Modern Machine-Shop Practice Part 150

[Ill.u.s.tration: Fig. 2213.]

[Ill.u.s.tration: Fig. 2214.]

[Ill.u.s.tration: Fig. 2215.]

[Ill.u.s.tration: Fig. 2216.]

[Ill.u.s.tration: Fig. 2217.]

Hand-files are tapered in thickness from their middle towards both the point and the tang, and are, therefore, well curved or bellied on each side. This fits them for the most accurate of work, on which account they are generally preferred by expert workmen. They are nearly parallel in width and have one safe edge and one edge cut single, while the face is cut double. Hand-files are also made equaling, the term equaling meaning that, although apparently blunt or of even thickness throughout the length, yet, in fact, there is a slight curvature, due to the file being thickest in the middle of its length. An equaling hand-file is especially suitable for such purposes as filing out long keyways, in which a great part of the file length is in action, and it can, therefore, be easily pushed in a straight line.

The flat file, Fig. 2213, when 10 inches and under in length, is made taper on both its sides and edges, from the middle to the front of the file, and when longer than 10 inches they should be made full taper--that is to say, the taper should extend from the middle toward the heel, as well as toward the point. Flat files are usually double-cut, the coa.r.s.e-cut being used upon leather, wood, and the soft metals. The flat b.a.s.t.a.r.d is that most commonly used, the flat second-cut, smooth, and dead-smooth being used by machinists for finishing purposes, the latter preceding the polishing processes.

Pillar files are tapered in thickness from the middle to each end; the width is nearly parallel, and one of the edges is left safe. They are double-cut, and, although not in general use, are especially adapted to narrow work, such as in making rifles, locks, &c. The square file ranges from 3 to 16 inches in length, and is made for general purposes with considerable taper. It is usually double-cut, the b.a.s.t.a.r.d being the princ.i.p.al cut, the second-cut and smooth being mainly used by the machinist.

Square blunt files range from 10 to 20 inches in length, of the same sectional sizes as the square taper, and are cut double, usually b.a.s.t.a.r.d. For machinists' use, however, they are used in the second-cut also, and are provided with sometimes one and sometimes two safe sides.

Square equalling files are in every respect like the square blunt, except in the care taken to prepare a slight curve or belly in the length of the file, which greatly enhances their value in filing out the edges of keyways, splines, or mortises. The fault of the square blunt, when used for fine, or true work, is that the heel, having no belly, is apt to come into too prominent action.

[Ill.u.s.tration: Fig. 2218.]

Warding files, Fig. 2218, are made parallel in thickness, but are considerably tapered on their edges. They range in size from 3 to 8 inches in length, progressing by half-inches in the sizes below 6 inches. They are cut double, and usually on both edges, and are mainly used by locksmiths and jewellers, and to but a limited extent by machinists. Some of the warding files are provided with teeth upon their edges only, which are made quite rounding, the cut usually being second-cut, single.

[Ill.u.s.tration: Fig. 2219.]

[Ill.u.s.tration: Fig. 2220.]

[Ill.u.s.tration: Fig. 2221.]

Files deriving their sections from the circle are shown from Figs. 2219 to 2222. "Round files" are circular in section, as shown in Fig. 2219, their lengths ranging from 2 to 16 inches, and are usually of considerable taper. The small b.a.s.t.a.r.ds are mostly single-cut and the larger sizes double-cut. The second-cuts and smooths are rarely double-cut, except in some of the very large sizes. In imitation of double-cut, however, they are sometimes made with the first, or overcut, very open, called "hopped," which adds, however, but very little to the cutting capacity of the file. The very small sizes--as, say, those of one-quarter inch and less in diameter--are often called "rat-tailed"

files. For some cla.s.ses of work--as for instance, the circular edges of deep keyways--round, blunt files are used, their sizes running up to 18 and 20 inches, their princ.i.p.al cut being b.a.s.t.a.r.d and double.

The gulleting file is a round, blunt saw file, and, like most other files for this purpose, is single-cut (except for a small s.p.a.ce at the point, which is left uncut). Its princ.i.p.al use is for extending the gullet of what are known as gullet-tooth and briar-toothed saws.

