In the saw invented by Lieutenant J. W. Hood, for cutting through ice, the blade is suspended from the end of a lover, like that of an ordinary hand-pump, and has a heavy weight beneath the ice. The axis of the lever is in a wooden frame, or sledge, the progression of which is caused by the end of a rod or paul-that sticks into the ice; the rod being jointed to the lever a little in advance of its pivots, thrusts the frame and saw some three or four inches forward during the act of cutting. This ice-saw is worked by two to four men, whereas the previous methods used in the Greenland fisheries, with a triangle and pulley blocks, required from twenty to thirty men. - Trans. Soc of Arts, 1827, vol xlv., p. 96.

The stationary frame work in fig. 722 consists of two standards or vertical beams, in front of which are fixed two accurate square bars, by means of six loops. The sliding saw frame shown geometrically in fig. 723, has four vertical and two horizontal bars and is cast in one piece, or as a rectangular frame, which is attached to the stationary square bars b b, by appropriate bearings at the four angles. One central crank is in general used, but for greater distinctness, the drawing is made from a machine having two exterior cranks, although one only is represent the crank rods arc not attached directly to the saw-frame, hut to a floating lever, which is jointed at its center to the saw-frame; so that even supposing the two cranks to be a little dissimilar in length or angular position, they nevertheless move the platform equally, without straining or racking it.

Rectilinear Or Reciprocating Saw Machines Part 2 200176

When only one crank placed beneath the floor is employed, it is needful, both to avoid excessive height in the machine, and the disadvantage attending the action of a short connecting rod, that the latter should pass freely through an oval loop in the lower cross rail of the saw-frame, and be united to the upper rail; sometimes the crank shaft is fixed to the ceiling of the building, but this construction is the least in estimation. The crank shaft, in addition to the driving pulley, has always a heavy fly-wheel to equalise the action of the machine, but which is not shown in the drawing.

Two deals are usually sawn at once; the parts now to be described are therefore in duplicate, although in the figure, one deal is supposed to be removed for the purpose of showing the mechanism more distinctly. Generally each deal has to be cut into three boards, and two saws are then employed on each side of the frame; but sometimes as many as eleven thin saws or v are used, then producing twelve thin boards or leaves from each deal. The saws, of which one is shown at s s, have buckles riveted to them, and these pass through mortises in the top and bottom rails of the sliding frame; the buckles at the bottom are solid and shaped like an inverted T, those at the top have mortises and thin steel wedges; the T pieces and wedges bear on the outsides of the frame.

The distances between the blades are adjusted by interposing pieces of wood, and pressing the whole together by the side screws, after which the saws are separately tightened by the steel wedges: these details are sufficiently manifest in the geometrical view, fig. 723. It is to be further observed that the edges of the saws are not quite perpendicular, but haw a little lead, or thru-upper ends overhang the lower about 1/4 or 3/8 inch, to extend the cut throughout the descent of the blade, and to carry the saws a little distance from the cuts, in the ascending or back stroke.

The two deals lie on a series of rollers built on pedestals, of which two only are shown at F F; the rollers also support a long rack, which, at the left of the figure, has dogs or nippers, that grasp the end of the deal by means of a side screw. The weight to the left of the figure, pulls the longer end of a horizontal lever, the shorter end of which (not seen), has a roller that presses the part of the deal contiguous to the saw, against a fixed vertical plate or fence, so that the cuts become exactly parallel with the side of the deal, whether it be straight or crooked.

The deal is advanced by means of the rack and pinion, which are actuated by a ratchet movement as follows: an eccentric on the main shaft alternates the shorter end of the lever l, and to the longer end of the same is fixed the ratchet or paul, which according to its distance from the center, slips over two or three teeth in its descent, and in rising thrusts the ratchet-wheel round the same distance, and by its connexion with the pinion for the rack, advances the rack and wood a proportionate quantity. The retaining pauls or detents on the top of the wheel prevent its retrogression; when they are turned back, the wood ceases to advance, and the slide may be run quickly back by a winch.

The plank frame by the late Mr. Benjamin Hick, of Bolton, (of which a model is deposited in the Museum of the Inst. Civil Engineers) has no long rack. Each deal is grasped between two grooved feeding rollers; the one fixed to the framing of the machine, the other pressed up by a loaded lever, and moved a small step at a time, by a ratchet as usual.

The single saw frames above described make about 100 to 120 strokes, of 18 or 20 inches long, in the minute, and cut two 12-foot deals in from five to ten minutes; the saws require to be sharpened about every tenth round, or journey, for hard deals, and every twentieth for pine. Similar frame saws are made double, so as to operate on four deals at a time; the crank is then double, and so contrived that the saws in one frame descend, whilst those of the other ascend. By this arrangement the vibrations of the machine are somewhat lessened, so that the velocity may be increased to about 160 or 200 strokes in the minute; but the time occupied in fixing and adjusting is also greater, so that but little if any real advantage is obtained.