This machine is shown in plan in fig. 1113, in which a represents the grindstone, and b the pulley to be ground, the pulley is mounted upon the mandrel c, which for the convenience of easy removal is fitted by a key into the spindle d, at the one end, and works through a plummer block e, at the other. The spindle d is fitted in bearings fixed on the frame f, which together with the plummer block e, are traversed simultaneously on longitudinal slide bars g, by three screws of equal pitch, each communicating by a pair of bevil wheels with a transverse rod A, having a wheel on its end to be moved by hand. By this arrangement the pulley admits of being gradually advanced in a parallel line, to keep its edge in contact with the stone as the grinding proceeds.
The spindle upon which the pulley is mounted, is reciprocated to and fro through its bearings, by means of a crank on the end of the shaft i, which is driven by a bevil wheel leading to a pinion fixed on the axis of the grindstone. The pin of the crank on the shaft i, works in a brass that slides in a perpendicular groove in the frame j, which is fitted between collars on the spindle carrying the pulley, and slides upon a parallel guide rod at the back. The revolution of the crank pin traverses the frame j, and the pulley spindle connected with it, and as the crank pin is fitted in a groove that admits of its being placed at any distance from the center, the amount of reciprocation may be readily adjusted to suit the width of the pulley. To allow of the crank being traversed longitudinally with the frame / carrying the spindle of the pulley, the crank shaft i is made to slide through the hollow axis of the bevil wheel, which is bored out of the proper diameter, and provided with a feather, that enters a groove extending throughout the length of the shaft, to cause its rotation.
Mr. Whitelaw also proposed another machine for grinding pulleys that are required to be rounded upon the edge instead of being cylindrical, this machine is very similar in its general arrangement to fig. 1113, but instead of the spindle carrying the pulley, being reciprocated in a straight line through the bearings, the revolving spindle is mounted in a swing frame having vertical pivots. The frame is swung horizontally backwards and forwards by an eccentric, so that the edge of the pulley in contact with the stone describes the arc of a circle, of which the vertical pivots are the center, and as the latter are fitted into grooves in the top and bottom of the swing frame, they admit of being adjusted to give any required degree of curvature to the edge of the pulley. The length of traverse of the swing frame is adjusted by attaching the connecting rod leading from the eccentric, at different distances from the center of motion.
In another machine for grinding cylindrical pulleys made by Messrs. Randolph Elliot & Co. of Glasgow,* the pulley to be ground is mounted on a mandrel revolving with moderate velocity in fixed bearings, and the grindstone which revolves with considerable rapidity is slowly traversed across the face of the pulley, by means of a screw passing through the hollow shaft of the grindstone, and driven by a system of differential wheels mounted on a sliding frame, that is shifted to and fro by hand, in order to reverse the motion of the screw. The grindstone is fitted in the center with a cylindrical bearing that slides upon the shaft, and the traverse motion is communicated from the screw to the grindstone by means of a nut having two flanges, that pass through longitudinal grooves in the hollow shaft, and are firmly fixed to the cylindrical bearing of the grindstone.
* See Practical Mechanic and Engineers' Magazine, Vol. IV. p. 73.
The bearings of the spindle carrying the pulley to be ground, are attached to a frame sliding horizontally, and adjusted by a single screw to bring the edge of the pulley in contact with the stone; and to keep the pressure uniform notwithstanding any trifling irregularities of the stone, a spring is introduced between the adjusting screw and sliding frame. As in Mr. Whitelaw's machine the axis of the grindstone and pulley are placed parallel to each other, and are driven in the same direction, so as to combine the velocity of the two surfaces.
Internal cylindrical surfaces such as the bearings for spindles, and similar works in iron and steel, are ground with cylindrical grinders, generally of lead or tin, but sometimes for greater durability and exactness brass or iron are employed. The grinders are in general made as solid cylinders of the required diameter, and a succession of grinders are employed each a little larger than the preceding, but sometimes the grinders are made with a small power of expansion in order to avoid the necessity for several grinders when the hole has to be materially enlarged.
Fig. 1114 consists simply of a bar of iron, upon the middle of which a lump of lead is cast and turned to the suitable diameter. This form of grinder is the most generally employed for cylindrical holes that pass entirely through the object, the iron bar upon which the grinder is cast, is made much longer than the hole to be ground, in order that it may be traversed endways through the hole to equalize its diameter, and prevent the formation of rings. When the hole is long and has merely to be corrected for trifling irregularities, the object is fixed horizontally in the vice, and the central rod of the grinder is grasped in a diestock or fitted with a pulley to serve as the handle. The grinder is then charged with emery, inserted in the hole, and worked backwards and forwards with a screw-like motion, the same as in grinding an external cylinder by hand; to facilitate the first entry of the grinder, it is made slightly taper at the front end. Small grinders soon become reduced in diameter by use, sometimes to compensate for the wear the grinder is laid upon the lathe-bearers or other support, and a few light blows of a hammer are given along one side to spread the metal out to a larger diameter. The two flat faces thus made along the sides of the grinder also serve to allow of the escape of the surplus emery, and with this view large grinders are frequently made with a few grooves along the sides.