The Sheffield grinders generally employ ash for the center blocks and wedges for grindstone spindles, and they mostly run all their stones and glazers in one set of holes, and adjust the length of the straps for various sized pulleys by using short pieces of strap of different lengths, which they apply by means of round buckles.
Between the standards and below the stone lies a long narrow water trough of wood lined with lead or of cast iron, sometimes called the "dog pan" but which should never contain enough water to reach the stone, as the centrifugal motion would splash the water about in an inconvenient degree; the water is therefore at intervals thrown on from a pail with the hand, or is allowed to flow from a thread-like jet on the side of the stone very near its periphery. The workman is seated astride a board called the horse, which rests behind on the bearers or sleepers of the frame, and in front is propped up by a transverse bar of wood, which is shifted to or from the stone, to adjust the front end of the horse to a convenient height, dependent on the diameter of the grind-stone.
The edge of the horse near the stone is commonly shod with iron, that it may be used for supporting the turning tool employed in turning up the grindstone, and the horse has mostly also a piece of leather or sacking or a sloping board to keep off the wet thrown up by the centrifugal motion. The framework is sometimes furnished with a splash-board, which is placed almost perpendicularly on the other end of the trough, and projects above the top of the stone, so as to catch most of the water that flies off and reconduct it to the trough; but the splash board is not always added.
9. - The Position of the Grinder when at Work is highly favourable, he is seated before and rather above the stone, with his feet resting upon the ground or other firm support, and in the act of grinding and polishing delicate works, they are held by both extremities in the two hands, whilst the elbows rest upon the knees, so that the grinder can thus keep his person very steady, and is enabled to feel with great delicacy and exactness the position of the work upon the stones or polishers. But in polishing the handles, springs, middle parts of pocket knives, and other small pieces the cutler frequently employs the grinding lathe just described in article 7.
10. - Large Grindstones for Heavy Edge Tools, Saws, Gun Barrels etc. Manufacturers in these branches use much heavier grindstones than cutlers, and mount them somewhat differently. Stones larger than 3 feet diameter and 4 or 5 inches thick, and those extending to the dimensions of 8 or 10 feet diameter, and 12 to 16 inches thick, are commonly wedged upon square spindles having cylindrical necks, that run on bearings either of hardwood or metal, and the pulley is generally placed at the extremity of the spindle and outside the one bearing, so that it may be changed agreeably to the decreasing diameter of the stone without the trouble of lifting the stone from its bearings, which is not commonly done until it is worn too small for its particular use. A deep groove is then turned in the periphery of the stone, and which, after removal from the spindle, is split in two by chisels and iron wedges to serve for smaller works.
The arrangements of the trough, horse and splash-board, for large grindstones differ principally in size alone from the preceding; frequently however the axis of the stone is level with the ground, and the bearings are fixed on two sleepers, between which the earth is simply excavated to form the trough, as the grinders' tools are generally of the most simple and inexpensive kind.
11. - Large Stones are always driven by Power, a drum of three to five feet diameter commonly extends across the grinder's shop, and the stones are arranged in a line on each side of the same. The surface velocity of the drum is commonly about 200 feet in a minute, and the diameter of the pulley being about one third that of the stone, the surface velocity of the latter is from about 500 to 600 feet a minute. This speed gives rise with large stones, to so much momentum as to endanger their being split, if there should be the smallest flaw in the stone, or that from neglect it acquires a heavy side, from being allowed to wear out of the true concentric figure. The centrifugal force then sometimes breaks the stone, and drives the huge fragments with frightful violence through the roof or walls of the building, to the occasional destruction of human life.
12. - Flanges and Rings to prevent Stones from Breaking. The liability of grindstones to be broken by excessive centrifugal force, is materially lessened if not altogether averted, when four or six holes are made through the stone, and iron plates or rings covering about one-third to one-half of the diameter are bolted on each side, sacking, felt, pitch or some soft materials being interposed, so that the stone and two side plates when bolted together, may form a compact solid mass; Flanges are also used as well as rings, but neither of them so generally as they ought to be, especially when from cupidity it is attempted to drive the stone as fast it will bear with hoped for safety, in order to hurry through as much work as possible.
In the new and unprotected stone, there is considerable body of the material or length of radius to withstand fracture, but when the stone is reduced to half its primary diameter, and its axial speed is doubled to maintain its original surface velocity, the risk is much increased, because there is then so much less bulk in the stone to resist accidental fracture.
13. - Engineers' Tool Grindstones or those employed for keeping in order their working tools; vary from two to five feet diameter, and four to eight inches thick, and as may be supposed, the structure of the framing is usually in metal, and much more engineer-like than the last. For instance, the trough is made either entirely of cast iron, or with cast iron sides united with a wide strip of boiler plate rivetted to each. The trough has usually feet to support the axis at two to two and a half feet from the ground, to suit the erect position of the workman, who holds the tool securely on a horizontal iron bar that is fixed near the stone, and at a con- I venient height by means of pedestals secured to the frame, this arrangement gives the choice of position in the rest or bar. The axis is cylindrical throughout, and the stone is fixed on its central part, as will be explained: the spindle lies in two plummer blocks or brasses, which are fixed on the edges of the trough, and one end of the spindle overhangs the same to receive the strap pulley, by which the stone is driven from the main shaft running through the building. There is likewise provision for changing the diameter of the pulley on the main shaft or on the spindle, to increase the velocity of the stone as it becomes reduced in diameter; but unlike the generality of machines in the engineers' shops, the grindstone does not require fast and loose pulleys to connect or disconnect it with the power, as from its frequent use it is kept continually running when the engine is at work.