Angles 60 to 90 deg. - Figuers generally one-sixth the full size.

The triangular tool is one of the most effective in turning these metals, as was adverted to at page 521; the triangular tool is also used by the engravers and others for scraping the surfaces of the metals, and it is then applied nearly perpendicular, or as a penknife in erasing; but when the triangular tool is placed nearly as a tangent against the inner or outer edge of a ring or cylinder, as in fig. 409, it seems almost to devour the metal, and instead of scratching, it brings off coarse long shavings. In turning the flat sides of the ring, the face of the tool is placed almost in agreement with the plane to be turned.

The graver, which is also an exceedingly general tool, is a square bar of steel ground off at the end, diagonally and obliquely, generally at an angle of from 80 to 50 degrees. The parts principally used are the two last portions of the edge close to the point, and to strengthen the end of the tool a minute facet is sometimes ground off, nearly at right angles to the broad chamfer, or principal face.

The proper position of the tool, in turning a cylinder, will be most readily pointed out by laying the chamfer of the tool in exact contact with the flat end of such cylinder; it will be then found that one of the lateral angles of the tool will touch the rest, and the obliquity in the shaft of the tool, would be the angle, at which the graver is ground, instead of which it is held square and slightly elevated above the horizontal portion, as shown in fig. 411. The graver is rotated upon the supporting angle which sticks into the rest, much the same as the edge of the triangular tool; in fact, the two tools, although different in form, remove the shaving in a very similar manner.

In using the graver and other tools for the metals, it is the aim to avoid exposing the end of the tool to the rough gritty surface of the material. This is done by cleaning the surface, especially the extreme edge, with an old file, and beginning at that edge, the work is at one sweep reduced nearly to its required diameter by a wide thin cut, which may be compared with a chamfer, or a conical fillet, connecting the rough external surface with the smooth reduced cylinder. Therefore after the first entry, the point of the tool is buried in the clean metal below the crust, and works laterally, which is indeed the general path of pointed tools for metal.

Section V Turning Tools For Iron Steel Etc 20043

When the graver is used in the turn-bench with intermittent motion, as for the pivots of watches, the axes for sextants, and other delicate works; it is applied overhand or inverted, as in fig. 412, but it is then necessary to withdraw the tool during each back stroke of the bow, to avoid the destruction of the acute point, and which alone is used. The graver, when thus applied in lathes with continuous motion, is only moved on the rest as on a fulcrum, and in the plane in which it lies, rather as a test of work done, than as an active instrument.

The edge of the graver is afterwards used for smoothing the stronger kinds of work, it is then necessary to incline the tool horizontally, to near the angle at which it is ground, in order to bring the sloping edge parallel with the surface. But the smoothing is better done by a thick narrow flat tool, ground at about sixty degrees, the handle of which is raised slightly above the horizontal, as in fig. 413, in order that its edge may approach the tangential position; here also the tool is rotated on one edge, after the manner of the brass tools or the graver.

For many slight purposes requiring rather delicacy than strength, as in finishing the rounded edge of a washer, the flat tool is inverted or placed bevil upwards, as in fig. 414; the lower side then becomes the tangent, and the edge the axis of rotation of the tool, the same as in turning convex mouldings with tin- soft-wood chisel. Indeed, many analogies may be traced between the tools respectively used for soft woods and iron, except that the latter are ground at about twice the angle to meet the increased resistance of the hard metal, and the tools are mostly sustained by the direct support of the rest, instead of resting in great measure against the hands of the individual.