be fluted by planing; the situation of this groove is at the junction of the head with the remainder, and the bottom is curved, to avoid angular corners. A groove of this sort is made with a proper grooving tool during the turning, and its depth is a little deeper than the depth of the flute to be made, the groove being necessary to provide a space at the extremity of the tool's travel while planing.