Harry Malone

The oil stone is such a simple thing that one is liable to neglect it and not give it the attention which it should have, and yet for the patternmaker it fills a very important place.

Until within a few years, all of the oil stones used were of the natural stone variety. Among the different stones found and used for sharpening tools, only two have ever found very extended use in this country. These are the Arkansas and the Waukesha. Both of these are fairly fine grained stones, of which silica is the principal ingredient. The prime requisite of any cutting stone is that it shall be composed of small angular particles of the cutting material, which are bound or cemented together with a suitable bond. This bond must be of such a strength that it will hold the particles until they have done a considerable amount of cutting and have become quite dull. When the particles have become dull enough to exert considerable resistance to the object being cut, the bond should give away and allow them to pass off with the material ground from the tool and this removal of the particles would expose fresh surface or cutting edges.

The object of oil or water on an oil stone is two-fold. First, it is used to remove the material cut from the tool in being sharpened; and second, for the removal of the particles worn from the stone. From this it is evident that the oil or other fluid used on the oil stone must be of such a nature that it will carry off these particles and that too without forming a gum which would smear and stop up the space between the cutting points. The trouble commonly known as glazing in an oil stone comes from the filling of the spaces between the cutting points, mainly with metal cut from the tool being ground, though the presence of some thick oils hastens the process greatly and the glazing material generally contains some of the particles ground or cut from the tool. To prevent glazing, a considerable amount of fluid must be used for carrying away the particles of steel and stone. The natural oil stones mentioned above possess especial ly fine cutting properties, coupled with an extremely fine grain, which fits them for fine work.

Natural stones, however, do not run uniform, and the stone beds are interlaced with small veins of quartz, which makes it impossible to obtain large stones clear from these quartz seams, and such seams injure the quality of the stone greatly.

The finer the oil stone, the greater care should be taken with it, and upon fine stones nothing but the best of oils should be used. Nothing will gum up an oil stone quicker than a thick, heavy machine oil. The best oils for the ordinary grades of oil stones are olive oil or sperm oil, the latter being preferable. Plenty of oil should be used and the surface wiped off frequently with a piece of waste or cloth. It must be remembered that the proper function of the oil is to carry away the cuttings and that this can not be done unless the oil itself is removed after it has become charged with the cuttings. Too many persons think that the oil is simply for a lubricant and seem to imagine that the material cut from the steel is going to evaporate in some mysterious way. If the bond of one of these oil stones is weak it sometimes overcomes all difficul:y it-self by breaking down readily under the heavy pressure necessary to overcome the partially glazed surface, and the necessary wiping of the tools with shavings or waste removes the oil and cuttings. But the best and highest grade oil stones do not break down as freely as this, and hence greater care should be taken with them. Frequently it is well to clean a stone which has become somewhat gummed up with gasoline or benzine. This will dissolve the oil and leave the stone with a fresh surface for work.

If the stone has become badly gummed with the heavy machine oil, it is necessary to soak the stone in a strong lye for several hours and then rinse it off in clean water and wipe it dry. The lye will cut the grease and serve to put the surface of the stone in better shape. In many shops where soda kettles are used, it is common practice for the men to dip their oil stones into the soda kettle to clean them.

If the surface of one of these natural oil stones becomes worn out of true it may be smoothed or trued up in any one of a number of ways. Small stones may be ground true very readily by applying them to one side of the grindstone. If no grindstone is at hand emery may be placed on a cast iron plate, water added, and the stone ground down by hand upon the iron surface. The plate should be planed true both to produce a true surface and to remove the scale so that the grains of emery can get a better grip on the iron.

A sheet of lead placed upon a true, flat surface, or a sheet of zinc may also be used to support the emery and water. If the stone is fairly soft, good sharp sand may sometimes be used in place of emery, but it will not cut it as fast. Where none of the above-mentioned metals are available, the emery and water are sometimes used on the surface of a smooth board. Sometimes an oil stone is dressed off by placing a sheet of sand paper or emery cloth upon a board, sprinkling it with emery, applying another coat of glue and another coat of emery, etc., until several coats have been applied and dried upon the surface. The oil stone may be very quickly trued upon the surface.

While all of the above named processes apply very well to natural oil stones, the artificial oil stones come under a very different class. There are three kinds of artificial oil stones now made. First, plain emery slips or blocks; second, Indian oil stones which are made from Indian corundum, and third, the carborundum oil stones. All of these are so hard that they cannot be ground or trued up on a grindstone. They may be trued, however, by using emery, corundum, or carborundum upon an iron plate or lap, as above described.

What has been said as to the use of oils on an oil stone applies equally well to the artificial stone, except that some of them will cut as well with water as they will with oil, providing plenty of water is used.

They say a good workman is known by his tools, but no good workman can keep his tools in good shape if he does not possess a good oil stone, and hence great care must be exercised to keep the oil stone in proper condition. No regular sharpening oil stone should be used without having a definite place to keep it, where it will be protected from the dust and dirt. For this purpose it is best to set the stone in a wooden block and provide a wooden cover for it. Some parties recommend the placing of a piece of hardwood, such as hickory, at each end of the stone and dressing it off level with the stone bo that the entire surface of the stone can be used without fear of damaging the point of the tool by dragging it back off from the edge of the stone, at with the piece of wood flush with the surface of the stone the tool would simply glide over it. Patternmaker.