To explain the mechanism by which the cutters are advanced, we must refer to Figs. 2, 3, and 4; 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 j divided by a longitudinal aperture cc, Fig. 4, on each j side. At the ends it is left a complete tube, to keep ] the two halves together. The cutter head KK, LL, consists of two parts,—of a tube KK fitted upon the axis D with the greatest accuracy, and of a cast iron ring LL fixed upon KK by four wedges. On its cir cumference are eight notches, to receive the cutters or steelings ,f,f, 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 ee, which are put through 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 0 : the axis of the pinion and roller being supported in a framing attached, to the standard BB, as shewn in the perspective view of the machine in Fig. 5. 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, su perior 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 fix ed at the right hand extremity D, of the bar DD, Fig. 4. Another pillion is fastened on the extremity of an axis, analagous to the rack M, having at its other extremity a small screw, which works in a fe male screw, fixed to the cutter KK at e, (Fig. 2.) Below the second pinion is another containing 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 driven by the first pinion at the end of the hollow axis DD. The first pinion has 26 teeth, the fourth 30, and the second and third may have any number, provided they are equal. As the axis DD revolves, the first pinion fixed on its ex tremity drives 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 ex tremity, and of course makes the cutter advance along the cylinder. This screw has eight threads in an inch, and sixty turns of the axis arc required to cut one inch.
To introduce a cylinder into its place in the ma china, it is necessary to remove the upper braces ll of the bearings, upon the standards BB ; and by sup porting the axis upon blocks placed under the mid dle of it, the standard, with the pinion N and roller frame, is removed, by taking up the nuts which fas ten it down upon the ground sills AA, the rack M being supposed previously withdrawn. A cutter
block L, of the proper size to bore out the intended cylinder, is now placed upon the slider K, (Fig. 4.), 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..5, the cylinder being by estimation adjusted concentric with the axis i D. Two bars of iron are now wedged into the aper tures c, c 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 driven round the cylinder to adjust it with the utmost accuracy ; and in this state the cylinder is ready for boring.
The next operation is fitting the cutters, which are fastened into the block L by wedges, and adjust ed by turning the axis round, to ascertain that they all describe the same circle. The boring now com mences 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 cut ters are drawn 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 two operations are sufficient ; but the best cylinders are bored many times, in order to bring them to a pro per cylindrical surface. The last operation is turn ing the Ilaunch 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 per pendicular to the axis of the cylinder. The cylinder is now finished and removed.
The accuracy of this machine depends on the bo ring 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 in 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. 1. The pinion 30 is supposed to be on the axis of a water wheel, and turns the two wheels 60, 60, which have project ing axes, with a cross cut similar to the head of a screw, as is shewn 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. (J. F.) (0)