are drawn to a scale. In fig. 314, A A denote two oak ground sills, which are firmly bolted down, parallel to each other, upon sleepers let into the ground. At each end of these a vertical iron frame, B B, is erected, to support the gudgeons at the end of a long cylindrical axis, DD, which is turned round by the mill. The cylinder LL, which is to be bored, is fixed immovable over the bar, and exactly concentric with it. A piece of castiron K K, LL, (figs. 310, 312, and 313,) called a cutter-head, slides upon the axis, and has fixed into it the knives or steelings ƒƒƒ, which perform the boring. This cutter-head is moved along the bar by machinery, to be hereafter described; by means of which it is drawn or forced through the cylinder, at the same time that it turns round with the axis D. The steel cutters will necessarily cut away any protuberant metal which projects within the cylinder, in the circle which they describe by their motion, but cannot possibly take any more.

The cylinder is held down upon an adjustable framing, which is ready adapted to receive a cylinder of any size within certain limits. Pieces of iron, E E, are bolted down to the ground sills, having grooves through them to receive bolts, which fasten down two horizontal pieces of cast-iron FF, at right angles to them. These horizontal pieces support four movable upright standards GG, which include the diameter of the cylinder LL which is supported upon blocks, bb, below, and held fast by iron bands aa, drawn by screws in the top of the standards GG. The cylinder is adjusted, to be concentric with the axis D D, and held firmly in its place by means of wedges driven under the blocks and the standards.

To explain the mechanism by which the cutters are advanced, we must refer to figs. 311, 312, and 313, by the inspection of which it will be seen that the axis DD is, in fact, a tube of cast-iron, hollow throughout. It is divided by a longitudinal aperture cc, fig. 310, on each side. At the ends of it is left a complete tube, to keep the two valves together. The cutter-head KK, LL, consists of two parts; of a tube K fitted upon the axis D with the greatest accuracy, and of a cast-iron ring LL, fixed upon KK by four wedges. On its circumference are eight notches, to receive the cutters or steelings ff, which are held in and adjusted by wedges. The slider K is kept from slipping round with the axis, by means of two short iron bars e e, which are put through to the axis, and received into notches cut in the ends of the sliders KK. These bars have holes in the middle of them to permit a bolt at the end of the toothed rack L to pass through. A key is put through the end of the bolt, which, at the same time, prevents the rack being drawn back, and holds the cross bars ee in their places. The rack is moved by the teeth of a pinion N, and is kept to its place by the roller O; the axis of the pinion and roller being supported in a framing attached to the standard BB, as shown in a perspective view of the machine in fig. 314. The pinion is turned round by a lever, put upon the square end of the axis, and loaded with the weight P, that it may have a constant tendency to draw the cutter through the cylinder. This lever is capable of being put on the square end of the axis either way, so as to force the rack back into the cylinder if necessary.

In some boring machines, another contrivance, superior perhaps to what we have now described, is employed to draw the cutter through the cylinder. It consists of four small wheels, one of which is fixed at the right-hand extremity, D, of the bar DD, fig. 314. Another pinion is fastened on the extremity of an axis, analogous to the rack M, having at its other extremity a small screw, which works in a female screw, fixed to the cutter K K at e, fig. 310. Below the second pinion is another, con

taining the same number of teeth, and fixed on a horizontal axis parallel to DD. At the other end of this axis is a fourth pinion, which is drawn by the first pinion at the end of the hollow axis DD. The first pinion has twenty-six teeth, the fourth thirty, and the second and third may have any number, provided they are equal. As the axis D revolves, the first pinion fixed on its extremity draws the fourth, which by means of the third, fixed on the same axis with it, gives motion to the second. The second pinion being fixed to an axis within DD, unscrews the screw at its other extremity, and of course makes the cutter advance along the cylinder. This screw has eight threads in an inch, and sixty turns of the axis are required to cut one inch.

