Rectilinear sawing machines are for the most part derived from, saws used by hand for similar purposes; and under these circumstances it appears desirable that the machines to be noticed should, so far as practicable, be introduced in the order adopted in the last section; namely, machines derived from the felling, cross-cutting, and pit saws, and those from the frame, bow, and buhl saws.
Few sawing machines have been made for felling timber, because the labour of removing the machines from tree to tree, in general outweighs any mechanical advantage to be derived from their use. In the most simple machine of this kind, the saw is formed as the arc of a circle, attached to a wooden sector moving on its center, and worked with reciprocatiug motion by a horizontal lever.†
• As a mora expeditious mode of transferring the pattern than with the mallet, the three parts above described, have been squeezed in a flat screw press, this fails to bring up the impression, from the unequal thicknesses of the veneers; the hydrostatic press does not produce the required effect, and is liable to crush the wood from its enormous force; but the rolling press, such as that for copper-plate printing, was tried by Holtsapffel and Co., and found to succeed in all respects in transferring the pattern.
† Another construction for a felling and cross-cutting saw, which is more elaborate, is described in the Mechanics' Mag. vol. ii. p. 49-50; and at vol. iii. p. 1 of the same Journal, is a proposition for a pit-saw, which, as well as the above, it
In cross-cutting saw-machines erected in the Portsmouth Dockyard and Woolwich Arsenal, the timber is laid as through a doorway, the posts of which are double, so as to form two narrow grooves for the guidance of the saw; this resembles the ordinary cross-cut saw, except that it has two guide-boards riveted to it, in continuation of its length, and the boards work freely through the grooves in the posts. The saw is actuated by a vertical lever, or inverted pendulum, moved by the steam engine, and the workman bears down the opposite end of the saw with any required degree of force; the saw is guided in its first entry by a board with a saw-kerf, which then rests upon the timber, and when not in use the saw is turned up on its joint, leaving the doorway free for the reception of other timber.*
A cross-cutting saw machine of a more exact kind is erected at the City Saw Mills: the saw-blade is strained in a rectangular frame, which both reciprocates and descends in a vertical plane. The machine has a large double cross; the two horizontal arms have grooves that receive the rails of the saw frame, and which is reciprocated by a crank and connecting rod; the vertical arms of the cross fit in a groove formed by double vertical beams.
The cross and saw frame are almost counterpoised, so that a moderate psessure alone, and not their whole weight, falls on the saw teeth, and the timber is clamped on a railway or slide, which is at right angles to the plane of the saw's motion.
A cross-cutting saw machine worked by hand, that is much used on the Continent and in America, for cutting firewood, is represented in fig. 721. The wood is laid in an X form sawing horse, and fixed by a chain and wooden lever, which latter is brought under a peg. The frame saw is suspended by its lower angle in the deft of a lever that swings as a pendulum when the saw frame is moved. The lever supports and guides the saw frame, the action of which is assisted by the momentum of an adjustable weight, built out at right angles to the suspending lever. The saw always rests on the timber, and cuts both ways; and being guided in its required position, a person but little experienced in the use of the ordinary frame saw, can exert his whole strength in the act of cutting, and accomplish the work expeditiously, especially as the saw is longer than that shown on page 726, and employed in the ordinary manner for the same purpose.
Fig. 721, is proposed to work by means of the oft-repeated scheme, of a heavy pendulum put in motion by manual power.
* See Rees's Cyclopaedia, Art. Machinery for Manufacturing Ships' Blocks, Vol. xxii.; also Encycl. Metrop. Part Manufactures, Art, 532.
Upright or reciprocating saw machines, are largely employed to perform that kind of sawing which is usually done at the saw-pit; the larger upright or frame saws are used for cutting large round or square timber into thick planks and scantling, the smaller for cutting deals into boards. The earlier of these machines appear to have been those for round timber: they were mostly built of wood and driven by water power, these have been repeatedly described.*
The vertical saw mills now used in England are made almost entirely in iron, and driven by steam power, and as the several constructions differ but little either in respect to principle or general arrangement, the modern frame-saw for deals, fig. 722, will be principally spoken of. In this drawing the whole of the mechanism has been brought into view, by supposing the floor to have been removed, and some unimportant alterations to have been made; in reality the pedestals F F rest upon the floor, and the machine occupies considerable length.
* The reader interested in the practical details of the earlier saw-mills, is directed to Gregory's Mechanics, 1807, vol. ii., p. 324; and, in addition to the authorities there quoted, he will find useful matter on the subject in Hassenfratz's Traite de l'Art du Charpentier, Paris, 1804, in Evan's Young Millwright, and Miller's Guide, Philadelphia, 1821, and more particularly in the reprint of Belidor's work. Architecture Hydraulique, arec Notes, par if. Navier, Paris, 1819.
In Besson's Instrumentarum, published in 1578, at Plates 13 and 14, are two very curious and graphic drawings of saw-machines driven by manual power; the one by a crank and winch-handle; the other by a pendulum pulled as a church bell, and acting through the medium of a right and left-handed screw, and a system of diagonal links, as in the so-called "lazytongs." One of the saws has curvilinear teeth, of which 1, 3, 5, 7, cut during the descent, and 2, 4, 6, 8, during the ascent of the blade.