FILE 367 



which screw stops against the under side of an ear projecting from the framework, 

 and thereby determines the extent of the motion of the lever r, when depressed _by 

 the tappets of the wheel s, acting upon the inclined plane t, consequently determining 

 the number of teeth the ratchet wheel p shall be moved round by the pall q ; and 

 hence the extent of motion communicated by the rack and pinion to the slide /, and 

 the blank j, which regulates the distance that the teeth of the file are apart, and the 

 lover r is forced upwards by a spring pressing against its under side. 



It will be perceived that the velocity of the descent of the hammer, and conse- 

 quently the force of the blow, may be regulated by raising or lowering the inclined 

 plane v of the spring u ; and in order to accommodate the bed upon which the blanks 

 rest to the different inclinations they may be placed at, the part of the bed is formed 

 of a semi-globular piece of hardened steel, which fits loosely into a similar concavity 

 in the bed r, and is therefore capable of adjusting itself, so that the blanks shall be 

 properly presented to the cutting tool, and receive the blow or cut in an equal and 

 even manner ; or the piece of steel may be of a conical shape, and fit loosely in a 

 similar shaped concavity. 



There are guides 16, placed on the top of the bed i, for the purpose of keeping the 

 blanks in their proper position towards the cutting tool, and these can be regulated 

 to suit blanks of any width, by turning the right and left handed screw 17- ^ There is 

 also another adjustable stop on the jaws or clamps k which serves as a guide when 

 placing the blanks within the jaws : and 19 is a handle or lever for raising the clamps 

 when required, which has a weight suspended from it for the purpose of keeping down 

 the blanks with sufficient pressure upon the bed. 



The cutting tool in the face of the hammer can be placed at any required angle or 

 inclination with the blank, it being secured in the head of the hammer by clamps and 

 screws. In cutting fine files a screw is employed in preference to the rack and pinion, 

 for advancing the slide I, and the blank piece of steel in the machine. 



Hardening the Files. This is the last and most important part of file-making. 

 Whatever may be the quality of the steel, or however excellent the workmanship, if 

 it is not well hardened all the labour is lost. 



Three things are strictly to be observed in hardening : first, to prepare the file on 

 the surface, so as to prevent it from being oxidised by the atmosphere when the 

 file is red-hot, which effect would not only take off the sharpness of the tooth, but 

 render the whole surface so rough that the file would, in a little time, become 

 clogged with the substance it had to work. Secondly, the heat ought to be very 

 uniformly red throughout, and the water in which it is quenched, fresh and cold, 

 for the purpose of giving it the proper degree of hardness. Lastly, the manner of 

 immersion is of great importance, to prevent the files from warping, which in long 

 thin files is very difficult. 



The first object is accomplished by laying a substance upon the file, which, when 

 it fuses, forms, as it were, a varnish upon the surface, defending the metal from the 

 action of the oxygen of the air. Formerly the process consisted in first coating the 

 surface of the file with ale grounds, and then covering it over with pulverised common 

 salt (chloride of sodium). After this coating became dry, the files were heated red-hot, 

 and hardened ; after this, the surface was lightly brushed over with the dust of cokes, 

 when it appears white and metallic, as if it had not been heated. This process has 

 been improved, at least so far as relates to the economy of the salt, which from 

 the quantity used, and the increased thickness, had become a serious object. Those 

 who used the improved method are now consuming about one-fourth the quantity of 

 salt used in the old method. The process consists in dissolving the salt in water 

 to saturation, which is about three pounds to the gallon, and stiffening it with ale- 

 grounds, or with the cheapest kind of flour, such as that of beans, to about the con- 

 sistence of thick cream. The files required to be dipped only into this substance, and 

 immediately heated and hardened. The grounds or the flour are of no other use 

 than to give the mass consistence, and by that means to allow a larger quantity of 

 salt to be laid upon the surface. In this method, the salt forms immediately a firm 

 coating. As soon as the water is evaporated, the whole of it becomes fused upon the 

 file. In the old method the dry salt was so loosely attached to the file, that the 

 greatest part of it was rubbed off into the fire, and was sublimed up the chimney, 

 without producing any effect. 



The carbonaceous matter of the ale-grounds is supposed to have some effect in giving 

 hardness to the file, by combining with the steel, and rendering it more highly 

 carbonated. It will be found, however, upon experiment, that vegetable carbon does 

 not combine with iron, with sufficient facility to produce any effect, in the short space 

 of time a file is heating for the purpose of hardening. Some file makers are in the 

 .habit of using the coal of burnt leather, which doubtless produces some effect ; but 

 the carbon is generally so ill prepared for the purpose, and the time of its operation 



