The-next process is the preparation of the surfacfor the teeth of the files. This, when it is done by means of filing, as practised in Lancashire, is called stripping. At Shef field, the surface of the file has no other preparation for cutting than by grinding. This is done by machinery, and at a trifling expense.
The great expedition with which the grinding of files is performed, and the little attention paid by the workman, who is totally unacquainted with every other department, cannot insure that evenness of surface which is of so much importance in the working of a file, and which is more suc cessfully performed by stripping.
The grinding-stone would require constant examination to keep it sufficiently true for grinding an even surface, except some additional machinery could be employed for that purpose. This will doubtless be some time or other accomplished. 0 In the present state of the file manufacture, the larger files must be prepared on the present plan, and must re main imperfect for want of the surface being even. If this is not the case before the file is cut, it will, on using, be found to touch the surface to be filed only in a few points, instead of the whole of the teeth touching at once. It is in this particular that the Lancashire files have so much surpassed those made at Sheffield and Birmingham. The first are prepared solely by stripping ; and, in consequence, their trade is confined to the small cast-steel files, for which they easily get a price double that of similar Sheffield files. When the manufacturers of the latter are told that it is in this particular that they arc defective, it seems wonderful that they do not either adopt some process analogous to stripping, or contrive some machinery to grind them more exactly.
The stones used at present for grinding files, are of •sharp gritstone, and of considerable size, for the large files, from four to five feet in diameter. They wear them down to about 30 inches, and then sell them to the fork-grinders. The grinder sits so as to lean over the stone, which turns directly from him, and presses on the file with both hands. The files are now transmitted to the cutter. The expedi tion and exactness with which the teeth of files are cut, is not surpassed by any mechanical art, depending like it solely upon human dexterity.
The file cutter requires an anvil of a size great or less, proportioned to the size of his files, with a face as even and flat as possible. The hammers are from one to five or six pounds. His chissels are a little broader than the file, sharpened to an angle of about 20 degrees. The length is sufficient to be held fast between the finger and thumb, and of strength sufficient not to bend with the strokes of the hammer, the magnitude of which may be best con ceived by the depth of the impression. The anvil is placed in the face of a strong wooden post, to which a wooden seat is attached a small distance below the level of the anvil's face. The file is first laid on the bare anvii, lane end pro. jetting over the front, and the other over the back edge of the same. A leather strap now goes over each end of the file, and passes down on each side the block to the work man's feet, which, being put into the strap on each side, like a stirrup, holds the file firmly upon the anvil, while it is cut. While the point of the tile is cutting, the strap passes over one part of the file only, while the point rests upon the anvil, and the tang upon a prop on the other side of the strap. When one side of the file is single cut, a fine file is run slightly over the teeth, to take away the roughness, when they arc to be double cut, and another set of teeth are cut, crossing the forMernearly at right an gles. The file is now finished on one side, and it is evi dent that the cut side cannot be laid upon the bare anvil to cut the other. A flat piece of an alloy of lead and tin is interposed between the toothed surface and the anvil, while the other side is cut, which completely preserves the side already cut. Similar pieces of lead and tin, with angular and rounded grooves, are used for cutting three-square and half-round files.
.11asps are cut precisely in the satire way, using a trian gular punch instead of a flat chissel. The great art in cutting a rasp is, to place every new tooth opposite to a vacancy as much as possible.