In operating with a common frame-saw, it would be ; at every successive cut, to sIsift all the transmits behind( the saw to the end o the or it would be necessary to take the saw out of the frame when a difficulty would arise of fixing • it again tightly. Both these objections are obviated by the plan we have described ; and by which, long deals, planks, and boards, may be cut with an important saving of materiel.
An expanding wear for the use of sawyer., represented in the subjoined sketch, was invented by Mr. T. Griffiths, el the Royal Institution, and was deemed worthy of an honorary medal from the Society of Arta. a is the handle or cen tre-Ore, to which is connected two springs e c, joined together at b ; the handle also carries a cross piece d. This instrument is intended to save the time and trouble of shifting the common wedges, while sawing up balks of fir into deals. When the saw ' has cut two or three feet, the loose ends of the springs c c are to be brought 17 band as near to the centre piece a as their elasticity will admit; the end b is then to be introduced into the cut, and the welts is to be thrust up to the end of the !ring, the cross piece d resting on e upper surface of the balk. The elasticity of thewill then be continually opening the cut as the Vs saw proceeds, to the of about twelve feet; and the wedge, when at its utmost expansion, will prevented, by the cross piece, from falling into pit.
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 fiy-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 :aim between guides on the floor of the mill, and of such dimensions as to pm between the vertical frame, proceeding by a regulated motion, and con shandy presenting the timber to the action of the saws. The saws ate so fitted in the frame that they can be removed in a few minutes, and replaced by anGtber set of sharpened saws.
Coneiderable improvements have been made upon sawmills by Mr. Brtmel, Mr. Maudslay, and many other engineers, who have, of late years, beep engaged in thew construction. The introduction of circular saws, which act by a continual rotary motion, formed an important era in sawing machinery, from the great facility, and rapidity of its operation. A. sawmillsawmillof 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 shaft, on which is a spur wheel that turns a pinion on another hori zontal shaft ; on this second shaft, the bearings of the of which are supported on the joists of the floor above, is a band-w w 'ch 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 beam', 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 tote met the proper distance Sons the saw, according to the piece of wood to be cut; and as the saw turns round, a work-. man elides the end of a piece o. wood to it, keeping its edge against the guide sr ruler, that it may tut straight. The operation is, of course, very expecil- • tious 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. is the bed of the sawmill; bb the log of timber under operation ; e 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 intro duced into the figure, u 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 revo lution 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 ; in the upper part of which frame turns the pressing roller A, which being connected to the vertical bar i, is pressed upon by the weighted lever k; the roller g there fore gives the motion, and the roller A a steady firmness to the advancing posi tion of the log.