In the ordinary saw-mill, the saws are stretched in a wooden frame, which slides up and down within another frame, in a similar manner to a window sash: the motion is given to it by a crank, attached to a fly-wheel upon the main axis, made to revolve by a water-wheel, or other power, and connected by gear that will give four or five revolutions of the crank to one of the water wheel. The timber is fastened upon a carriage, which is a horizontal frame, sliding or rolling between guides on the floor of the mill, and of such dimensions as to pass between the vertical frame, proceeding by a regulated motion, and constantly presenting the timber to the action of the saws. The saws are so fitted in the frame that they can be removed in a few minutes, and replaced by another set of sharpened saws.
Considerable improvements have been made upon saw-mills by Mr. Brunei, Mr. Maudslay, and many other engineers, who have, of late years, been engaged in their construction. The introduction of circular saws, which act by a continual rotary motion, formed an important era in sawing machinery, from the great facility, precision, and rapidity of its operation. A saw-mill of this kind has been employed for many years at the manufactory of the ingenious Mr. George Smart, near Westminster Bridge. In this, motion is imparted to a horizontal -haft, on which is a spur-wheel that turns a pinion on another horizontal shaft; on this second shaft, the bearings of the gudgeons of which are supported on the joists of the floor above, is a band-wheel, which communicates motion, by an endless strap, to a pulley fixed on the spindle of the circular saw, and causes the latter to revolve with great rapidity. The ends of the spindle are conically pointed, and the end nearest to the saw turns in a cavity made in the end of a screw, whose nut is fixed, and has a firm bearing in a stout bench; the other end turns in a similar screw, passed through a cross beam, mortised between two vertical beams, extending from the floor to the ceiling; one of the beams can be raised or lowered in its mortises by wedges put both above and below its tenons.
In order to adjust the plane of the saw to the plane of the bench, there is a long parallel ruler, which can be set at any distance from the saw, and fixed by means of screws going through circular grooves cut through the bench. In using the machine, the ruler is to be set the proper distance from the saw, according to 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 or ruler, that it may cut straight. The operation is, of course, very expeditious and accurate. Lathes are now frequently fitted up with circular saws.
Some improvements in mechanism of the latter kind were patented by Messrs. Sayner and Greenwood, in 1824, which we shall here describe. The first improvement mentioned in the specification relates to the adaptation of two circular saws operating together, instead of one, to cut through a piece of timber. By the usual process, it requires a circular saw of five feet in diameter, to cut through a log of two feet in diameter, in consequence of the obstruction of the axis and supporting shoulders; but by the application of two saws of little more than half the diameter of the single large saw, one above the log and the other under, each making an incision rather more than half way through, the division is effected with a considerable saving of power, and of the cost of saws. The annexed diagram is designed to explain the mechanical arrangement. a a is the bed of the saw-mill; b b the log of timber under operation; c c the two circular saws, the depths of their respective cuts being expressed by two right lines forming tangents to their peripheries; these saws have pulleys upon their axes, and are driven by endless bands embracing them and the drum-wheel d, to which motion is given by a water-wheel, or other adequate mechanical agency.
The timber rests and moves upon horizontal rollers e e, and is accurately guided to the saws by vertical rollers, not introduced into the figure, as they are common to other saw-mills. The axes of the saws run in fixed bearings, and the timber is forced against them by the revolution of the propelling roller g, put in motion by another band from the drum-wheel d, the axis of the roller being confined by an upright frame g h; in the upper part of which frame turns the pressing roller h, which being connected to the vertical bar i, is pressed upon by the weighted lever k; the rollerg therefore gives the motion, and the roller h a steady firmness to the advancing position of the log.
If the timber is to be cut into planks, a number of circular saws are placed together on the axes c c, with flanges between them of the thickness of the required planks, and then bolted together; by these means the whole log is at one operation formed into boards; and if it be required to cut the logs into scantlings or laths, a series of horizontal saws l, placed in like manner upon a vertical axis m, and driven by a pulley n, cuts the whole at once into those small divisions. This mode of applying the saws to work in a horizontal plane so as to operate simultaneously with those acting in a vertical direction, forms the second improvement claimed under the patent right.
A third improvement claimed, is for uniting the plates of a series of circular saws closely together, so as to make one compact body of saws, without any interstices between them, for the purpose of reducing dye-woods entirely to saw-dust or powder, instead of the usual method of chipping or rasping them for dyeing or other purposes.