Angles 70° to 90°. - Figures generally the same as the tools for hard wood.

The turning-tools for brass are in general simple, and nearly restricted to round, point, flat, right and left side tools, parting tools, and screw tools; they closely resemble the hard-wood tools, except that they are generally ground at angles of about 60° or 70°, and when sharpened it is at an angle of 80° or 90°; some few of the finishing or planishing tools, are ground exactly at 90°, upon metal laps or emery wheels, so as to present a cutting edge at every angle and on both sides of the tools.

It is not a little curious that the angles which are respec-tively suitable to brass and to iron, are definitively shown to be about 90 and 60 degrees. For turning brass, a worn-out square file is occasionally ground on all sides to deprive it of its teeth, it is used as a side tool, and is slightly tilted, as in fig. 408, just to give one of the edges of the prism sufficient penetration; but applied to iron, steel, or copper, it only scrapes with inconsiderable effect. A triangular file, fig. 409, similarly ground, cuts iron with great avidity and effect, hut is far less suited to brass; it is too penetrative, and is disposed to dig into the work. It appears indeed, that each different substance requires its own particular angle, from some circumstances of internal arrangement as to fibre or crystallization not easily accounted for.

Figs. 408.

Section IV Turning Tools For Brass 20040

409.

Section IV Turning Tools For Brass 20041

410.

Section IV Turning Tools For Brass 20042

A stout narrow round tool, fig. 392, in a long handle, serves as the gouge or roughing out tool for brass-work, others prefer the point, fig. 385, with its end slightly rounded, which combines, as it were, the two tools with increased strength; a small but strong right side tool 382, is also used in rough-turning; the graver, figs. 411 and 412, although occasionally employed for brass, is more proper for iron, and is therefore described in the next section.

The wide finishing tools should not be resorted to under any circumstances until the work is roughed out nearly to the shape, and reduced to perfect concentricity or truth, with narrow tools which only embrace a very small extent of the work.

It is the general impression that in taking the finishing cuts on brass it is impolitic, either to employ wide tools, or to support them in a rigid solid manner upon the rest, as it is apt to make the work full of fine lines or striae. This effect is perhaps jointly attributable to the facility of vibration which exists in brass and similar alloys, to the circumstance of their being frequently used in thin piees on the score of economy, and to their being rotated more rapidly in the lathe than iron and steel, to expedite the progress of the work.

When a wide flat tool is laid close down on the rest, and made to cut with equal effect throughout its width, lines are very likely to appear on the metal, and which if thin, rings like a bell from the vibration into which it is put; but if the one corner of the tool penetrate the work to the extent of the thickness of the shaving, whilst the other is just flush with the surface, or out of work, the vibration is lessened, and that whether the penetrating angle or the other move in advance.

The brass turner frequently supports the smoothing tool upon the one edge only, and keeps the other slightly elevated from the rest by the twist of the hand, which thus appears to serve as a cushion or spring to annul the vibrations, fig. 410 shows about the greatest inclination of the tool. Some workmen with the same view interpose the finger between the tool and the rest, in taking very light finishing cuts. The general practice, however, is to give the tool a constant rotative shuffling motion upon the supported edge, never allowing it to remain strictly quiet, by which the direction of the edge of the tool is continually changed, so as not to meet in parallelism any former striae which may have been formed, as that would tend to keep up the exciting cause, namely, the vibration of the metal. The more the inclination of the tool, the greater is the disposition to turn the cylinder into small hollows.

Some workmen burnish the edges of the finishing tools for brass, like the joiner's scraper, or the firmer chisel used in softwood turning. On account of the greater hardness and thickness of the edge of the tool, it cannot be supposed that in these cases any very sensible amount of burr or wire edge is thrown up. The act appears chiefly to impart to the tool the smoothness and gloss of the burnisher, and to cause it, in its turn, to burnish rather than cut the work; the gas-fitters call it a planishing tool, but such tools should never be used for accurate works until the surface is perfectly true and smooth.

The hard-wood and brass turners avoid the continual necessity for twisting the lathe rest in its socket to various angular positions, as they mostly retain it parallel with the mandrel, and in turning hollow works they support the tool upon an armrest; this is a straight bar of iron, which resembles a long-handled tool, but it has a rectangular stud at the end, to prevent the cutting tool from sliding off.

The position of the arm-rest and tool, as seen in plan, are therefore nearly that of a right angle; the former is held under the left arm, the latter in the right hand of the workman, the fore-fingers of each hand being stretched out to meet near the end of the tool. This may appear a difficult method, hut it is in all respects exceedingly commodious, and gives considerable freedom and choice of position in managing the tool, the advan-tage of which is particularly felt in guiding the first entry of the drill, or the path of the screw-tool; and in brass work it likewise renders the additional service of associating the tool with the elastic frame of the man. But when particular firmness and accuracy are required the tool should be supported upon the solid rest as usual.