To introduce a cylinder into its place in the machine, it is necessary to remove the upper braces, 11, of the bearings upon the standards BB; and by supporting the axis upon blocks placed under the middle of it, the standard, with the pinion N, and roller frame, is removed by taking up the nuts which fasten it to the ground sills A A, the rack M being supposed previously withdrawn. A cutter-block L, of a proper size to bore out the intended cylinder, is now placed upon the slider K, fig. 313, and wedged fast. The cutter-head is then moved to the farther end of the axis, and the cylinder lifted into its place. The standard B is returned, and the whole machine brought to the state of fig. 314, the cylinder being, by estimation, adjudged concentric with the axis D. Two bars of iron are now wedged into the ec in the axis, and applied to the ends of the cylinder; while the axis is turned round they act as compasses to prove the concentricity of the cylinder. Small iron wedges are drawn round its cylinder to adjust it with the utmost accuracy; and in this state the cylinder is ready for boring.

The next operation is felling the cutters, which are fastened into the block L by wedges, and adjusted by turning the axis round, to ascertain that they all describe the same circle. The boring now commences by putting the mill and axis in motion, and the machine requires no attention, except that the weight P is lifted up as often as it descends by the motion of the cutters or steelings. When the cutters are drawn down through the cylinder, they are set to a circle a small quantity larger, and returned through the cylinder a second time. For common work these operations are sufficient; but the best cylinders are bored many times, in order to bring them to a proper cylindrical surface. The last operation is turning the flanch n of the cylinder perfectly flat, by wedging a proper cutter into the head. This is of great importance to ensure that the lid will fit perpendicular to the axis of the cylinder, The cylinder is now finished and removed.

The accuracy of this machine depends on the boring bar, DD, being turned upon its own gudgeons; and if it is turned to the same diameter throughout, it will certainly be perfectly straight. While the axis is in the operation of turning, a piece of hard wood should be fitted into the grooves of the cylinder. The slider K is first bored out, and

afterwards ground upon the axis with emery to fit as true as possible.

The elevation of a mill proper for moving two of these machines, is represented in fig. 310. The pinion 30 is supposed to be on the axis of a water-wheel, and turns the two wheels 60, 60, which have projecting axes, with a cross-cut similar to the head of a screw, as is shown in the figure.

The ends of the boring axes have similar notches, and by putting keys in between them, the motion may be communicated or discontinued at pleasure, by the removal of the key.

FILE-CUTTING MACHINE.

THERE have been various contrivances for this purpose; but the best we are acquainted with is described in the Transactions of the American Philosophical Society, and is as follows:

AAAA, fig. 315, is a bench of seasoned oak, the face of which is planed very smooth. BB BB the feet of the bench, which should be substantial. CCCC the carriage on which the files are laid, which moves along the face of the bench A A A A, parallel to its sides, and carries the files gradually under the edge of the cutter or chisel HH, while the teeth are cut; this carriage is made to move by a contrivance somewhat similar to that which carries the log against the saw of a saw-mill, as will be more particularly described. DDD are three iron rods inserted into the ends of the carriage CCC C, and passing through the holes in the studs E E E, which are screwed firmly against the ends of the bench A A A A, for directing the course of the carriage CCCC, parallel to the sides of the bench. FF two upright pillars, mortised firmly into the bench A A A A, nearly equidistant from each end of it, near the edge, and directly opposite to each other. G the lever or arm which carries the cutter H H, (fixed by the screw I,) and works on the centres of two screws K K, which are fixed into the two pillars FF, in a direction right across the bench A A A A. By tightening or loosening these screws, the arm which carries the chisel may be made to work more or less steadily. L is the regulating screw, by means of which the files may be made coarser or finer; this screw works in a stud M, which is screwed firmly upon the top of the stud F; the lower end of the screw L bears against the upper part of the arm G, and limits the height to which it can rise. N is a steel spring, one end of which is screwed to the other pillar F, and the other end presses against the pillar O, which is fixed upon the arm G; by its pressure it forces the said arm upwards until it meets with the regulating screw L. P is an arm with a claw at one end marked 6, the other end is fixed by a join: into the end of the stud or pillar O, and, by the motion of the arm G, is made to move the ratch-wheel Q. This ratch-wheel is fixed upon an axis, which carries a small trundle-head or pinion R, on the opposite end; this takes into a piece SS, which is indented with teeth, and screwed firmly against one side of the carriage CCCC; by means of this piece motion is communicated to the carriage. F is a clamp for fastening one end of the file ZZ in the place or bed on which it is to be cut. V is another