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Files, Rasps and their Makers

  Sharpening Files - Engineering, an Illustrated Weekly Journal, London, 1878  

Mr. B. C. Tilghman has recently discovered another and very interesting application of the sand blast to industrial purposes. He has found that by subjecting worn files to the action of the jet, the cutting edges are rapidly renewed, and the file is made sharper than when new.

The process is as follows: A stream of fine sand impelled at a high velocity by a jet of steam is applied to a file in the manner shown in the sketch, Fig. 1, at an angle of from 10 deg. to 15 deg. from its face; the file being moved about so that all parts may be acted on. The sand for the purpose is very fine grit prepared by washing and settling. It is used in the state of very soft slime drawn from a receiver, as shown in the sketch.

The effect upon the teeth of a file which has become dull by wear, is to grind away some of the metal from the inclined Bides of the teeth Bo as to reproduce a cutting edge, as shown by Fig. 2.

In this sketch the lines a a show the flat surfaces produced by wear on the points of the teeth; the dotted lines b b show the new surfaces produced by the grinding action of the sand, and the new cutting edges produced where this surface meets the vertical sides of the teeth.

The bottom diagram, Fig. 3, shows the action of the blast on a new file. In this case it removes the burr on each tooth, bringing it to a much sharper edge.

A comparative trial of the cutting power of the sharpened files was lately made with the following results: A piece of soft wrought iron was filed clean and weighed; 1200 strokes were made by a skilled workman with one side of a new 10 in. bastard file, the iron was again weighed, and the loss noted.

The other side of this file was then subjected to the sand blast for five seconds, and 1200 strokes were made with this sand-blasted side on the same piece of iron, great care being taken to give strokes of equal length and pressure in both cases. The iron was then weighed, and the loss found to be double as much as in the first case.

These operations were repeated many times, counting the strokes and weighing the metal each time, and the quantity cut was found to gradually become less for both sides as these became worn.

When the weight of metal cut away by 1200 strokes of the sand-blasted side was found to be no greater than had been cut by the first 1200 strokes of the ordinary side when quite new, a second sand blasting was applied to it for 10 seconds, and in the next 1200 strokes its rate of cutting rose to nearly its first figure.


When the cut made by the ordinary side of the file fell to about four-tenths of its cut when new, it was considered by the workman as worn out, and a new file of the same size and maker was used to continue the comparison with the one sand-blasted side; 83 sets of 1200 strokes each, and 13 sand blastings were made on the same side of this file, and in that time it cut as much metal as six ordinary sides. In 99,600 strokes it cut away 14 oz. avoirdupois of wrought iron, and 16.4 oz. of steel.

With an equal number of strokes its average rate of cutting was, on wrought iron, 50 per cent, greater than the average of the ordinary sides, and on steel 20 per cent, greater. As the teeth became more worn, the time of the application of the sand blast was lengthened up to one minute. After the thirteenth re-sharpening its rate of cutting was nine-tenths that of the ordinary aide when quite new.

When the teeth become so much worn that the sand blast ceases to sharpen them effectively, the file can be re-cut in the usual way, and each set of teeth can be made to do six times as much work as an ordinary file, and to do it with less time and labour, because it is done with edges constantly kept sharp.

The time required to sharpen a worn out 14-in. bastard file is about four minutes, or proportionately less if sharpened before being entirely worn out. Smooth files require much less time. About 4 horse power of 60 lb. steam used during four minutes, and one pint per minute of sand (passed through a No. 120 sieve), and the time of a boy are the elements of cost of the operation.

Engineering, an Illustrated Weekly Journal, London, 07/28/1878


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