The teeth of carpenters' saws are so formed as to contain an angle of 60', and they are made to incline more or less forward accordiug to the intended use of the saw. Ripping-saws have the front of the teeth perpendicular to a line ranging with their pointa. For very delicate operations saws arc frequently made of watch-spring.
Saws for cutting atone are without teeth, although they are some times slightly notched upon the cutting edge. The saw-plate is tightly stretched on a kind of rectangular frame, of which it forms the lower aide ; and the frame, being suspended by ropes, is moved backwards and forwards by one or two men. Coarse sharp sand is used for cutting soft atones, and fine sand for those of harder quality. Sawing stone is a very slow and laborious operation. As in sawmills for wood, any number of saws may be worked together, so adjusted as to cut a block of steno into slabs of any required thickness.
Saw Nal.—The machinery used for the purpose of converting wood from the log into squared lumber, or for subsequently cutting it up into plank, or veneer stuff, is known in the arts under the generic name of saw milt. It consists of a prime mover, setting in operation either a circular plate with serrated edges, vertical saw blades fixed rigidly in a frame, or a series of knife blades forming the segments of a large circular plate bearing a sharp cutting edge ; and at the same time motion is communicated by the prime mover to a ratchet-wheel, which causes the frame to advance horizontally so as to keep the log of wood to be operated upon in actual contact with the edge of the cutting-tool. Rough logs and scantling stuff are cut by the circular saw ; and deals, battens, and planks are dressed for the market by the same description of machinery. Thin boards (between 14 inch and of an inch in thick ness) are cut by the frame saw ; and veneers, or thin slices of the harder and more precious woods, are cut by the plate saws with knife edges. As many as 100 veneers are at times cut out of planks only 1 inch in thickness.
The prime motors of saw mills may be either water-wheels, wind mills, or steam-engines, and even in some cases horse-power is used.
In mountainous districts, such as are usually covered *ith forests, water-wheels can generally be economically established, and they are rarely used for any other purpose than for squaring logs, or dressing plank stuff. Windmills are largely used in such countries as the Fens of East Anglia, and Holland, for both circular saws and frame saws; whilst the application of steam power to this purpose is the system almost universally adopted, in countries where fuel in cheap, for the ordinary kind of saw mills, and it is tho only motive power ever employed for veneer cutting. Of late years, circular saws have been
used for the purpose of cutting the ends of iron rails, and they also are Invariably worked by steam power. The sizes of circular saws vary from 4i to 60 inches in diameter ; vertical saws are made of cast steel of Noe. 13, 14, and 15 gauge, and from 4 to 8 inches wide by from 3 to 7 feet in length ; veneering saws vary from 4 to 10 or 12 feet in diameter.
All the varieties of apparatus that have been described are for the purpose of making straight cuts ; but it is sometimes desirable to pro duce curved forms by sawing, for which purpose there are several ingenious contrivances. Mr. Trotter has invented a concave circular saw, resembling a watch-glass in form, which is mounted in a bench like the common bench-saw, and to which the wood is directed by curved guides. Many useful forms are cut by a saw consisting of a.
cylinder of steel, toothed on the edge. Such saws are used for cutting circular pieces of wood to form the sheaves of blocks; and, when of larger dimensions, for cutting chair-backs, felloes of wheels, curved brush-handles, &c. For these purposes they are sometimes used as much as five feet in diameter. In another machine, an arrangement resembling the common reciprocating saw-mill is applied to curvilinear sawing, by causing the carriage on which the timber is supported to deviate from the straight course, and follow the curvatures of a model of the required form; while the saws, being attached to the frame by pivots, are capable of adapting their position to the curve.
Among the recent inventions in saw-machinery is a beautiful appa ratus called the band-saw. It consists of a very long, narrow, and thin saw, made of highly tempered steel, and so flexible as to be wound round two rollers placed at such a distance apart as to keep. the saw always on the Stretch. When the rollers rotate, the saw is put in motion, and it thus becomes an endless saw, applicable to many. purposes in the finer kinds of carpentry and joinery. Messrs. Poing. and James's band-saw, patented in 185S, is an elegant example of this kind.