A few years ago (about 1824), Mr. Robert Eastman, of Brunswick Maine, U. S., invented some improvements in the construction of circular saws, and in the mode of sawing "lumber" (timber), which obtained extensive adoption in America; and as we think them extremely interesting, and that their adoption in this country would tend to beneficial results, we shall here annex the description, and the intelligent inventor's remarks upon the subject. Instead of a continued series of teeth all round the periphery of the plate, like other circular saws, Mr. Eastman's has only eight, or rather it may be said to have only four cutting instruments, each containing two teeth, which are placed at equal distances on the circumference, and projecting from it; these instruments are called "section teeth." The saving of labour in consequence of this form of saw is calculated at full three-fourths; and the surface of the timber is much smoother than when cut by the full-teethed saw. On the saw-plate are also fixed instruments called "sappers, " which, being placed nearer to the centre, do not enter the wood so deeply as the saw, and are adjusted so as merely to cut off the extraneous sap part, rendering the edges of the planks uniformly straight, and all the cuts of equal dimensions.
To understand which, it is, perhaps, necessary here to explain to the reader that the logs are, by this machinery, cut up lengthwise, not through the log, but from the circumference, or exterior, to the centre, as the radii of a circle, it having been ascertained that planks, staves of casks, etc, cut out in this manner, possess much more durability, strength, and elasticity, than by the common method. Fig. 1 represents a side view of the machine, with a log in it ready for working. Fig. 2 is an end view of the same, exhibiting the log partly cut into sections. Fig. 3 is the saw, with its section teeth LLLL, and its sappers M M. Fig. 4 shows the shape of the sapper, with a groove, or slit, to admit of its being set according to the intended width of the plank.
A, Fig. 1, is a strong frame of timber, about twenty-four feet long, by five broad, the ends of which are seen at A A, Fig. 2. B, Fig. 1, is the carriage, about twelve feet long, and four broad, the ends of which are seen at B B, Fig. 2; it travels upon iron truck-wheels, grooved on their circumferences, and run upon iron slides, as shown at K K, Fig. 2. C. Figs. 1 and 2, gives two views of the log under operation.
The log is fixed into the carriage by means of iron centres, upon which it also revolves, after each succeeding cut. At D D, Figs. 1 and 2, is seen part of the saw. At E E, Figs. 1 and 2, are situated the feed pulley, and shifting gear F, regulating pulleys. G is an index for regulating the dimensions of the cuts. H, revolving levers and pins. I, the pin and fulcrum of the levers. J J, the stirrup screws and pins.
Nearly in the middle of the frame is fixed the main shaft, of cast iron, which runs upon friction rollers, supported by stands on the floor. On this shaft is the saw, with its sappers and section-teeth. The motion is given by a band passing round the main pulley, and round a drum that runs under it; which may be driven by horse, steam, or water power. The method by which the saw is fed with the wood to be cut, and the return of the carriage for the succeeding cut, is too similar to our own to need a particular description. Its various arrangements are ingeniously contrived, and it may be justly termed a self-acting machine, for when once set in motion, no other aid than the power which drives it is requisite to its cutting a whole series of boards, of uniform dimensions, all round the log, having their thin-edged sides attached to the centre-piece. These boards being removed, a second series of boards may be cut in like manner to the former, provided the log is big enough.
"This machine," Mr. Eastman says, "furnishes a new method of manufacturing lumber for various useful purposes. Though the circular saw had previously been in operation in this country, and in Europe, for cutting small stuff, it had not, with the knowledge of the writer, been successfully applied to solids of great depth; to effect which, the use of section-teeth are almost indispensable.
"In my first attempts to employ the circular saw, for the purpose of manufacturing clap boards, I used one nearly full of teeth, for cutting five or six in depth, into fine logs. The operation required a degree of power almost impossible to be obtained with the use of a band; the heat caused the plate to expand, and the saw to warp, or, as it is termed, ' get out of true.' To obviate these difficulties, I had recourse to the use of section-teeth, and the improvement completely succeeded. The power required to perform a given quantity of work by the former method, was by this diminished at least three quarters. The work, formerly performed by seventy or eighty teeth, was, by the last method, performed by eight teeth; the saw-dust, which before had been reduced to the fineness of meal, was coarser, but the surface of the lumber much smoother than when cut with the full-teethed saw. The teeth are made in the form of a hawk's bill, and cut the log up, or from the circumference to the centre. The saw may be carried by an eight-inch band, and when driven a proper speed (which is from ten to twelve hundred times per minute) will cut nine or ten inches in depth into the hardest white oak timber with the greatest ease.
The sappers, at the same time, cut off from one to two inches of the sap, and straighten the thick edges of the lumber.
"The facility with which this saw will cut into such hard materials, may be supposed to result from the well-established principle, that where two substances in motion come in contact, their respective action on each other is in direct proportion to their respective velocities; thus, a circular plate of iron put into a quick rotary motion, will, with great ease, penetrate hardened steel, or cut through a file when applied to its circumference; and the same principle is applicable to a saw for cutting wood. The requisite degree of velocity is obtained by the continuous motion of the circular saw, by which also it has greatly the advantage of one that has but a slow motion, on account of dulling; as the teeth are but little affected, and being only eight in number, but a few moments' labour is required to sharpen them. If the velocity of the saw were slackened to a speed of but forty or fifty per minute, it would require at least four such bands to carry it through a log as above described.