The tangs are now softened to prevent their fracture; this is done either by grasping the tang in a pair of heated tongs, or by means of a bath of lead contained in an iron vessel with a perforated cover, through the holes in which, the tangs are immersed in the melted lead that is heated to the proper degree; the tang is afterwards cooled in oil, and when the file has been wiped, and the teeth brushed clean, it is considered fit for use.

The superiority of the file will be found to depend on four points, - the primary excellence of the steel - the proper forging and annealing without excess of heat - the correct formation of the teeth - and the success of the hardening. These several processes are commonly fulfilled by distinct classes of workpeople, who are again subdivided according to the sizes of the files, the largest of these being cut by powerful muscular men, the smallest by women and girls, who thereby severally attain great excellence in their respective shares of the work.

The manufacture of files, especially the cutting of the teeth, has been entered into much more largely than was at first intended, but it is hoped this may not be without its use; as notwithstanding the suitability of ordinary files to most purposes, still occasions may and do occur, in which the general mechanist or amateur may find some want unsupplied, which these hints may enable him to provide for, although less perfectly, than if the file in question had been manufactured in the usual course. The process of cutting teeth, is also called for in roughing the jaws of vices and clamping apparatus.*

Means of grasping the file. - In general the end of the file is forged simply into a taper tang or spike, for the purpose of fixing it in its wooden handle, but wide files require that the tang should be reduced in width, either as in fig. 813 or 814. The former mode, especially in large files, is apt to cripple the steel and dispose the tang to break off, after which the file is nearly useless; the curvilinear tang, 814, is far less open to this objection, and was registered by Messrs. Johnson, Cammell, and Co., of Sheffield. Some workmen make the tangs of large files red hot, that they may burn their own recesses in the handles, but this is objectionable, as the charred wood is apt to crumble away and release the file: it is more proper to form the cavity in the handle, with coarse floats made for the purpose.

* There is perhaps an equal mixture of philosophy and prejudice in the hardening of files: some attach very great importance to the coating or defence, others to the medication of the water, and all to the mode of immersion best calculated for each different file, in order to keep it as straight as possible, questions of opinion which it is impossible to generalise. Mr. Stubs's process of manufacture is pretty much as above described, and although he has experimented with mercury at 8o F., as the cooling medium, as well as various fluids, he has arrived at the conclusion, that the salt principally acts at an antiseptic, and that fresh spring water at 45* is as effective as any fluid.

In driving large files into their handles, it is usual to place the point of the file in the hollow behind the chaps of the tail vice, and to drive on the handle with a mallet or hammer. Smaller files are fixed obliquely in the jaws of the vice, between clamps of sheet brass, to prevent the teeth either of the vice or file, from being injured, and the handle is then driven on. The file, if small, is sometimes merely fixed in a cork, or in a small piece of hazle rod, but these are to be viewed as temporary expedients, and inferior to the usual wooden handles turned in the lathe. Very small watch files are fixed in handles no larger than drawing pencils, and some few of them are roughened on the tang, after the manner of a float, and fixed in by sealing wax or shell lac.

Files Section I General And Descriptive View Of Pi 200217

Several of the small files have the handles forged in the solid, that is, the tang is made longer than usual, and is either parallel, or spread out, to serve for the handle, as in a razor strop; many of the watch files are thus made. In the double-ended rifflers, or bent files, fig. 815, used by sculptors and carvers, and in some other files, there is a plain part in the middle, fulfilling the office of a handle; and in several of the files and rasps made for dentists, farriers, and shoemakers, the tool is also double, but without any intermediate plain part, so that the one end serves as the handle for the other.

In general the length of the file exceeds that of the object filed, but in filing large surfaces it becomes occasionally necessary to attach cranked handles to the large files or rubbers, as in fig. 816, in order to raise the hand above the plane of the work. Sometimes the end of the file is limply inclined, as in fig. 817, or bent at right angles, as in 818, for the attachment of the wooden handles represented; but the last two modes prevent the second side of the file from being used, until the tang is bent the reverse way. The necessity for bending the file is avoided by employing as a handle, a piece of round iron 5/8 or 3/4 inch in diameter, bent into the semicircular form as an arch, the one extremity (or abutment), of which is filed with a taper groove to fit the tang of the file, whilst the opposite end is flat, and rests upon the teeth; in this manner, both sides of the file may be used without any preparation.

Fig. 819 represents, in profile, a broad and short rasp with fine teeth, used by iron-founders in smoothing off loam moulds for iron castings, this is mostly used on large surfaces, to which the ordinary handle would he inapplicable, and the same kind of tool when made with coarser teeth, will be recognised as the baker's rasp. For some slight purposes, ordinary files are used upon large surfaces, without handles of any kind, the edges of the file itself being then grasped with the fingers.