51. - This title includes three different kinds of apparatus, all of which have wooden centers covered with leather, and are thence sometimes indiscriminately called buff wheels, but they are distinguished into three kinds as above by practical men, thus:

First. Buff wheels which are covered with thick soft leather, sometimes half an inch thick, the bull neck being commonly employed. In the metropolis old regimental belts are sometimes used from economical motives, instead of the new kinds of leather above named, but this seems to be a questionable policy, as the belt leather is less durable, and although it may serve for glazers, it is too thin for buff wheels. The coarse buff, or sand buff, is supplied with Trent sand and oil, the fine buff, with rottenstone and oil; these are not used for steel but for softer metal such as brass, Britannia metal, etc, and for horn, tortoiseshell and ivory. Secondly. Glazers are wheels covered with harder leather, upon the face of which emery is attached by glue, they are almost invariably used dry, and for steel. The leather used for glazers and polishers in the manufacturing towns of Sheffield and Birmingham is "beast hide," that is, the same leather which when hammered is used for the soles of shoes, the leather is cut into strips, and used without having been hammered, the thick and thin parts being selected according to circumstances; as glaze wheels require moderately thick leather supplied with emery; and polishers soft thin leather employed with dry crocus.

Thirdly. Polishers are wheels covered with thin soft leather, and supplied with crocus which is rubbed on dry, and without the intervention of glue or oil. In Sheffield one kind of leather is tanned expressly for polishers, it being important that the whole of the grease should be extracted, as if any remain in the leather it will not polish properly. The polishers are used alone for steel, and with very small velocity.

52. - The Smallest Buff Wheels, called bobs, are used in polishing the insides of the bowls of spoons - they are simply disks of leather, nearly an inch thick, known as sea cow or bull neck; they are perforated so as to be mounted on spindles, and are turned of a nearly globular form. See Albata.

53. - Buff Wheels and other Leather Wheels, with Wooden Centers differ much in size, those for cutlers usually measure from 1/4 to 4 inches wide by 4 to 20 inches diameter, although they are sometimes of twice that diameter; they have wooden centers or disks usually cut out the plankway of the grain, in similar woods to those used for glazers, but they are better when constructed of various pieces in sectors, the best mode being that recommended in article 41, or two layers of sectors each consisting of about sixteen pieces and glued up so as to break joint. The largest of these wheels, say those exceeding two feet diameter, are generally made up of one set of middle sector-like pieces, screwed fast between two circular iron plates which are themselves keyed on to the spindle, and then a set of felloes is nailed or screwed around the periphery on each side; making the thickness out to three, four, or even five inches. When the wood centers have been constructed according to some of the above modes, and turned cylindrical or rounded as the case may be, they are turned smooth on the edges and then covered with one thickness of leather.

54. - In Covering the Wheels, the wood, and also one side of the leather, are plentifully glued, the extremity of the leather is fixed down by two or three nails driven a little way into the wooden disk, the leather is stretched tight and nailed at short intervals, and its other end is also fixed down, and when the entire surface is covered with one strip if possible, the glue is allowed to dry. It is a matter of great importance that the ends of the leather should be made to butt closely one to the other to make good joints, otherwise the work jumps when a bad joint passes beneath it. The nails are afterwards withdrawn, the leather is turned true and regular with a flat chisel. Sometimes the glazers are required to be very hard, and in this case the leather is soaked in water for a few hours before being glued on the wheel, it is then secured as above whilst in the wet condition, and in drying the leather contracts and becomes considerably harder.

Buff Wheels even of the small diameter of 10 or 12 inches are frequently made three or four inches wide, and covered with soft leather half an inch thick. In such cases the thickness of the wood centers is also very nearly three or four inches, or the width of the leather, which however is allowed very slightly to project, and the sides of the wood are considerably hollowed in the sweep of a circle from the edge to the center to allow the works to be turned round on the edge of the leather in reaching into hollow and rounded angles, as already noticed the buff wheels are used either with Trent sand or rottenstone mixed with oil, and for various materials excepting steel.

Emery Wheels, when the leather with which they are covered has been turned smooth, are brushed over with glue, rolled in a heap of dry emery powder, and afterwards on a smooth board to consolidate the head and make the periphery smooth.

55. - Coarse Emery Wheels are always used dry, and they give off a splendid display of sparks with some of the risk of overheating the work that attends the use of the dry grindstone; the finer emery wheels are sometimes used just as explained with the wooden wheels, namely they are dressed with the emery cake, and bouldered down with the flint, to bring the head to a smooth and regular condition.

Tool makers use the buffs or glazers immediately after the grindstone, and select the coarse and fine buffs according to the degree of finish required. It may be observed the dry wheels give the brighter gloss, but do not generally leave the work so smooth as those which are greased.

56. - In Renewing the Face of the Emery Wheel, or in putting on a "new head," the wheel is wetted with a sponge and cold water, and allowed to soak for about an hour, the used emery is then scraped off with an old knife, and the surface of the leather is made somewhat rough; after which it is again glued, and rolled first on the emery and then on a flat board as originally. It is useless to attempt "to put one head upon another," or to apply new emery, until that which has been used has been thoroughly scraped off.

57. - The Polishers for Razors and Fine Cutlery are soft leather wheels charged with crocus, which are always used dry. It is necessary that both the polisher and blade should be hot, as without a moderate and equal degree of heat, short however of that producing a colour on the steel, the process does not succeed, and a good polish is not produced. It is therefore usual with some workmen before commencing work to take a piece of razor steel, which is held against the revolving polisher to prepare it for the work itself, by crushing and regulatir, the powder with which the polisher is charged. 58. - Action of the Polisher. - Although the polisher is made to revolve much more slowly than the other wheels, the razor is moved to and fro from end to end, very quickly and with considerable pressure, to distribute the heat equally; and the blade is not drawn slowly across and off as in lapping, on the contrary the work is moved endlong actively, and pulled off quickly. In examining the work, the polished part is occasionally wiped clean with the patch or thick piece of cloth or felt, which serves both to protect the fingers from the heat of the blade, and also to supply the polisher with crocus, as the patch is dabbed upon a small quantity of dry crocus close at the workman's hand, and is then rubbed on the polisher, to transfer the powder to the wheel.

Occasionally the surface of the polisher becomes very hard from being somewhat scorched by the heat generated in polishing, and its surface is then more or less filled with scratchy lines which disfigure the blade, at such times the wheel is stopped, and the face of the polisher is roughed up, or thoroughly scraped with an old razor blade or knife as in erasing writing, in order to remove all the old head or polishing stuff, and render the leather a little rough, and quite soft; after which the polisher is recharged by means of the thumb or patch.

59. - The Flat Sides of Wheels are not often covered with buff leather except by lapidaries, but in imitation thereof glass and emery paper are frequently glued on flat chucks of wood and used for finishing the flat surfaces of small works in the metals, woods, ivory, and other substances, and Mr. Larkin dusted the naked wood with a covering of pulverised flint, as noticed in the previous article on Flint.

60. - A Flat Polishing Machine actuated by rotary motion is used in America for flat works, such as brass hinges, parts of locks and other metal works. The principal part consists of an endless strap of leather, which is put in motion by its encircling a foot wheel as in a lathe, but the strap instead of giving motion to a pulley, passes over and in contact with a narrow flat board, the edges of which are rounded or furnished with small cylindrical rollers to lessen the friction, sometimes two oblong holes are simply made in the bench. The strap is charged with emery glued on exactly as in the emery wheels or buffs. The work when applied on that part of the strap which is flowing over the flat surface of the board is polished with considerable rapidity and a tolerable approach to a plane surface.