9 70000 700 ooo ooko ooto 121212 333 333 333 44 121212 333 HHHH 121212 12 12 12 4444 100 100 100 100 NOTE.half the pitch in practice it is necessary to make the thread a little more than half in order to allow clearance for the screw that goes into the threaded hole. The amount of this clearance depends on the character of the work and varies from .001 inch up. Some also make the tap so that the screw will only bear on the top or bottom and the sides. While in theory the thread and the space are both one FILES FILES are designated both by the spacing of their teeth and the shape or cross-section of steel on which the teeth are cut; the size always referring to their length which is measured from the point cutting to the end of the file proper but the measurement never includes the tang which fits into the handle. TERMS USED The back of a file is the convex or rounding side of half-round, cabinet and other files having a similar shape. A file is Bellied when it is full or large in the center. A Blunt file is the same size its whole length instead of being tapered. An Equalling file is one which looks blunt but which has a slight belly or curve from joint to tang. A Float file is a coarse single cut made for use on soft metals or wood and frequently used by plumbers. A Safe-edge is an edge left smooth or blank so that the file will not cut if it strikes against the side of a slot or similar work. The Tang is the small pointed end forged down for fitting into the handle. Three square files are double cut and have teeth only on the sides, while taper saw files are usually single cut and have teeth on the edge as well as the sides. This makes the taper saw files broad on the edge or without sharp corners, while the three square files have very sharp corners. A special angle tooth file is made for brass work. The first cut is square across the file, while the second is at quite an acute angle, about 60 degrees from the first cut. Doctor files are very similar to these except that the first cut is about 15 degrees instead of being square across the file. A lock file has safe edge and the teeth only go about one third the way across from each side leaving the center blank. The teeth are single cut. HIGHT OF WORK The work should be at a convenient hight which will usually vary from 40 to 44 inches for most men with an average of 42 inches. This means the hight of the work, not the bench. PICKLING BATH A good pickle to soften and loosen the scale on cast iron before filing is made of two or three parts of water to one part of sulphuric acid. Immerse castings for a short time. For brass castings use a pickle of five parts water to one part nitric acid. THE TEETH OF FILES The cut of a file or the number of teeth per inch vary with the length of the file itself and the kind of a file, and is a little confusing, as rough cut in a small file may be as fine as a second cut of a larger size. The cuts used on regular 12-inch files are shown in the illustration and represents the practice of Henry Disston & Sons. The same makers also supply the table of cuts per inch used on their machines, which are as follows: REGULAR TAPER FILES · 21, 3, 31, 4, 41, 5, 51, 6, 61, 7, 8, 9, 10, MILL FILE, BASTARD CUT Length - 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20 in. Teeth 56, 50, 48, 46, 44, 42, 40, 38, 36, 34, 32, 30, 28, 26, 24, 22 per inch. FLAT FILE, BASTARD CUT 48, 42, 38, 36, 32, 30, 26, 24, 22, 20, 20, 18, 18, 16, 16, 14. Single cut files usually have teeth at about 25 degrees and in double cut files the other cut is usually from 45 to 50 degrees. machinists files are made in ten numbers from oo to 8. THE SHAPES OF FILES Fine In the following pages the shapes of standard files are shown. The names are as follows: single line of cuts across the surface, at an angle with the file body but parallel to each other. The double-cut file has two lines of cuts, at an angle with each other, and the second cut being usually finer than the first. Some prefer the single cut, for filing in the lathe. Rasps have single teeth forced up with a punch. The old method of designating the cuts were rough, coarse, bastard, second cut, smooth and dead smooth. Some makers are now using a series of numbers - usually eight to ten - instead of the six designations by name formerly employed. The uses of the various cuts depend on the shop in question and must be learned from observation and experience in each case. The grades of cut used by them run from No oo to No. 8, and while it is hard to exactly compare them with the old-style designations, it will be found that No. oo is about the same as a bastard, No. 1 as a second cut, No. 2 or 3 with a smooth, and Nos. 6 to 8 with a dead smooth file. |