Half-round files are of the cross-section shown in Fig. 2220, and although their name implies a semicircle, yet, as generally made, their curvature does not exceed the third part of a circle. They are made taper; the b.a.s.t.a.r.d is usually double cut on both its sides; the second-cut and smooth is double-cut on their flat sides, and single-cut on the curve side, except occasionally in the larger sizes, when it is double-cut or hopped. Half-round files for wood usually range in size from 10 to 14 inches, and are of the same shape and taper as the regular half-rounds. They are cut coa.r.s.e and double, and are used by wood-workers generally. Half-round rasps are also like the regular half-round in shape, the sizes usually called for being 10, 12, and 14-inch. They are used princ.i.p.ally by wheelwrights and carriage builders, but are to some extent used by plumbers and marble workers.

[Ill.u.s.tration: Fig. 2222.]

Cabinet files are of the section shown in Fig. 2222, being both wider and thinner than the half-rounds, the sectional curvature being somewhat less than the fifth part of a circle. They are made taper from near the middle to the point, while both the files and the rasps are made from 6 to 14 inches in length; 8, 10, and 12 inches are the sizes in most common use. As usually known, the cabinet file is a b.a.s.t.a.r.d double-cut.

The cabinet rasp is punched smooth, and both the cabinet rasp and file are rarely made of any other degree of coa.r.s.eness. They are used by cabinet, saddle-tree, pattern, and shoe-last makers, and also by gunstockers and wood-workers generally.

[Ill.u.s.tration: Fig. 2223.]

Three-square files are made with equilateral triangular sections, as in Fig. 2223. They are tapered to a small point with considerable curve, and are double-cut. The larger sizes--say, from 10 to 14 inches--are usually b.a.s.t.a.r.d, and are used to a considerable extent in rolling mills.

The smaller sizes are not unfrequently smooth or dead-smooth, and are used in machine shops quite generally for filing interval angles more acute than the rectangle, clearing out square corners, sharpening cutters, &c. Three-square blued files of sizes from 3 to 6 inches are sometimes made. They are mostly second-cut, or smooth and double-cut, and are princ.i.p.ally used in machine shops for filing up cutters for working metals.

[Ill.u.s.tration: Fig. 2224.]

[Ill.u.s.tration: Fig. 2225.]

Cant files, whose cross-sections are shown in Fig. 2224, are usually made blunt and double-cut, mostly b.a.s.t.a.r.d, on all three sides. These sizes are usually 6, 8, and 10 inches. Lightning files are of the cross-section shown in Fig. 2225, the term lightning being known princ.i.p.ally by those using the saws of this name, and to some extent by those using other cross-cut, [M]-shaped saw teeth. The obtuse angle of this file is five-canted, while the regular cant is hexagon or six-canted, and it is found to be too obtuse for the purposes required of the saw file. They are made blunt, and range in length from 4 to 12 inches, and are cut (except for a short s.p.a.ce near the point) single on their three sides.

[Ill.u.s.tration: Fig. 2226.]

[Ill.u.s.tration: Fig. 2227.]

[Ill.u.s.tration: Fig. 2228.]

Knife files are of the section shown in Fig. 2226, and rarely exceed 10 inches in length, the princ.i.p.al sizes being 4, 5, and 6-inch. They are tapered, resembling somewhat the blade of a knife, and are cut double.

The very acute angle of the sides of this file makes it especially useful in filing the inner angles of the rear and main springs of a rifle lock and work of similar shape. These files are also made blunt.

Cross files (sometimes called double half-round or crossing files) are of the section shown in Fig. 2227. They are mostly made to order, either blunt or tapered, and usually double-cut. "Feather-edge" files (Fig.

2227) are but little used by the mechanics of this day. They were formerly used in filing feather springs (as the rear spring of a gun lock is sometimes called), and also the niches in currycombs, which led them to be called by some currycomb files. The few files of this kind which are now made are usually blunt and double-cut. Half-round "shoe rasps" as generally made are of the cross-section shown in Fig. 2228, their sizes ranging from 6 to 12 inches, while 8, 9, and 10 inch are the most common. They are made parallel in width, but with their sides slightly tapered from the middle; the ends are rounded and cut single; the edges are safe or uncut, or if cut are usually made half-file and half-rasp reversed (1/4 rasp and 3/4 file, while sometimes made, are the exception). The file quarters are b.a.s.t.a.r.d double-cut, and the rasp quarters second-cut. This form of shoe rasp is the one in general use at this time, having almost entirely superseded the flat and swaged rasps formerly in use.

[Ill.u.s.tration: Fig. 2229.]

