Sawing machines for round timber, arc larger, stronger and somewhat different from the deal frames. The timber-slide moves on fillets or V. V.'s, which are fixed to the floor, and passes between the standards of the saw frame; the timber slide has strong vertical end plates, through mortises in which stout iron spikes or dogs are driven like nails, into the ends of the required planks. The dogs arc then secured by side screws or wedges in the dog plates, from which they project sufficiently, to allow the saw blades to stand between the end of the timber and the dog plate, at the commencement of the sawing.
The sliding frames carrying the saws for timber frames arc longer than for deal frames, and those in the Government saw mills at Woolwich rest in contact with rectangular fillets on the standards, against which they arc pressed by powerful springs, so that the square bars b b, fig. 723, are dispensed with. In these machines the blades are strained one at a time by a loaded lever, like a Roman steelyard, which gives to each the tension of about one ton, and whilst under this tension, the wedges are driven just home, but without violence; each blade becomes therefore tense alike. Various contrivances are added to vertical saw machines driven by power, so that, when the saws have arrived at the cud of the timber, the motion of the wood or that of the entire machine may be arrested automatically.
Rectilinear sawing machines arc not much used for those kinds of work that arc performed with the ordinary hand saws, back saws, and frame saws, used in carpentry; but two useful scies mecaniques suited to works of this scale are described in the Manuel du Tourneur, and fig. 724 is reduced from one of these.
The saw frame has a central wooden rod, and a blade on each edge, which are stretched by clamps, screws and nuts, much as usual. The saw is guided perpendicularly by fixed wires; these pass through holes in the cross heads of the saw frame, which are sometimes fitted with rollers to relieve the friction. The saw frame is suspended from a bow spring attached to the column erected on the bench; and the lower end communicates by a double-ended hook with a light treadle. The spring, when left to itself, raises the saw frame and treadle some 8 or 10 inches, and the pressure of the foot gives the cutting motion.
For straight pieces a wide saw is used, and the work is guided against a square fence, which overlaps the front edge of the bench, and is fixed by a binding screw passing through a mortise. For bevilled pieces a chamfered bar c, is fixed to the right hand side of the bench, and carries a square sliding block, surmounted by an angular fence, with graduations and a clamping screw; the work is laid against the angular fence, and moved upon the chamfer slide past the saw. For circular works a narrow blade is employed, and the popit head or center point connected with the stationary frame work, serves as the axis of motion for the piece of wood to be cut.
In order to leave the bench unobstructed, so that large pieces may be sawn, the guide rods upon which the saw frame works are discontinuous; the lower parts terminate beneath the bench, the upper are fixed to cross pieces, connected with a dovetail bar, itself attached in front of the column, so that the group of pieces carrying the upper wires may be fixed at a greater elevation to macduff's buhl saw machine.
admit of thicker work. The back edges of the blades run in saw-kerfs in the lower rail of the guide frame.*
Three small reciprocating saw machines, fitted up as adjuncts to the lathe, will now be described; their constructions are entirely different, and they were planned by their reaper inventors quite independently of each other. The one first described was especially contrived for buhl cutting; this appears however, to be far the least valuable application of these machines, as they may be much more efficiently used for various works similar to those done by the slender bow or sweep saw. The extreme delicacy of buhl work, is incompatible alike with the encumbrance arising from the mechanism, and the friction of tin-work upon the supporting platform.
In Mr. Mac Duffs buhl cutting machine, the saw is stretched in a frame about 4 to 6 inches high and 10 to 14 inches wide; the frame reciprocates vertically upon small fixed wires, by the modification of the crank shown in fig. 725. The pulley e, beneath the lathe bearers b, receives continuous motion from the foot-wheel, the lower end of a cord c, is fixed to a pin about an inch from the center of e, passed around the fixed pulley p, then between the bearers to the saw frame, which is raised by a spiral spring; by this arrangement, the parallelism of the cord is obtained. The work is supported upon a table or platform, midway between the path of the saw frame.†
* A machine on a somewhat larger scale was erected by Mr. Brunei, at the Woolwich dockyard, and worked by the peculiar but expensive parallel movement of the interior epicycloid. There is a, fixed wheel, say of 16 inches diameter, with internal teeth, and a corresponding pinion of 8 inches diameter, carried round by, and revolving upon the end of a crank of 4 inches radius; the pinion carries a stud by which it is connected with the saw frame. The velocities of the crank and pinion are as 2 to 1, and in the tame direction; the stud, if attached to the center of the pinion, would move in a circle of 8 inches, but when attached to the edge or pitch line of the pinion, it reciprocates in a right line, 16 inches long; the stud, if placed in any intermediate position, would travel in an ellipsis.
A reciprocating saw machine for sawing, boring, and manufacturing bevilled and curvilinear works in wood, was patented in 1838, by Mr. Samuel Hamilton, and is briefly noticed in the foot note following the application of the circular saw to curvilinear works.