Fig. 609.

Axial Or Simple Plain Turning Part 3 400361

The bead at the base A is first completed by separate cuts made with a narrow chisel, used in the manner described in turning the half bead next the ferrule upon the handle, fig. 608. One side having been shaped, the chisel is turned over, again laid on the top of the bead and twisted in the reverse direction to form the opposite half; these two cuts being in part or wholly repeated, as may prove necessary in gradually reducing the bead to diameter and its two sides to precise similarity of curvature. The under edge of the band B is then turned square with the chisel, presented on its edge as in turning the surface, the one bevil of the cutting edge at right angles to the axis of the work; the tool carefully prevented from cutting to a greater depth, than will rather less than suffice for that of the edge of the band. In working to a copy, a succession of these thin cuts would be made, until the distance from the under side of the band to the under side of the base, is found to agree with that in the original. The width of the band may next be determined by measurement and a series of surface cuts upon its upper edge, after the same manner.

The long curve from B to A is then turned with a wider chisel, in the same manner as the curve of the handle, fig. 608, travelling down hill, the obtuse angle leading, until it arrives in contact with the bead at the base. The chisel lies at an horizontal angle, as that to the right in fig. 339, to place its corners free of the work, and there is therefore a narrow width of the upper end of the curve, immediately under the band, which cannot be reached unless the shaft of the chisel be placed at about right angles, and then not conveniently, from the liability of the acute corner to catch against the edge of the band. To turn this narrow portion, which occurs in all similar curves starting from a shoulder and sloping downwards, the chisel has to be turned over to lie in the position of that on the left fig. 339. So applied on the curve, the chisel is cutting uphill and against the grain; it is therefore traversed as little as possible, being rather held in such a position, that its obtuse corner will just arrive against the shoulder upon the tool being made to cut by slightly raising the handle. The short portion referred to close under the band, would be first turned and the chisel then reversed to continue the shaving to the end of the curve.

Upon a small scale, the curve from the upper edge of the band to the edge of the lower fillet of the astragal, would be entirely turned with the gouge ; that selected, fig. 327, being small and ground to the elliptical cutting edge referred to. The tool is applied lying exactly on its side, its long bevil at right angles to the axis of the work, and in absolute contact with the square upper edge of the band. It then for the first moment cuts by the center of its elliptical edge, but so soon as its traverse commences, the shaft is gently twisted to cause the tool to lie a little less on its side, while traversing the roundest portion of the curve, when it cuts by a part of the edge slightly to the left of the center. As the shaving is continued into the hollow, the gouge is as gradually turned back again so as to be again supported on its side, in which position the tool remains until it arrives at the center of the neck. It is then withdrawn, turned over, and again upon its side with the bevil at right angles to the axis, is applied to the edge of the fillet of the astragal, to turn the opposite half of the curve. The gouge is thrust almost straight forward for the upper part of this curve, after which it is slightly twisted to lie less on its side, while it also receives a slight traverse on the rest, as it meets the termination of the opposing cut.

Upon larger examples, the convex portion of this curve so far as the vertical dotted line, would be more conveniently turned with the chisel; the remainder and the opposite side, with the gouge as described. The obtuse corner of the edge of the chisel would be first applied against the upper shoulder of the band, to turn a short length of the curve for the reasons lately given; the blade would then be turned over, to continue the curve from this so far as the vertical dotted line, the curve being obtained partly by traversing the chisel but more by twisting the shaft as in turning a sphere. The gouge would then be used to continue the curve to the bottom of the hollow; first tracing a portion of that just cut by the chisel, supported on its edge but without cutting, and then as it commences to act, being gradually twisted until it lies on the center of its back when it arrives at the smallest part of the neck. The opposite half of the curve starting from the under edge of the fillet, is in both cases gradually formed by more than one traverse of the gouge, so that guided by measurement, it may determine the distance of the edge of the fillet of the astragal from the base. The width of the complete astragal is then reduced upon its upper edge by the chisel, as with the band, and the position for the under side of the head being found, the curve connecting the two is next turned. This second neck being reduced to the same diameter as the first as measured by the callipers, and the opposing sides of the two hollows turned to precisely similar curvatures.

The edge of B is next turned with the chisel to the diameter and flat curve of the copy, and the round of the astragal and that of the head, the parts remaining for completion, are reduced with the chisel to very nearly their finished diameters. The fillets of the astragal then have their equal widths determined by several slight surface cuts, given with the chisel upon either side of the central piece to the left to form the round, alternated, by shavings removed from their cylindrical faces to determine their diameter; the obtuse corner of the chisel used in these two directions leaving well defined internal square corners, without being permitted to cut into either the cylindrical or the horizontal faces produced. The chisel if sufficiently narrow, is used upon the cylindrical faces lying almost flat upon the rest; but, when the blade is so wide that it would catch against the head on the one side or the band on the other, the tool is presented to the work supported on its edge, with the blade inclined vertically to right and left; when the cylindrical faces and internal corners of the fillets are produced with equal accuracy, and without risk of injury to the neighbouring portions. The bead of the astragal and the round edge of the head with its underlying fillet, are then completed with the chisel; the surface curve of the head being turned last, with the gouge travelling down hill, supported first upon its side, then gradually twisted to lie nearly upon its back and then again on to its side; when, the total length of the material being rather in excess of the finished length, as was originally permitted, the gouge leaves a little piece between the point of the work and that of the popit head.