One who has given the matter careful attention, and has built file-testing machines, Edward G. Herbert, of Manchester, England, has come to the conlcusion that a file does not cut best when it is new but after it has been used for some little time, say 2500 strokes or the filing away of one cubic inch of metal. Another curious feature is that its usefulness seems to come to a sudden instead of a gradual end. A bastard file having 25 teeth to the inch, operating on a surface one inch square with a pressure of 30 pounds, which is about equal to heavy hand filing, gives 25 cutting edges about one inch long, which likens it somewhat to a broad cutting tool in a planer. In cutting a file the metal is forced up in a sort of a bur, and occasionally the top of the tooth slopes over backward which is the reason that a file often cuts better after these are broken or worn off. Then, too, when a file is new all the teeth are not of the same hight and only a few points cut. As they wear down more teeth come into contact and do more work. WORK BENCHES THE duties of a bench vary with the shop in which it is located according to the work that is to be done on it or at it. If it is simply a filing bench, the main requirement is that it support a vise firmly and at the proper hight. If an assembling bench, these are not the important features, and just what it does need depends on the kind of work being handled. For the average shop work we want a bench that is rigid; that will stand chipping and filing; that can be used in testing work on a surface plate or in handling jigs and fixtures; that will not splinter badly nor yet injure a tool should it happen to drop on it. For the toolmaker the cast-iron bench top has many advantages, but both the bench and the tool are very liable to be marred by dropping the tool on it, so that for general use we rely on wood as in the days of old, except that a bench with solid 2- or 3-inch planking the whole width is now too expensive to consider. We no longer want the bench braced up against the side of the shop but set it out from B FIG. 1. Good for Ordinary Work. FIG. 2. Another Method. the wall to allow the heat to rise and the air to circulate, as well as giving the sprinklers a chance to get at a fire on the floor near the walls. The use of a lighter board at the back has become so common that the New Britain Machine Company's design for a bench leg is made for this construction as shown in Fig. 1. This also shows the backboard B rabbeted to the plank A, which supports it all along the front edge, and it is also supported by the stringer D, which runs the whole length of the bench. These supports, in addition to the cross bearing of the legs every 6 or 8 feet, give the backboard a stiffness that was unknown where they are simply laid flush and not rabbeted and the stringer is absent. Benches made without these supports are open to the serious objection that the backboard springs down when a heavy weight, such as a jig or surface plate, is put on the bench and throws them out of level. All cracks are more or less of a nuisance in bench work, but in this case any shrinkage can be taken up by wedging against the iron support of the board C and the edge of the backboard B. |