71/79 58, cuts even more quickly than the natural stones. It is made in several grades of coarseness. The medium grade is recommended for ordinary shop use. Oil is used on oilstones for the same purpose as water on a grindstone. When an oilstone becomes hollow or uneven by use, it may be trued by rubbing it on a flat board covered with sharp sand, or on sandpaper tacked over a block of wood. |