The circular cross cutting saw. The reader must figure to himself a frame formed of two long parallel spars of wood, united by cross bars and braces ; this, which we call the saw frame, is suspended vertically •by one end, where it is jointed to the end of a similar frame, (say the upper frame,) poii.cd nearly horizon tally, on an horizontal axis which passes through it ' near the middle of its length. The end opposite that -which supports the saw frame is loaded, so as to coun • terpoise its weight. At the lower end of the saw frame, -the spindle of the saw is mounted, by its bearings be ing bolted on the spare of the frame. The saw is fixed on the extreme end of the spindle, so as to be on the outside of the spars. The spindle is parallel to the axis of the upper frame. The tree is placed on a bench, and drawn up to a stop by a windlass, just the same as in the foregoing machine, and is kept steady by a crooked bar in a similar manner. The tree lies in a direction parallel to the axis of the saw. Now it will be seen by this arrangement, that the saw possesses universal motion ; but the axis is always parallel to itself, and the saw in the same plane. It can be raised up or lowered down, by inclining the upper frame on its axis ; and to move it sidewise, the saw frame must swing sidewise on its joints, which connect it with the upper frame. These movements are effected by two winches, each furnished with a pair of eqiial pi nions, working a pair of racks fixed on two long poles. The spindles of these winches are fixed in two vertical posts, which support the axis of the upper frame. One of these pair of poles are jointed to the extreme end of the upper frame ; therefore by turning the handle belonging to them, the frame and saw is elevated or depressed : in like manner, the other pair are at tached to the lower part of the saw frame, so that the saw can be moved sidewise by means of their handles, which then swing the saw from its vertical position.
These two handles give the attendant a complete command of the saw, which we suppose to be in rapid motion, the tree being brought forwards and properly fixed. By one handle, he draws the saw against one side of the tree, which is thus cut into, (perhaps half through ;) now, by the other handle, he raises the saw up, and by the first-mentioned handle he draws it a cross the top of the tree, and cuts it half through from the upper side; he then depresses the saw and cuts half through from the next side ; and lastly a frilling cut of the saw, as the lower side completely divides the tree, which is then advanced to take another cut. The strap for the saw is conducted over gullies, two of which are fixed on the upper frame near its ho rizontal axis ; and it then turns a pulley, fixed on an axis concentric with the joint, connecting the two large frames. On the same axis is another equal pul ley, around which the strap is passed, which turns the pulley on the spindle of the saw. By this means, the strap never becomes slack in any movement of the saw, as its points of flexure are the same as the frames. This machine is very ingenious, and acts with great accuracy, and astonishing rapidity.
The great reciprocating saw is on the same prin- ' ciple as the saw mill in common use in America, at least the differences are so small, that they cannot be explained without drawings ; and as this machine is by no means essential to the manufacture of blocks, we shall refer our readers to the article SAWING Ma chinery.
The circular ripping saw, is a thin circular plate •• of steel, with teeth similar to those of a pit saw, form- f ed in its periphery. It is fixed to a spindle placed s horizontally, at a small distance beneath the surface of a bench or table, so that the saw projects through a crevice a feNJ inches above the bench. The spindle
being supported in proper collars, has a rapid rotatory motion communicated to it by a pulley on the opposite end, round which an endless strap is passed from a drum placed overhead in the mill. The block cut by the preceding machine, from the end of the tree, is placed with one of the sides flat upon the bench, and thus slides forward against the revolving saw, which cuts the wood with a rapidity incredible to any one who has' not seen these or similar machines. The wood is guided in its progress toward the saw by a large parallel ruler, similar to that used for drawing, which can be placed and fixed at any re quired distance from the plane of the saw, but is al ways parallel to it : by this means the circular saw becomes a general machine, and can be adapted to cut any required width. Its great advantages are, the saving of labour, and the great accuracy of its performance, as it invariably cuts a perfectly plane surface ; and it is evident that any number of pieces cut by it must be of precisely the same size, when the parallel ruler remains fixed at the same point. This is an important circumstance in these works, as the accurate performance of many, or indeed all the ma chines, depends upon the blocks which are submitted to them, at the same time, being of one size. We have not given these sawing machines among our Plates in this article, because this saw is in constant use for sawing in general, and will therefore come more pro perly under SAWING Machinery, where we pro pose to explain this, or a similar one constructed by Mr Maudslay, who has a peculiar mode of making the collars for the axis of the saw, which succeeds remarkably well. It is a great improvement upon • the usual mode of fitting up the circular saw, and which, we believe, was first introduced (at least for sawing large timber) by Mr George Smart of Lon don. In the old method, the ends of the spindle were perforated with small conical holes, and the conical points of two fixed screws were inserted into them. All the points of contact were made of steel, and hardened. Nothing could be more perfect or easy than the movement of such a spindle, until it was put into rapid motion by the machinery, when, ha ring- a considerable strain on the pivots from its work, it required a constant supply of oil, which was very quickly consumed, as the centrifugal force tended to draw the oil up the largest part of the cone, and consequently take it from the points of contact. If the machine continued to work without oil, the great velocity and pressure would cause such a friction, as to warm one or other of the steel joints. This would at once expand and soften it, so as to increase the fric tion in a two fold degree ; and if this evil continued, the point would suddenly become red, or even white hot, and being too soft to resist the power of the saw, would then be twisted off. The broken point when cold,• would then be found so jambed, or ra ther welded, into the hole in the end of the spin dle, that it would be impossible to get it out except by drilling. The improved spindles, 'as constructed by Mr Maudslay, have double conical sockets, so dis posed as to-attract the oil into the fitting, instead of throwing it. out. For small saws, where the strain is but slight, the old method is as good as can be de vised. The blocks applied to the ripping saw are first split or ripped, in the direction of the grain, into the proper breadth in one direction, and then in the other, so as to reduce them proper scantling for the various sizes of blocks.