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Saws and Their Manufacture
The saw had ever played a most conspicuous part in the economy of manufactures, and its importance will readily be admitted, when we consider how essential a bearing it has upon our every-day life, and how conducive it is to the development of those useful arts upon which, to a great extent, the very existence of civilized humanity depends. Its extended and universal employment in the higher class of industrial art has, in great measure, contributed to the advancement of civilization and prosperity, by administering to the production not only of those things which are necessary to our being, but of those which tend to cultivate the taste and to refine the mind. The art of sawing must have been known at an exceedingly remote period (even, it is probable, in prehistoric times), as it is impossible to suppose that such magnificent and gorgeous structures as are described in the Hebraic Scriptures, and elsewhere, could have been formed without some knowledge of the use of the saw; but the full extent to which that knowledge existed, and the modes of its practical application, cannot be educed from the insufficient evidence at our command in these times. The ancient Greeks ascribed the invention of the saw — as also the chisel, compasses, and auger, with other implements — to Daedalus (or, as some say, Talus), or his disciple Perdix, renowned architects and sculptors, who were accustomed to employ these instruments in the production of the Daedali - wooden images of the gods, ornamented with gilding and real drapery, and usually represented standing with the feet in an advancing posture. There is every reason to believe, however, that the derivation of saws is infinitely more remote, as they have been discovered clearly represented in the midst of the hieroglyphics inscribed on the obelisks of Egypt. According to the hypotheses of sundry ancient writers, the jaw-bones of the snake with its teeth, or the vertebral of a fish with its protruding small points, first suggested the plan of the saw; but it is equally as likely that a common brier upon some antique "genius" may have torn his flesh, or his fig leaves, if he wore any, may have suggested the idea. The great wonder is, so useful an implement is the saw, that we have not been assured by some ancient writer that the notion of the saw was divinely inspired. The Greeks did indeed deify the supposed inventor of the saw, thus intimating that, in their opinion, the conception of it was beyond the powers of the human mind. The saws used by the Grecian carpenters were made like the straight frame instruments of modern days, the blade having been set across the middle of the frame, with the teeth perpendicular to the plane. The block of wood was held down upon a table or bench by clamps, and the sawyers, on opposite sides of the bench, at each end of the saw, pulled it back and forth. The investigation of the history of the saw affords an interesting field to the archaeologist, although the materials or means of information are limited, so far as specific facts are concerned; but there is wide scope for intelligent inference. But such investigation, thoroughly carried out, and the results thereof stated, would hardly come within the purview of this article, which is intended in the main to be utilitarian. Those who desire to make more extended researches are referred to Beckmann's "History of Inventions", containing an account of the earlier saw-mills, together with certain speculations on the origin of the saw. Emy, in his "Traite de l'Art de la Charpenterie," also makes some allusions to the same subject of an instructive character, as likewise does Holtzapffel, in the second volume of "Turning and Mechanical Manipulation", and Karmarsch in the "Handbuch der mechanischen Technologic", vol. 1 Hanover, 1866. Saws are made of the many forms and sizes required by thousands, according to the particular purposes for which they are designed ; and hardly any instrument for man's use is more varied in size than the saw, when we consider the full range of its species, so to speak, from the watchmaker's delicate saw for piercing and inlaying, which measures about one thirtieth of an inch in width, and one hundredth of an inch in thickness, up to the immense mill and mulay (mullet ?) saws in use in certain portions of America, and the peculiar band-saws in combination with rack-benches, employed in ripping logs of timber of almost any dimensions. The oldest forms of the saw are made of a straight piece of steel, "toothed", and set in a frame, or with handles on either end, to be moved by one or two persons, according to the form given; or the saw-plate is made sufficiently stiff to be propelled by one handle, and worked by a single person holding it in one hand, like the saw most in use among joiners and carpenters in general. In modern times has been invented the circular saw-blade, which revolves, and with its teeth in the periphery, may be made to cut with incredible speed; a saw of two feet in diameter, for example, being driven at the speed of from two thousand to twenty-four hundred revolutions a minute. But the chief important improvement, for a long time, relating to saws, is one recently devised by Mr. Henry Disston, of Philadelphia (and patented January 14, 1868), which, since it comprehends one of the most valuable achievements of progress, in any art, namely, economy of means or in products, is highly worthy of note. To make this great improvement most clear to the reader, it should first be observed that the rapid wear of circular saws demands the frequent sharpening of their teeth; and that this, in ordinary saws, not only requires tedious manipulation, but results in the rapid reduction of the saw in diameter. To rescue the saw from this rapid reduction is the object of Mr. Disston's successful invention. The better to explain this great improvement, we introduce the two accompanying cuts, designated "Fig. 1" and "Fig. 2", respectively. (For the use of the plate of the latter we are indebted to the courtesy of Messrs. Henry Disston & Son, of Philadelphia).
Fig. 1 represents a portion of a circular saw with ordinary teeth, which must be sharpened by reducing both the front edge a and back b of each tooth; a duty which requires much time, and which cannot be performed without much waste of material, as will be readily understood by reference to the dotted lines, which illustrate the condition of the blade and waste of material after frequent sharpening. To obviate these objections or difficulties was devised the plan above alluded to, and shown by Fig. 2, by which it will be observed that the back of each tooth is a continuation of a curved line, Z, spirally arranged on the blade, and that the sharpening of the tooth is accomplished by the reduction of a portion of the front or throat only; thus, in reducing the tooth, the course pursued by the cutter (the contrivance by which the tooth is cut) is spiral, so that while the rotary cutter is in the act of reducing the front of the tooth, D, it is at the same time prolonging the back of the tooth, C, prior to the reduction of the front of the same. The teeth can be sharpened from time to time, by simply filing the bevelled ends (as seen in Fig. 2); and this mode of sharpening may be continued until the bevelled point of each tooth reaches nearly to the end of the throat, when by means of a rotary cutter a further portion of the throat may be removed.
Fig. 2 (representing the so-called " Patent Gullet-Tooth Circular Saw", secured by patent to Messrs. Henry Disston & Son) further illustrates, in its double capacity, a saw, B, as worn down from a larger saw, A, the teeth having been "carried back", or cut (by the use of the same firm's patent "gummers"), on the periphery lines, Z, instead of on the centre line, G, by the old method of filing. The engraving represents a two inch tooth or gullet. When the saw has been worn down by this method from C to F, on centre line, it has been reduced but six inches, but has presented a point or cutting surface on the periphery line from G to Y, a distance of twenty-four inches. The majority of saws, however, are run successfully with a one and one-fourth inch tooth; and of course the smaller the gullet the less the waste of the saw.
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