GONEOMETER.
All the eccentric tools require the greatest care in sharpening, and the above ingenious machine has been invented for this purpose; it is represented at P, in [plate 4]. The upper part, 1, is a plate of brass, the outer edge, 2, is graduated as high as 50 each way, beginning at the tongue, 3. Beyond the numbers is a groove, in which one end of the tool slide, 4, slips, and is firmly fixed (so as to point to any of the numbers that suit the angle of the tool) by a nut underneath. The whole plate, 1, is raised and lowered at pleasure by a small hinge at 5, and the requisite height is fixed and settled by counting the numbers on the steel tongue, 3. Underneath is another brass bed with two feet, upon which the machine rests, while the front part leans forwards and rests upon the end, 5. The box that contains the goneometer has three drawers in it; the first is lined with brass, except for about three inches in width, which space is covered with fine Turkey stone. To use this machine, take out this drawer, lay the feet of the goneometer on the brass, put the slide-rest tool, No. 4, into the tool box, screw it firm, then slide the tool box along the groove till it arrives at the proper angle, say 45; fix it with the nut underneath, then raise the whole brass plate, 1, sliding it along the tongue, 3, till at the exact height necessary for the tool to touch the Turkey stone. Rub it backwards and forwards upon it with oil. When one side is sharp, move the tool slide to the opposite angle, to sharpen the other. The small eccentric tools are placed in the steel case, U, and the case fits into the tool slide.