The saw is composed, first, of a cast-iron wheel or chuck, with from six to eighteen arms, which are taper, so as to constitute a cone, the thickness of which at the center is about one-twelfth the diameter. The rim of the wheel c c, is flat and turned smooth on the face to receive a series of 6 to 18 segments of soft steel, about one-quarter of an inch thick, marked s s, which are fixed to the cast-iron by strong rivets; the segments project from 5 to 8 inches beyond the cast-iron, and are chamfered at the edge. To the soft-steel segments s s, are affixed a second series h h, consisting of about twice the number; these are hardened and serrated, so as to constitute the cutting edge of the saw.
The tempered plates are technically called the hard, and are attached to the soft segments by numerous countersunk copper screws, tapped into s s. When bow, the hard segments project from 4 to 6 inches beyond the soft; so that the angle then formed by the three parts, h to c, considered collectively, is only about 4 to 6 degrees with the flat face of the saw, and the veneer will readily field to more than that extent from the log without splitting. To prevent the risk of accident from the exposed spokes of the wheel or chuck, and also the current of wind caused by their rapid rotation, the spaces intervening between them are filled up on the face with wood, and an entire cone of thin boards is attached to the hack of the chuck.
The log to be sawn sometimes requires to he previously adzed all over, to remove the sand and dirt that would soon blunt the saw; it is then partially levelled with the adze or plane, to adapt it to the vertical face of the drag. The drag has three long ban of wood, in order that the revolving saw may cut or prepare for itself the surface against which the log is fixed. The sharp ends of the iron dogs are driven a little way into the log, and the dogs arc then drawn down by screw-bolts as represented.
Sometimes the log is only temporarily held by the iron fastenings or dogs, whilst its surface is partially levelled with the saw, after which it is glued on a wooden frame, that is full of transverse and oblique bars, and has been also levelled with the saw; the log and frame are afterwards bolted to the drag. In this case the entire body of the wood can be cut into veneer without inter-ruption from the fastenings, and the glue joint is safe so long as the log does not project more than the width of the glued surface.
The timber requires two motions to be impressed upon it; the one motion, longitudinal, to carry it across the face of the saw; the other motion, lateral, to advance it sideways between each cut, the exact thickness of the intended veneer.
For the first or cutting motion, a long railway extends across the face of the saw, and supports the drag, which is carried past the saw by means of a rack and pinion, actuated by a cord proceeding from one of the grooves of the cone pulley on the mandrel, down to the pinion axis, which is beneath the surface of the ground, and not represented. On the pinion axis there is a double train of toothed-wheels, and a clutch-box, by the three positions of which latter, the drag is left at rest, or it is carried slowly past the saw in the act of cutting, or quickly back preparatory to the succeeding cut. The gearing lever, by which the three positions of the clutch-box are given, is perpendicular, and passes downwards through a trap-door, situated close behind the little stool on which the attendant is seated.
The second motion of the log, or its lateral adjustment, is thus effected. The slide that runs on the railway has a horizontal plate, which carries three or more triangular standards, like buttresses, to the perpendicular faces of which are fixed the three wooden bars against which the wood is clamped.
The horizontal plate that carries the triangles, is united at each end to the lower piece of the drag, by a chamfer slide with an adjusting screw and nut, one of each alone being seen. The adjusting screws have worm-wheels at the one end, and are simultaneously moved by means of a winch-handle w, at the extremity of a long rod, having two worms taking into the two worm-wheels fixed on the adjusting screws. From 50 to 60 turns of the handle are required to advance the log of wood one inch; the attendant can therefore determine with great facility, the number of veneers cut out of each inch of wood, or he can cut the veneers to any particular pattern for thickness.
There is no impediment to the passage of the log across the rectilinear face of the saw; but for the guidance of the veneer around the back of the cone, some particular arrangements are required. To enable the veneer to avoid the edge of the soft steel segments, to which the serrated blades are fixed, a feather-edged guide-plate, usually of brass, and extending around about one-sixth or eighth of the circle, is fixed almost in contact with the blade, by screw-bolts and nuts, which, as seen in fig. 804, unite it to the stationary framing of the machine; the guide is represented black in the sectional view, fig. 803. As the veneer it sawn off, the attendant leads the veneer on to the guide, by means of a spud, or a thin blunt chisel, the veneer then slides over the guide, as shown, and proceeds through a curvilinear wooden trough, usually extending round the back of the cone, and the veneer is pulled out on the other side by an assistant, and stacked on the heap. Sometimes the veneer is bent nearly at right angles, and quits the saw in front, as in the figure: this arrangement is less usual, but was selected for the illustration, as it offers a more comprehensive view of the several parts.
Before running back the drag, preparatory to a new cut, the handle w, is unwound two or three turns, to remove the log beyond the reach of the saw, and prevent its being scratched by the saw teeth, these turns are afterwards moved in addition to those required for the new thickness: the handle is managed by a boy, who stands outside the railway.