Engineers mostly fix the stone between cast-iron flanges or plates, the one keyed on the spindle against a shoulder, the other forced up by a screwed nut or key passing through a diametrical mortise in the spindle. Mr. Roberts of Manchester prefers the latter mode, and in hanging the grindstone he fits a square piece of wood into the eye of the stone, then bores it to fit the spindle, and afterwards having smoothed the central parts of the sides of the stone, he inserts two disks of soft pine wood between the cast-iron flanges and the stone, - the wood adapts itself to the trifling irregularities of both parts, and serves as a somewhat elastic cushion to ensure contact, and consequently a firmer grasp on the stone, to the extent of about one-fourth of its diameter, to which the flanges extend; - by these precautions accidents rarely occur. Engineers sometimes use stones of the before-mentioned diameter of 8 or 10 feet for brightening the coarser parts of machinery, and such large stones are mounted nearly the same as those just described, but nearer to the ground.
14. - Turning up Grindstones. - As soon as the stone is wedged truly on its axis, it is turned on the cylindrical edge or face, and part way down each side. This is done with a rod of iron or steel drawn down at the end to about 3/19ths to 3/8ths of an inch square. The tool is not held radially but pointed downwards, at an angle of about 20 degrees, and is continually rolled over and over to present a new angle, which in its turn is rapidly worn away. The process is nevertheless much quicker than might be supposed.
In turning small grindstones driven by the long wheel, the stone is moved the reverse way, and more slowly than in grinding, so that the horse may be used for supporting the turning tool. In turning large grindstones driven by power, in which case the motion cannot be so readily reversed nor slackened, the workman goes to the back of the stone and supports the tool upon a wooden or iron bar placed across the water trough, and employs a larger pulley than for grinding. Sometimes a cross strap is allowed to run upon the edge of the stone itself, to reverse and reduce the speed of the stone when it is turned after having been mounted.
Large stones are seldom turned up, except when they are first set to work, but they are retained of a cylindrical or slightly convex figure, almost exclusively by the following process: -
15. - Hacking Grindstones. - At intervals during the time a large grindstone is in regular work, the strap is flung off and the stone is retarded by still applying to its surface the article to be ground; but before the stone comes to rest, the high places are marked at six or more parts of its width, by holding a piece of chalk or charcoal steadily upon the horse, and gradually approaching it so as to mark the more prominent parts. When the stone has stopped, the grinder hacks or notches the high places denoted by the marks, by means of a tool called a "hack hammer" which is like a small adze of 2 or 3 lbs. weight, but longer and more curved in the blade, and with a very short handle. The grinder cuts with the hack hammer shallow oblique furrows about one inch asunder and crossing each other, producing a chequered surface.
When the stone is again used, the greatest wear occurs at these roughened places, and by a continual recurrence to the dressing the circularity of the stone is sufficiently well preserved, and with but little interruption to the work. It is very impolitic to defer the dressing too long, for fear of giving the stone a heavy side, and risking its safety.
16. - Straggling or Ragging. - This process is principally adopted on fine and smooth grindstones into the surfaces of which particles of iron or steel have become embedded, and which greatly impede the action of the stone. In straggling, or ragging, the stone is kept running as usual whilst a piece of soft iron about a quarter or half an inch square, held upon the horse like the turning tool, is wriggled against the edge of the stone by a motion of the wrist, as in using a brad-awl, the iron is applied all over the surface, and lastly the edge of the bar is wriggled obliquely upon the top of the stone. This process also assists in correcting small inequalities in the figure of the stone.
17. - Turning and Roving Smooth Grindstones. - A different and perhaps more general mode of keeping the stone in order, especially when it is driven by the hand wheel, is followed by other workmen.
The motion of the stone is reversed, and the edge is turned with a bent tool, usually made out of an old file, by forging the end taper and to a thin wide chisel edge, and about one inch of the tool is then turned up nearly at right angles to the stem of the file. This tool is used as a hooked turning tool upon the horse, and it scrapes the surface tolerably true and smooth, and afterwards whilst the stone is at work its edge is cleared with the roving plate, a piece of either iron or steel plate just like a joiner's scraper, held upon the top of the stone not quite perpendicularly but meeting the stone at a small angle.
From its unstable position the roving plate chatters and jumps, and appears to fill the stone with minute furrows from dislodging some of the particles from its gritty surface. This mode also gives the stone a tooth, and as well as the last method serves to clear the stone from the thick dirty water or slush that otherwise fills its grain and considerably retards its action, frequently also the grinder throws a small handful of water on the stone, and applies his open hand very gently upon the same, in order to wash off the loose muddy coating it acquires whilst in use.
18. - General Remarks on Using Grindstones. - In order to avoid the wasteful destruction of the stones they should be exposed to as equal circumstances as possible; thus they should in the first instance be selected free from hard veins that impede, or flaws that accelerate the wear at the respective parts.