SAWING, dividing timber, &c. by the application of a saw, either by the hand or mill. The mechanism of a sawing-mill maybe reduced to three principal things ; the first, that the saw be drawn up and down as long as is necessary, by a motion communicated by water to the wheel : the second, that the piece of timber to be cut into boards be advanced by an uniform motion to receive the strokes of the saw ; for here the wood is to meet the saw, and not the saw to follow the wood, therefore the motion of the wood and that of the saw ought immediately to depend the one on the other; the third, that when the saw has cut through the whole length of the piece, the machine stops of itself; and remains immoveable, for fear, lest, having no obstacle to surmuont, the force of the water, or steam, should turn the wheel with too great rapidity, and break some part of the machine.
In Plate Saw-mill are drawings of a cir cular saw-mill, used by Mr. George Smart, at his manufactory for hollow made masts, Westminster Bridge. Fig. 1, is an elevation of the machine ; fig. 2, a plan ; and fig. 3 and 4, the saw shown separately.
The machine is turned by a horse wheel, which gives motion to a pinion on a horizontal shaft; a spur-wheel is fix ed on this shaft, and turns a pinion on another horizontal shaft, on which the wheel A, (fig. 1.) is fixed ; this wheel is in the room over the machine, and the bearings for the gudgeons of the shaft are supported on the joists, B, of the floor : by means of an endless strap pass ing round this wheel, and also round a pulley N, on the spindle of the circular saw, a rapid motion is given to the saw, which is made of well tempered steel plate, (fig. 3.) with teeth on its edge : it is fixed on its spindle, D, (fig. 4.) by a shoul der, d, against which it is held by another moveable shoulder, e, pressed against the other by a nut, k, on the end of the spin dle, which is tapped into a screw to re ceive it. The saw has a circular hole through the middle, fitting tight upon the spindle, and a small fillet fitting into the notch, a, (fig. 3.) causes them to turn to
gether.
The ends of the spindle are pointed, and that point nearest the saw works in a hole made in the end of a screw screwed in a bench, F. F G H, (fig. 1. and 2.) made of stout planks, and well braced together the other turns in a similar screw screw ed through a cross beam, K, mortised be tween two vertical beams, L L, extending from the floor to the ceiling : the cross beam, K, can be raised or lowered in its mortises through the beams L, by wedg es put both above and below its tenons. In order to adjust the plane of the saw perpendicular to the plane of the bench, M M, is a long parallel ruler, which can be set at any distance from the saw, and fixed by screws going through circular grooves, gg, cut through the bench. In using the machine, the ruler, M M, is to be set the proper distance from the saw of the piece of wood to be cut, and as the saw turns round, a workman slides the end of a piece of wood to it, keeping its edge against the guide, M M, that it may cut straight.
When the saw requires sharpening, one of the screws at the end of its spindle must be turned back : the spindle and saw can be then removed; and by taking off the nut, ir, the saw will be loose, and may be fixed in a common vice to whet it, in the same manner as a common saw : the teeth of the saw are set, that is, bent out of the plane of the saw, one tooth on one side, the next on the other : the out sides, r, (in fig. 3.) of the teeth are not filed to leave a surface perpendicular to the plane of the saw, but inclined to it, and in the same direction that each tooth so filed is bent in the setting: by this means the saw, when cutting, first takes away the wood at the twosides of the kerf, leaving an angular ridge in the middle of it, the use of which is to keep the saw steady in a right line, that it may not have so much tendency to get out of the straight in any place where the wood is harder at one side than on the other.