The steel or iron surface may be turned with the graver and flat tool, employed in much the same manner as on the cylinder, the tee of the rest being placed parallel with the work. Those of small diameter, and collars or shoulders upon cylinders, when reduced to shape by separate cuts of the graver or triangular tool, may then be conveniently turned flat and smooth with the cutting side of the latter. The triangular tool when used for this purpose is held about radially, supported on any one of the angles or cutting edges of the shaft, which indents the tee, and is applied to the work with its side nearly coinciding with the surface to be turned, figs. 477 - 479. By slightly twisting the handle from right to left, fig. 479, the upper of its three cutting edges engages in the surface; the vertical angle of the face of the side cutting edge being then nearly that of the chisel upon softwood.

The triangular tool is so effective for turning iron and steel that it is constantly employed upon flanges, collars, and surfaces, such as are found in the illustrations on page 346; it cuts very freely, but is as easily controlled, removing coarse or fine shavings as the vertical inclination of the cutting face, fig. 479, allows the side edge more or less penetration. The variation from coincidence between the work and the face of the triangular tool, may also be diminished or increased during the progress of the cut, by simply varying the twist given to the handle; with the effect, that the metal shaving, analogous to that removed by the softwood chisel, may be made to pass gradually to and from either condition of thickness or thinness, during the process of its removal. Secondly, owing to the slight curve to which the sides of the tool are ground lengthwise, shown on an increased scale fig. 478, a trifling alteration in the horizontal angle at which the shaft is held to the work, will transfer the point of cutting contact to any required spot between the surface and the tool. This permits the cut to be either commenced towards the centre of the surface, and led thence continuously to the margin, or to be carried from the margin in the reverse direction, without the necessity for shifting the position of the shaft of the tool, lengthwise; while it also enables the edge of the tool to be exactly directed upon any particular spot requiring correction.

Fig. 477. Fig. 478. Fig. 479. Fig. 480.

Section III Manipulation Of The Hand Tools Upon Su 400310

In practice, the iron surface while in process of turning, requires frequent testing by means of a steel straight-edge, applied across its center; the narrow surfaces forming the faces of flanges or collars upon cylinders, in like manner are tested by a straight-edge, then, usually one limb of a steel square, the edge of which is held across them; the rectangle of the square, also determining the correctness of the angle the surface forms with the cylinder. The surface may be continued quite into the internal corner, by the longest or most pointed cutting side edge of the tool, fig. 443; only the extreme point of the triangular tool then arrives at the cylinder, and need not cut into it, nor other finished portions of the work. The corner is completed by finishing its portion of the surface, and the abutting end of the cylinder, concurrently; the tools appropriate to either, being exchanged from time to time as required.

Brass surfaces are reduced, first by separate cuts with the router or sometimes with the graver, but ground to a suitable angle; and are then turned true and smooth with the flat tool, used and held after the same manner as on the cylinder. The tools are supported on the tee of the rest, placed close to and parallel with the surface for the heavier cutting, and upon the arm rest, as in hardwood turning, with the tee parallel with the mandrel, for lighter works and for finishing.

Small surfaces, edges and collars, may be turned with the point tool held underhand, a narrow portion at a time from the margin towards the center; the edge is placed in contact with the surface, the back of the tool lying flat on the rest, and it is made to cut by tilting the tool towards the work, and by pressure. The square tool fig. 458, is also largely used for turning and finishing brass surfaces of small size, flanges and edges, and upon the armrest, for internal work; it is held a little underhand and is otherwise employed, fig. 480, in exactly the same manner as the triangular tool for iron; which tool it closely resembles in all particulars save that of section. Both tools are thoroughly efficient, but only, when each is employed upon the respective materials to which their cutting angles are suitable.

Brass and gunmetal surfaces, more especially those that are thin in proportion to their diameter, are far more liable to the formation of striae than the cylinder; the same precautions already explained, have to be more carefully observed for their prevention. The flat tool is held with great firmness, whether supported on the tee or the armrest, the tool and the hands as in the horizontal manner, with only a narrow portion of the cutting edge in contact with the surface. The cutting edge is not allowed to remain more than a moment strictly quiet at the same elevation during its traverse, and the one end is frequently allowed the most penetration, just sufficient for the opposite end to escape cutting. The finishing tools are also barely allowed to touch the surface of the tee, by the partial interposition of the thumb and forefinger upon either side, the fingers, rather than the tool being pressed on the tee. The armrest, used precisely as in hardwood turning, the end of the tool surrounded and supported by the fingers of both hands is still more efficacious in aiding the absorption of vibration, and is constantly used by the brass turners for surface and internal turning. The vibration of thin surface works, may also be considerably reduced by judicious chucking; when the thin plate becomes to some extent incorporated with the more solid surface chuck, to which it is attached by clamps, screws, or cement, as already described.

The finished turned surface in iron or brass serves as a guide to the flat file, when that is used to obtain increased smoothness; - the safe edge being turned towards any cylindrical portion; - and the file, held in the right hand, is retained in contact with the surface by the ends of all four fingers of the left hand pressed upon its flat side. The contact of the smaller files upon light work, is sufficiently ensured by the forefinger of the right hand which holds the handle, being stretched out along their sides. The stroke of the file is always a tangent to the circle it covers on the surface, but the vertical inclination at which its strokes are given, is frequently varied to cause the different strokes to cross and correct each other's work; the object and necessity for which, have been already referred to in the second volume.