and — Figure 3 is a combination of saw- and flour-mill operated by animal-power, and of interest to those who follow the history either of sawing or of mealing processes. As will be seen, it may be arranged so as to be used both for sawing lumber and for grinding cereals. The upright beam A with its horizontal cog-wheel is driven around by the animal (as shown in the cut); a cog wheel connects with the spindle of the trillis B, and by that means drives the other upright beam H, to whose lower end is attached a double cog wheel (C); the upper cogs move in the trillis D (on the right) and the side cogs in the trillis F(on the left), the latter operating the millstone G and the former operating the wheel E, which by its connections at L ope rates the saw ill below, thus giving actually two mills operated by one means of power. At the upper end of the beam B is placed the large wheel I, to which three (not four) heavy weights (K) are suspended; this is clone both to obtain increased power and to relieve the strain on the animal.
4 represents a primitive saw-mill used for cutting large trees into planks or boards; it is driven by water-power, and can he erected and operated on the banks of a stream. The wheel Z is the main motive power; to this is attached a curved arm (X) which is fastened to a horizontal bar (T), with uprights running through the grooved or slide-frame S, S, having on the top thereof a cross-bar, to which the saw is attached. The wood IV to be cut is fastened with wedges on an elevated platform between the beams ,VA and the up-and down motion of the arm X produces the sawing.
considered with reference both to their blades and to the machines that drive them, may be divided mainly into two classes: (t) reciprocating and (2) continuous-acting. In the first division the saws that act alternately or with a reciprocating motion have straight, or nearly straight, blades. Saws with straight blades may be subdivided into those held at one end only and those held at both ends, the former includ ing those that cut upon the pull-stroke only, those that cut upon the push stroke only, and those that cut upon both. There are three varieties of coutinuous-acting saws—namely, (r) band or ribbon, (2) circular or disc, and (3) cylindrical or tubular. With these may be included spiral and chain saws, which are in some measure varieties of the band, and the spherical-segment or dished-circular saw, a variety of the circular proper or flat disc. Cylindrical or tubular saws are of two kinds; one of these acts at right angles to the plane of the material to be cut, as in the case of the trephine or trepanning-saw used in surgery to cut a disc out of a skull, while the other, the barrel-stave saw, acts with its axis parallel to the length of the piece to be cut, and produces a stave-like piece with one side concave and the other side convex. The spiral saw, used principally for dovetailing, is a cross between the band- and the circular saw. A large part of its work is widening with one portion of its cutting-edge the kerf made by that part which precedes it. Circular saws may be divided into those set with their discs or planes at true right angles to their axes or arbors and those having a slight inclination, which causes them to " wob ble " in running.
Saws may also be classified into those used singly and those employed in gangs. Both straight and circular saws are used in gangs having sev eral sets of parallel cutting-edges, and furthermore circular saws are also so mounted that instead of having several saws upon one axis there are two or more on different axes. Two band-saws may also be arranged to make parallel cuts.
some saws the teeth are cut out of the solid blade or disc, whose effective diameter becomes diminished as the teeth wear down, while in others the teeth are inserted (pi. TO, fig. 6), and when they are dulled or damaged may be removed and others substituted. Between inserted- and solid-teeth saws there is a middle variety with removable segments (fig. 7), each bearing several teeth, so that any one segment, if damaged, may be removed and another substituted; and when all the segments are worn out, they may be exchanged for a new set, leaving the effective cutting diameter the same as it was originally. Moreover, one centre may have several sets of segments, by means of which the saw may be given any one of several effective diameters.
Aside from the use of saws for cutting stock in two or more pieces, a very important application is for " crozing" or "gaining" (cutting grooves), particularly in barrel-, vat-, and tank-work.
SaWS. —Sawing-machines employing straight blades may be divided into " strained " and "unstrained," the former being held at both ends and the latter at one end only. Of those with unstrained blades the "drag" and the " =lay" cut upon the pull-stroke only, and need no guide, because the greater the resistance, the more taut the blade is pulled.
The Drag-saw, which differs from the mulay in being horizontal, while the latter is vertical, answers well for cross-cutting logs and for cutting staves, heading- and shingling-bolts. As its tip is not guided in a straight line, but is free to describe an arc, the blade is generally a practical pro longation of a crank-driven pitman. In the ordinary cross-cut saw the feed is effected by gravity only, the blade commencing at the top of the log and gradually working through. In one form (t1. Tr, fig-. i) the crank-disc is arranged between the log and the pitman cross-head, thus giving a very long reach to the rod bearing the saw. In one of the most convenient drag-saw machines the blade may be drawn up out of the way when through, ready to be lowered for another cut; and, as the crank-pin is attached to the disc, and is also adjustable, the "throw" may be varied. The drag is used principally for cross-cutting logs, and one variety, fixed to the cross-head of a small steam-engine, is made in Europe for felling trees by sawing them through close to the ground to, fig. 8), the blade lying flat and the feed being effected by a special mechanism which gradually swerves the entire machine in a circular arc. It may also be arranged for ordinary log cross-cutting.