MECHANICAL AND USEFUL ARTS. 69 



one of the simplest description. It consists in driving a chisel of suit- 

 able form and inclination to a small depth into the prepared surface 

 of the blank, and steadily withdrawing it again ; and cutting a file 

 is merely a repetition of this operation. The difficulties to be sur- 

 mounted are — to present the blank perfectly parallel to the cutting 

 edge of the chisel ; to withdraw the chisel from the incision made 

 in the blank without damaging the edge of the newly-raised tooth ; 

 to prevent a rebound of the chisel after the blow which drives it 

 into the blank, and before the next blow is struck ; to give a uniform 

 traversing motion to the blank, ensuring regularity in the teeth ; to 

 proportion the intensity of the blow to the varying width of the file, 

 so as to give a uniform depth of cut ; and to perform these operations 

 at such a speed as to make them commercially profitable. In most of 

 the attempts that have been made to accomplish this process by ma- 

 chinery, the idea has been to construct an iron arm and hand to 

 hold the chisel, and an iron hammer to strike the blow ; and by this 

 means to imitate as nearly as possible the operation of cutting by 

 hand. The difference in the material used inevitably led to failure : 

 the flexible and to some extent non-elastic nature of the fingers, 

 wrist and arm, enabled the man to hold the chisel, strike the blow, 

 and then lift the chisel from the tooth, without vibration : not so 

 when the iron hand and hammer are tried to perform the same ope- 

 ration ; the vibration consequent upon the material employed fre- 

 quently caused irregularity in the work and a ragged and uneven 

 edge on the tooth. The slow speed at which these machines were 

 •worked rendered them unable to compete with hand labour. 



In the machine forming the subject of the present paper the above 

 objections have been nearly, if not altogether, obviated by an inge- 

 nious modification in the mode of action. This machine is the in- 

 vention of M. Bernot, of Paris, and has been already working suc- 

 cessfully for some time both in France and Belgium. The blow is 

 given by the pressure of a flat steel spring pressing upon the top 

 of a vertical slide, at the lower end of which the chisel is firmly 

 fixed ; the slide is actuated by a cam making about one thousand 

 revolutions per minute, and the chisel consequently strikes that num- 

 ber of blows per minute, thus obviating the vibration consequent upon 

 the blow with an iron-mounted hammer, and moving at such a speed 

 as to render any vibration impossible. 



In the files cut by this machine the teeth are raised with perfect 

 regularity, and consequently when the file is used each tooth per- 

 forms its proper share of work ; whereas, in hand cutting, from the 

 varying power of the muscles, especially towards the close of the 

 day, it is impossible to produce such perfectly uniform work. 



A manufactory employing twelve of these machines has been esta- 

 blished at Douai, in the north of France, and another at Brussels, 

 in both of which the machines have been in successful operation for 

 nearly two years. 



In a discussion which followed the reading of the paper, Mr. 

 Greenwood stated that there was no difficulty in cutting round files 

 in the machine as well as flat files ; the machines were of smaller 

 size for this purpose, working at a speed as high as 1500 strokes per 



