6255. To File a Flat Surface

6255.    To File a Flat Surface. In filing a flat surface on a piece of iron, unless there is some skill or care used in the operation, the exterior edges are apt to bo greatly pared away, so that that part of tho surface about midway between them will bo the least filed down. The work should be held in a bench vise, in such a position that the file will run in a horizontal direction nearly level with the workman's elbow; but should the work bo of a very light nature, it may be held in a more elevated position; or, if it be very heavy, it may be held a little lower. In filing flat surfaces, a 'surface-plate' is used, to enable the operator to finish tho work with accuracy. Tho surface-plate is a cast-iron plate planed and carefully reduced to a true surface. Some red lead is rubbed on this plate before being used; then this piece of work is rubbed on the plate, and wherever the work is reddened it shows that that part of the work is above the level, and has to be filed down; and this process of testing and filing is carried on until tho work is reduced to a perfectly true surface. It saves the file to draw it back at each stroke as lightly as possible. There is also economy in using the files first on brass or cast iron, and afterwards on wrought iron.

6256. Recutting Files with Acids

6256.     Recutting Files with Acids. There are many receipts for converting old files into new by means of acids, and among the latest is that recently patented by Albert I. Ferguson, of Sharon, Pa. The files must bo thoroughly cleansed in warm water containing a small quantity of potash, which readily removes any grease or dirt from them. After the files are thus cleansed, they must bo washed with warm water and dried by artificial heat. Next, place 1 pint warm water into a wooden vessel, and put into it as many files as the water will cover. Then add 2 ounces blue vitriol (sulphate of copper) finely pulverized, and 2 ounces borax, well mixed, taking care to turn the files over, so that each may come in contact with tho mixture. To the above mixture now add 7 ounces sulphuric acid and 1/4 ounce cider vinegar, which will cause the files to assume a red appearance at first, but they will in a short time resume their natural color. Then they must be removed, washed in cold water, and dried by artificial heat. "When dry, they must be sponged with olive oil, wrapped in porous paper, and laid aside for use.

6257. Re-Sharpening Files

6257.    Re-Sharpening Files. A very interesting and economical process has been exhibited before the Société d'Encouragement of Paris, by M. Werdermann. Well-worn files are first carefully cleaned by means of hot water and soda; they are then placed in connection with the positive pole of a battery, in a bath composed of 40 parts sulphuric acid, 80 parts nitric acid, and 1000 parts water. The negative pole is formed of a copper spiral surrounding the files, but not touching them; the coil terminates in a wire which rises towards the surface. This arrangement is the result of practical experience. When the files have been 10 minutes in the bath they are taken out, washed, and dried, when the whole of the hollows will be found to have been attacked in a very sensible manner; but should the effect not be sufficient, they are replaced for the same period as before. Two operations are sometimes necessary, but rarely more. The files thus acted upon are, to all appearance, like new ones, and are said to be good for sixty hours' work.