Machinery's Handbook, 31st Edition
1052 Files and Burs File Characteristics.— Files are classified according to their shape or cross section and according to the pitch or spacing of their teeth and the nature of the cut. Cross Section and Outline: The cross section may be quadrangular, circular, triangular, or some special shape. The outline or contour may be tapered or blunt. In the former, the point is more or less reduced in width and thickness by a gradually narrowing section that extends for one-half to two-thirds of the length. In the latter the cross section remains uniform from tang to point. Cut: The character of the teeth is designated as single, double, rasp or curved. The single- cut file (or float as the coarser cuts are sometimes called) has a single series of parallel teeth extending across the face of the file at an angle of from 45 to 85 degrees with the axis of the file. This angle depends upon the form of the file and the nature of the work for which it is intended. The single-cut file is customarily used with a light pressure to produce a smooth finish. The double-cut file has a multiplicity of small pointed teeth inclining toward the point of the file arranged in two series of diagonal rows that cross each other. For general work, the angle of the first series of rows is from 40 to 45 degrees and of the second from 70 to 80 degrees. For double-cut finishing files, the first series has an angle of about 30 degrees, and the second from 80 to 87 degrees. The second, or upcut, is almost always deeper than the first or overcut. Double-cut files are usually employed, under heavier pressure, for fast metal removal and where a rougher finish is permissible. The rasp is formed by raising a series of individual rounded teeth from the surface of the file blank with a sharp, narrow, punch-like cutting tool and is used with a relatively heavy pressure on soft substances for fast removal of material. The curved-tooth file has teeth that are in the form of parallel arcs extending across the face of the file, the middle portion of each arc being closest to the point of the file. The teeth are usually single cut and are relatively coarse. They may be formed by steel displacement but are more commonly formed by milling. With reference to coarseness of cut, the terms coarse, bastard, second and smooth cuts are used, the coarse or bastard files for the heavier classes of work and the second- or smooth-cut files for the finishing or more exacting work. These degrees of coarseness are only comparable when files of the same length are compared, as the number of teeth per inch of length decreases as the length of the file increases. The number of teeth per inch varies considerably for different sizes and shapes and for files of different makes. The coarseness range for the curved-tooth files is given as standard, fine and smooth. In the case of Swiss pattern files, a series of numbers is used to designate coarseness instead of names; Nos. 00, 0, 1, 2, 3, 4 and 6 being the most common with No. 00 the coarsest and No. 6 the finest. Classes of Files.— There are five main classes of files: mill or saw files; machinists’ files; curved-tooth files; Swiss pattern files; and rasps. The first two classes are commonly re- ferred to as American pattern files. Mill or Saw Files: These are used for sharpening mill or circular saws, and large crosscut saws; for lathe work; for draw filing; for filing brass and bronze; and for smooth filing generally. The number identifying the following files refers to the illustration in Fig. 1. 1) Cantsaw files have an obtuse isosceles triangular section, a blunt outline, are single cut and are used for sharpening saws having M-shaped teeth and teeth of less than 60-degree angle; 2) Crosscut files have a narrow triangular section with the short side rounded and a blunt outline, are single cut and are used to sharpen crosscut saws. The rounded portion is used to deepen the gullets of saw teeth, and the sides are used to sharpen the teeth themselves; 3) Double ender files have a triangular section, are tapered from the middle to both ends, are tangless and single cut, and are used reversibly for sharpening saws; 4) The mill file itself is usually single cut, tapered in width, and often has two square cutting edges in addition to the cutting sides. Either or both edges may be rounded, how- ever, for filing the gullets of saw teeth. The blunt mill file has a uniform rectangular cross section from tip to tang; 5) The triangular saw files or taper saw files have an equilateral
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