(Continued from page 179.) No tool is used in a greater variety of in dustrial occupations than the saw, and when made in a circular form it is even more useful than when rectilineal, finding alike a place among the minute tools of the optician and among the rough but rapid working instru. ments of the backwoods. In employing the circular saw to cut lumber, the primary sub. ject of inquiry is concerniffg'its diameter,as a rule it is generally advisable to employ a saw of as small a diameter as circumstances will permit, for the resistance, the surface friction, and likewise the waste from the thickness ot the plate, rapidly increase accor ding to the size. But if the saw is so small as to be nearly buried in the work, the metal be comes heated, the escape ot the dust is pre vented, and the rapidity of the sawing is con sequently rH minished. As a general rule it appears best to use that part of the saw which is nearest to the centre, and to allow its diameter to be about four times the average depth of the log. Circular saws are usually fixed on mandrels, which revolve in bearings securely united to the stationary frame-work of the saw bench, the end play of the spindle being pl'evented by collars, as it is highly important to check any lateral motion. The saw is placed hetween two plates or flanges, which are firmly pressed against the former hy a nut, so that they compel ib to accompany their reo volutions as the mandrel revolves, and to fur. ther ensure the saw's rotation, steady pins are passed both through the saw and the fixed flange. When the diameter of the saw is con siderable, compared with that of the flanges, the blade is very flexible and liable to be di. verted from the true plane. In order to pre vent this, there are many diffe:ent contrivan. ces; when a wooden bench is employed, the saw works in a narrow groove, which it cutsti for itself in the bench, or a metal plate with a suitable slot is sometimes used, but a preferable method is to inlay a piece of hard wood and allow the saw to form the groove. Other methods, namely, to guide the periphery the saw by rollers, or to employ two smal saws in lieu of a larger one, are devices fami. liar to our readers. Sawing apparatus of both these and of nearly every other description, will be found illustrated and explained inthe back and current volumes ot the " Scientific American." When it is designed to use this tool for cutting wood at any angle, it is cus tomary to make the platform adjustable, am that to an extent commensurate with the exi. gency of the case; a more simple way is t use supplementary wooden beds placed to th angles required. A plan for cutting weather 3k. boards out of a sound log, has been proposed, when the timber is placed between centres over the revolving saw, which makes a ver tical and radial incision, the tool is then releas-ed and the wood shifted on its axis for a new cut, so that the entire tree is sawn into feath. er.edged boards. In this insta!lce the saw is novel in design, on account of its being buried so deeply in the wood, a circular plate is fitted with four pieces ot steel, each having two teeth, while a great velocity atones for the paucity of these latter. The cutting of veneers is undoubtedly the most remarkable instance of the precision that can be attained in the operation of sawing j for this description ot work the saw is gene rally large, and here advantage is taken of the pliancy' of the veneer, which allows the saw to be thick towarus the centre, whilst" it is thinned away towards the edges. In the large application of the principle, the saw is compo sed of many segments, and is often 18 feet in diameter. For sawing ivory in thin leaves, the saw is a single plate from 6 to 36 inches diameter, when frequently a block only one inch thick yields thirty leaves. But when a large log of timber is to be cut into vene"rs, and the saw exceeds four feet in diameter, it is formed of segments firmly secured to an iron plate, whilst the timber has two motions, the one longitudinal and the other lateral, to advance it sideways between each cut. This latter object is effected by adjusting screws and worm wheels moved by a handle, which makes 50 or 60 turns to advance the log one inch, the veneer, as it is cut, being guided oft from the saw. There is a mode of superse ding the saw in veneer cutting, which has se veral times been proposed, and probably ori gmated in Russia, where a machine is em ployed capable of cutting an entire tree into one spiral veneer with a knife, as if the ve neer were uncoiled like a piece of silk from a roller. In France, the plan has been applied to iron and sheets obtained measuring 150 by 30 inches. This plan, however, is not adapted for brittle woods, and does not expose the most ornamental section to view, Which is the desideratum in veneers, on account of the purposes for which they are always employed, namely, fine cabinet work, and to give a superior appearance to the exterior of furniture. Circular saws have likewise been applied to cut off the ends of railway bars whilst red-hot, the saw making 1000 revolutions per minute, and having the lower ends immersed in water. Marble has, for several years, been exten sively sawn by machinery driven by steam power, although the processes are closely analogous to those pursued by hand. The ordi nary arrangement is to form a frame by fixing vertically four strong posts well connec ted together, within this the block of marble is placed, and over the marble is suspended the saw-frame, which reciprocates horizontal. ly, and rolls on pulleys which slide in verti. cal guides, and are suspended by chains con nected to a counterpoise weight, so adjusted as to allow the saw frame to descend when left to itself, and which supplies sufficient pressure for causing the penetration of the saws. The distances between the saws and their parallelism are adjusted by iron blocks, and every blade is separately strained by its wedge until sufficiently tense. The hlades, it must be observed, are merely slips of sott iron without teeth, so that the blade itself does not cut but simply serves as the vehicle for the application of the sand, which acts as the teeth of the saw, and performs the cutting process, the action of the saw being assisted by a small stream of water supplied from above. The introduction of the sand and water at the pro per time is the chief difficulty in stone-saw. ing, to allow the cutting material ready ac. cess beneath the edges 01 the saw blades, the frame is slightly lilted during each stroke, and by the usual system the end of the stroke is the period chosen, but a recent patent points at the central position as most eligible. The traverse of the frame is, perhaps, preferably given by a jointed connecting rod attached by an adjustable loop to a long vibrating pendu. lum put in motion by steam power. The cir. cular saw is also employed for cutting slabs of marble into narrow pieces, but although term-, ed a saw, in work of this kind it is, inrealit1 only a disc of iron without teeth, several of these being fixed on a revolving mandrel,whilst the mrrbJe is placed on a reciprocating bed which travels with a slow traversing move ment. (To be Cantinned.)
This article was originally published with the title "Machinery and Tools as they are.—Saws and Saw Mills"