Note A. Q, page 983.
The a works of the lathe and planing-machine frequently present angles or rebates, chamfers, grooves, and under-cut lines, which require that the tool should be bent about in various ways, in order that their edges may retain as nearly as possible the same relations to all these surfaces, as the ordinary surfacing tools figs. 431 and 432 have to the plane a b. For instance, the shaft of the tool 431, when bent at about the angle of 45 degrees, becomes a side cutting and facing tool, as shown in plan in fig. 434, in elevation in 435, and in perspective in 436; and in like manner, the cranked tool 432, when also bent as in 434, becomes 437, and is also adapted to working into angular corners upon either face.
Mr. Nasmyth's tool gage, shown in elevation in 438, and in plan in 439, entirely removes the uncertainty of the angles given to these irregular bent tools: for instance, when the shaft of the tool is laid upon the flat surface and applied to the iron cone c, whose side measures about 3° with the perpendicular, it serves with equal truth for s, the tool for surfaces; p,f, the side-cutting tools, used also for perpendicular cuts and fillets; and u for undercut works. In applying tools to lathe works of small diameters, it is necessary to be very exact, and not to place them above the center, or they immediately rub; and as this soon occurs with tools having so small an angle, it appears desirable to make the cone gage for small lathe works of about twice the given angle, and to mark upon the cone, a circle exactly indicative of the height of center; the tool can be then packed up to the center line, with one or two slips of sheet iron, to be afterwards placed beneath the tool when it is fixed in the lathe rest. In small hollow works, the most lasting of the crank-formed tools, are entirely inapplicable, indeed so much attention is required to prevent the tool from rubbing against the interior surfaces, that the ordinary angles cannot be employed, and the BRUNEL's cutter bar. triangular cutter bar. 535 cone gage ceases to be useful, but in every other ease it should be constantly resorted to; the additional thickness a, is required to make it applicable to the crank-formed tools.*
Fig. 440, represents a cutter introduced in the Block Machinery at Portsmouth, to lessen the difficulty of making and restoring the tools, far turning the wrought-iron pins for the sheaves; it consists of a cylindrical wire which, from being ground off obliquely, presents an elliptical edge; the tool is fixed in a stock of iron, terminating in an oblique hole, with a binding screw. The tool, when used for iron, in the "pin turning lathes," was made solid, when used for turning the surfaces of the wooden shells, in the "shaping engine," it was pierced with a central hole; the latter could only facilitate the process of sharpening, without altering the character of the edge, which continued under the same circumstances as when solid.
About sixteen years back, the author made for his own use, a tool such as fig. 440, but found that with rough usage the cutter was shivered away, on account of its breadth, and he was soon led to substitute for the solid cylinder, a triangular cutter, the final edge of which was slightly rounded, and placed more nearly perpendicular, in a split socket with a side screw, as in fig. 441. The strength of the edge was greatly increased, and it became, in fact, an exact copy of the most favourable kind of tool for the lathe, or planing-machine, retaining the advantage that the original form could be always kept, with the smallest expenditure of time, and without continually re-forging the blade, to the manifest deterioration of the steel from passing so frequently through the fire; it being only requisite to grind its extremity like a common graver, and to place it so much higher in the stock as to keep the edge at all times true to the center.
* The general similitude between some of the author's figures, 429 to 439, (engraved in Jan. 1840), and part of those in Mr. James Nasmyth's article on Tools, in Buchanan's Mill Work (published in Dec 1841), is solely due to their being each indebted to the some individual (namely, to Mr. Joseph Clement), for the general theory advanced, and which associates the principles of machine tools for metal that are of comparatively modern date, with those of cutting tools generally, even of the most primitive kinds.
A right and a left hand side tool for angles, the former seen in figs. 442 and 443, were also made; the blade and set screw were placed at about 45°, and at a sufficient vertical angle, to clear both the inside of a cylinder of three inches diameter, and also to face the bottom or surface. These side tools answered very well for cast iron; but fig. 441, the ordinary surfacing tool, is excellent for all purposes, and has been employed in many extensive establishments.*
In turning heavy works to their respective forms, a slow motion and strong pointed tools are employed; but in finishing these works with a quicker rate of motion, there is risk of putting the lathe in a slight tremor, more particularly from the small periodic shocks of the toothed wheels, which in light finishing cuts are no longer kept in close bearing as in stronger cuts.
Under these circumstances, were the tools rigid and penetrative, each vibration would produce a line or scratch upon the surface, but the finishing or hanging tools, figs. 444 and 445, called also springing tools, which are made of various curves and degrees of strength, yield to these small accidental motions. The first resembles in its angles the rest of the tools used for brass, the second those for iron, their edges are rectilinear, and sometimes an inch wide. The width and clasticity of these finishing tools, prevent them acting other viae than as scrap for removing the slight superficial roughness, without detracting from the accuracy of form previously given. In a somewhat similar manner the broad hand flat tool, rendered elastic by its partial rapport, as in fig.410, page 521, is frequently used for smoothing brass works, and others turned with the slide rest.