Reaper files (B, Fig. 2229), so called from their use in sharpening the knives of reaping and mowing machines, are of the cross-section shown.

They range in length from 7 to 10 inches, are slightly tapered, and are cut single and on their sides only.

Tumbler files, whose cross-section is shown at A, Fig. 2229, were formerly much used to file the tumblers of gun locks, but are now rarely called for. They are taper and cut double. It will be seen, however, that unless for some special purpose, the pitsaw round or half-round file will be found to answer the same purpose as the tumbler file.

It is obvious that in the use of files the coa.r.s.er cuts are for use when it is required to remove a maximum quant.i.ty of material, and the finer to produce a more smooth and true surface, and also that the form of file selected is that which will best conform to the shape of the work, or can be best admitted upon or into the work.

In selecting the length of the file, the size of the work and the delicacy of the same are the determining considerations; thus, a 14-inch file would be a clumsy tool upon a small piece of work, as, say, one having an area of 1/2 inch square. In selecting the shape of the file there are, however, other considerations than the shape of the work.

Among these considerations may be enumerated that, in proportion as the number of teeth on any given file, performing cutting duty simultaneously, is increased, the less metal will be taken off, because the pressure on each tooth is reduced, and the file does not bite or take hold of the work so well; hence it cuts smoother.

To fit the handles to small files, as 6-inch or less, it is simply necessary to bore suitable-sized holes in the handles, and force in the tang of the file. In doing this care should be taken to bore the hole axially true with the handle, so that the latter may stand true with the file, which greatly a.s.sists the production of true and rapid filing.

For larger files the handle should have a small hole bored up it as before, the file tang should be made red hot (a piece of wet rag or cotton waste being wrapped around the heel of the file, so that it shall not get hot and be softened), and forced into the handle by hand, the file and handle being rotated during the operation, and sighted to insure that the handle is kept true with the centre line of the file. So soon as the tang of the file has entered three-quarters or thereabouts of its length it should be removed and gradually cooled by dipping in water.

[Ill.u.s.tration: Fig. 2230.]

[Ill.u.s.tration: Fig. 2231.]

When the surface of the work is so large that the file handle would meet the work before the point had reached fully across it, the raised handle shown in Fig. 2230 is employed. The square end of the handle has a dovetail groove into which the tang of the file is fitted. In the figure the file is shown applied to a connecting rod end, and in such broad surfaces it is especially necessary to vary the line of motion of the file after every few strokes, so as to cause the file marks to cross and recross, as shown in Fig. 2231.

The height at which work should be held to file it to the best advantage depends entirely upon its size, the amount of metal to be filed off, and the precision to which the filing requires to be executed.

Under ordinary conditions the work should stand about level with the operator's elbow when he stands in position to file the work. This is desirable so that the joint of the arm from the elbow to the wrist may be in the same plane as the line of motion of the file, which will give the workman the least fatigue. But when the work surface is very broad it should be lower down, so that the operator may reach over all parts of its surface. On the other hand, on very small round work, or work so small as to require but one hand to hold the file, the work may be so high as to require the operator to stoop but very little, in which case the fatigue will be less, while the work will be more in sight, and can be better scrutinized.

[Ill.u.s.tration: Fig. 2232.]

When the file is pushed endways it is termed cross-filing, and the teeth cut on the forward or pushing stroke only, and in this case the file should be held as in Fig. 2232, the end of the file handle ab.u.t.ting against the palm of the right hand. But when the file is held in one hand only, the forefinger may be placed uppermost, and either on the file handle or on the file itself, as may be found most convenient. In cross-filing the file should be relieved of cutting duty on the return or back stroke, but should not be removed from the work surface.

For heavy cross-filing on iron or bra.s.s, a 15-inch file is sufficiently large for any of the ordinary duty required by the machinist, and will require all the pressure one man can put on it to enable it to cut freely, and move at a suitable speed.

The workman should for heavy cross-filing stand well off or away from the work so as to require to bend the body well forward. His feet should in this case be spread apart so that when the pressure of the hands is placed upon the file it will relieve the forward foot of a great part of the weight of the workman's body, which will be thrown upon the file.

The rear foot operates during the forward stroke as a fulcrum, wherefrom to push the file.

At each forward stroke the workman's body should move somewhat in unison with the file; his arms being less extended than would otherwise be the case, and the file being under more pressure and better control.