The Scientific American Supplement index for Vol. 84
SCIENTIfIC AMERICAN SUPPLEMENT No. 21 91 415 Manufacture of Files FOR many years files were made entirely by hand, and at the present time the best files are still made in the same way. The file may be called a metal-cutting or abrasion tool, and it removes the metal by means of a series of sharp-edged parallel ridges all i�clined at an angle of about 50 degrees to the axis of the tool. There are numerous types of file differing in fineness of cut. These are all divided into two broad classes
... "double cut" and "float cut," or a "single cut." The former have two rows of cutting edges equally inclined to the axis and the latter have only one. In preparing the files steel blanks are first forged from bars which have been previously sheared or rolled to the section require for the tool. The blank is, of course, of soft steel. It is held on the anvil by a strap which passes round the tang, and is held down by the foot of the operator. If the under side has been cut already or is not flat, it is pro tected from damage by interposing lead or pewter as a soft support. Then, using a chisel which is rather wider than the blank, the operator makes a series of cuts parallel to each other and at the proper angle. The hammer is chosen with great care to be of such a mass as to cause the burr from each cut to rise to the right height. The distance of one cut from the next is gaged by resting the inclined chisel against the last burr when cutting the next. By increasing the slope of the chisel the distance apart of the burr is increased and vice-versa. It is obvious that the greatest skill and practice is re quired to strike, the chisel with the right force, and to keep its inclination constant over many hundreds of cuts. The height of the burrs as well as their distance from each other governs the fineness or coarseness of the cut. In the ordinary double-cut flat file there are 6 degrees of fineness respectively, called rough, middle, bastard, second cut, smooth, and dead smooth. Float-cut files are made in rough, bastard, and smooth varieties. In making double-cut files the first series of cuts are smoothed over very slighlty before maKing the second series. Lancashire used to make the best files, and even now no place can compete with it for the finest files, such as watchmakers use. The author of a classic work on the manipulation' of metals, mentions a fine Lancashire file on which he counted 300 cuts to the inch.