In a double-cut file, the thousands of points or teeth occur from two series of straight chisel-cuts crossing each other; in a single-cut file or float, the ridges occur from the one series of chisel-cuts, which are generally square across the float; and in a rasp the detached teeth are made by solitary indentations of a pointed chisel or punch, a subject that will be further noticed when the cutting of files is adverted to.
Double-cut files are made of several gradations of coarseness, and which are thus respectively named by the Lancashire and Sheffield makers: -
The sizes marked with asterisks are not commonly made, and this reduces each scale of variety of cut to four kinds, of which the Lancashire are somewhat the finer. The above names afford, however, but an indifferent judgment of the actual degrees of coarseness, which, for all the denominations of coarseness, differ with every change of length; but the numbers in the annexed table may be considered as pretty near the truth: -
Approximate Numbers of Cuts in the Inch of Lancashire Files*
Lengths in Inches.
Of floats and rasps, but two denominations are generally made, and which are simply distinguished as coarse and fine; the fine are also called cabinet floats and rasps; and as with the files, the two nominal sizes of the teeth of floats and rasps, differ for every variety of length in the instruments.
* The numbers in the Table, were counted from the engravings of the teeth of files in Mr. Stubs' pattern book. These engravings were laid down with great care from the files themselves, and it is somewhat curious the numbers should so nearly fall in regular series. The second courses of teeth were in each case counted, and which are somewhat finer than the first course, as explained on page 829.
One of the smallest and finest Lancashire files, was found by the author to contain from 290 to 300 cuts in the inch, which is confirmatory of the above numbers.
5. Safe-edges. - Some files have one or more edges that are left uncut and these are known as safe-edge*, because such edges are not liable to act upon those parts of the work against which they are allowed to rub, for the purpose of guiding the instrument. The safe-edge file is principally required in making a set-off, or shoulder, at any precise spot in the work, and in filing out rect-angular corners; as whilst the one side of the notch is being filed, the other side can be used to direct the file. Occasionally the edges alone of files are cut, and the sides are left safe or smooth, as in some warding files, which nearly resemble saws.
6. The names of files. - These are often derived from their purposes, as in saw files, slitting, warding, and cotter files; the names of others from their sections, as square, round and half round files.
Figs. 805. Sections derived from the Square.
Figs. 806. Sections derived from the Circle.
Figs. 807. Sections derived from the Triangle.
Files of all the sections represented in the groups, figs. 805, 806, and 807, are more or less employed, although many of them are almost restricted to particular purposes, and more especially to the art of watchmaking, for which art indeed, very many of the files have been originated. The sections may be considered to be derived from the square, the circle, and the equilateral triangle, as will be detected by the eye without description.
To avoid wearying the reader by attempting to describe all the various files that are made, the eight or nine kinds which are of most extensive application, will be briefly adverted to, and these will be placed in the supposed order of their usefulness as derived partly from the author's observation, and partly from the relative quantities considered to be manufactured of each kind in two large establishments. After this, a few remarks will be given on some of the files to which the sections 805 to 807 refer, and this, or the first division of the chapter, will be concluded by a short account of the mode of forming the teeth of files, and some other particulars of their construction.
It may be considered that in nearly every branch of art in which the file is used, that the following constitute the basis of the supply; namely, taper files, hand files, cotter and pillar files, half-round, triangular, cross, and round files, square, equalling, knife and slitting files, and rubbers; a short explanation will be given of all of these varieties, in the course of which, reference will be occasionally made to the sections A to Z just given.
Taper files, or taper flat files, are made of various lengths from about 4 to 24 inches, and are rectangular in section as in B fig. 805; they are considerably rounded on their edges, and a little also in their thickness; their greatest section being towards the middle of their length or a little nearer to the handle, whence these files are technically known to be "bellied;" they are cut both on their faces and edges with teeth of four varieties, namely, rough, bastard, second-cut, and smooth-cut teeth. Taper flat files are in extremely general use amongst smiths and mechanics, for a great variety of ordinary works.
Hand files or flat files resemble the above in length, section, and teeth, but the hand files are nearly parallel in width, and somewhat less taper in thickness than the foregoing. Some few of them are called parallel-hand-files, from having a nearer equality of thickness, and parallelism of sides. Engineers, machinists, mathematical instrument makers and others, give the preference to the hand file for flat surfaces and most other works, except in filing narrow apertures and notches, as then the small end of the taper file, first described, may be employed in the commencement, gradually the central and wider part, and then the entire length of the instrument, as the space or notch to be filed becomes wider; the taper form thus enables a larger and stronger file to be used in the commencement, but for other and accurate purposes the hand file is esteemed preferable to the taper.