44 Laboratory Arts 



be remembered that there is a great tendency to " rock " the 

 file when at work, and this should be watched for and avoided. 

 Also, the roughness or coarseness of a file should be suited 

 to the material it has to work. Fine files cut hard materials 

 best, and should never be used upon lead, solder or similar 

 substances. 



Files may be cleaned and kept in fair working order with 

 a little care. Cleaning may be done by means of a " scratch 

 brush " consisting of a membrane pierced with 

 many steel wires, such as is used in the preparation 

 of various fibres in textile industries. Should this 

 fail to remove the "dross" choking the teeth, it 

 may be removed by the action of strong nitric acid 

 (for removing brass, tin, solder, etc.) or dilute 

 sulphuric acid (for removing iron), the file being 

 afterwards well washed in hot water, dipped for 

 a few moments in methylated spirit, which is then 

 set on fire. The file by this means is cleaned and 

 dried. 



A new type of file is now being placed on the 

 market, known as the " Dreadnought " milling file 

 (Fig. 34). The teeth are portions of a circle, and 

 are machine cut. They may be re-sharpened several 

 times at small cost, and the files act in a " positive " 

 manner, cutting and not scratching the metal away. 

 Probably these will presently take the place of the 

 old files altogether, as they have many advantages, 

 one important one being that they cut all metals 

 equally well, without clogging, consequently may be 

 DreacT used for solder, lead, brass or iron indiscriminately. 

 "n" gh fii' Another great advantage is that they leave the 



muling file. , ... 



surface ready for finishing or scraping, neither the 

 fine file nor " draw filing " being necessary. These files are 

 somewhat expensive, but as they save other files, as well as 

 time, their first cost is soon repaid. 



Stocks, Dies, and Taps. These should be of Whitworth 

 Standard. Several very convenient sets of tools are now 

 upon the market. One such set is the " Duplex " adjustable 



