† Mac Duff's buhl saw received the prise of 10/. awarded by Dr. Fellowes: and is fully described in the Mech. Mag, 1880, vol ziii. p. 129; at page 285 of the same volume Mr. Mae Duff has described a larger and more simple machine of the same kind.
hind's vertical saw machine.
In the two following machines the saw is unprovided with the frame, by which, under ordinary circumstances, it is stretched and guided, these functions being fulfilled by the motive parts of the respective apparatus.
Mr. Lund's vertical saw machine, which is represented from the back in fig. 726, consists of a bench with foot wheel and treadle, surmounted by a rectangular frame, the lower rail of which is rebated to fit the bearers; the center rail is extended into a platform about three feet square, which, for the sake of portability, consists of two wide flaps with hinges and brackets, somewhat as in an ordinary pembroke table. To the extremities of the upper rail are fixed two long and narrow springs, made of hammered steel, that spring downwards when left to themselves. The ends of the saw are grasped in screw clamps, formed at the ends of square wires, working rather freely in the two outer rails, within holes fitted with metal. The lower saw clamp is connected by a cat-gut with an eccentric and guide pulley, as in Mac Duff's, but the eccentric shown detached in fig. 727 has more range, the traverse being sometimes 4 or 5 inches.
The upper saw clamp is connected with the straight springs by means of a catgut line, reeved in the manner shown more at large in fig. 728 (one of the side frames being removed), the catgut proceeds from the springs, over the two fixed pulleys, and under the pulley on the top wire or clamp; this arrangement equalises the actions of the springs, and gives a parallel motion to the blade, the back edge of which lies towards the operator, and works in a notch on the edge of a hardened steel disk, inlaid in the platform. One end of the catgut has a small circular button, which is passed through a round hole in the spring, and then sideways into a notch, so as to be readily detached for the removal of the saw.
Mr. Lund's machine is simple and effective for inlaid and fret works, and a variety of thin curvilinear pieces, which occur in cabinet work and pattern making. For cutting parallel and bevilled pieces, appropriate guides are added to the platform, similar to those elsewhere described. For circles, a brad-awl is passed through the center of the work into the platform, or rather into a subsidiary and common platform then added. And to shorten the length of stroke during the working of the machine as required in sawing around small curves and rounded angles, a sliding bolt beneath the platform, is thrust across the path of the saw, so that the ascent of the saw to the full height is then prevented by the temporary increase of thickness in the platform, as the saw clamp strikes against the sliding-bolt or slide.*
Fig. 729 is copied from Professor Willis's sketch of a vertical saw for curvilinear works, constructed by himself in 1837. The frame of the machine is elevated above its true position to show the details, and is clamped on the bed of a lathe or grinding frame, and the saw derives its motion from an eccentric carried by one of the ordinary grindstone spindles. This eccentric is a pulley of hardwood cut in half and screwed against the face of the mahogany pulley. A loop of wire embraces it, and connects it with the lower spring, so that when the spindle revolves the spring is thrown into rapid vibration; the springs are of wood, 21 inches long and 2 1/2 inches broad.
* Mr. Land makes an ingenious use of this machine for inlaying the instruments in dressing-eases lined with velvet. The bottom of the trays are glued up in three thicknesses, the grain of the inner piece being crossways, of the outer lengthways, a piece of white paper is added to receive the outlines of the instruments, the spaces for which are then cut in the saw machine, with a saw thinned away at the back, and very much set to cut a wide path.
The inner pieces having been removed, are split through the joint and glued flat down on a piece of velvet; each inner piece is then cut round with a penknife, leaving the face alone covered. The principal piece, or skeleton, is then glued and laid on another piece of velvet, which covers the holes as in a drum; the velvet is cut through at various parts of each aperture, and folded round the edges of the holes, and lastly, every removed and covered inner piece, is pushed into its place, which stretches and smooths the edges of the velvet, and completes the work. As the central pieces are in three layers, the cells may be either of one-third or two-thirds the entire depth, at pleasure.
Mr. Lund's saw machine was constructed and used in 1828.
The saw is clamped at each end in a small iron clamp; the lower clamp is joined to the lower spring by the same steel pin that carries the loop of wire. The upper clamp has several hooks filed in its edge, any one of which can be hooked on a steel pin fixed to the upper spring. Thus the saw is carried and stretched at the same time by the two springs, and can be readily disengaged, either by unhooking the upper clamp or by unclamping either end. The lower spring is fixed to the frame, the upper is fixed to a separate piece of wood that can be adjusted to different heights, and the platform is 12 inches above the bearers.
The only point that requires further consideration is the adjustment of the saw in the springs, so that it may traverse as nearly as possible through one and the same point of the platform, notwithstanding that the ends of the springs nearly describe arcs of circles, and therefore carry the extremities of the saw slightly to and fro during its movements.
The vertical distances between the springs at their roots, where they are fixed to the framing, and at their pins where they carry the saw, must be so adjusted, that when the saw is at the top of its stroke, the lower spring is horizontal; and when at the bottom of its stroke the upper spring must be horizontal, and the platform midway between the two horizontal lines. In this condition, with a range of two or even three inches, the one curvature will neutralise the other at the platform, as in some of the parallel motions, which may be proved by a diagram carefully drawn on paper.
Professor Willis has used this machine extensively for cutting out in thin wood, models of Gothic tracery, also mathematical curves in illustration of the teeth of wheels and other elements of mechanism. To adapt the machine to take cither short or long strokes as required in buhl cutting, without discontinuing the motion of the foot-wheel, Prof. Willis proposes to apply a contrivance to the eccentric, analogous to that explained in his Treatise on the Principles of Mechanism, p. 445.
A very curious sawing machine, the connecting link between rectilinear and circular saws, was patented by Mr. Newbury in 1808, and is thus described. - "Nr. Newbury's engine is formed by a long and very flexible blade of a similar nature to a clock-spring, which passes over two rollers of considerable diameter, placed in the same plane, and whose extremities are united soas to form a band round the two rollers. When this blade is intended to act as a saw, one of its edges is cut into teeth of the usual shape, and the substance to be sawed is placed on a stage, through which the blade passes, and is pressed against the blade Willi the necessary force, and in the direction proper to produce the shape required for it."* Guides for cutting rectilinear, curvilinear, and circular pieces are alluded to, the description does not however state the most difficult point of the construction, namely, the mode adopted in joining the ends of this clastic Made, or ribbon saw.