Modern Machine-Shop Practice Part 156

For cutting out long narrow keyways, that are too narrow to admit of a machine cutting tool, and for very true holes, not to be cut out in quant.i.ties all of the same dimensions, it has no equal.

[Ill.u.s.tration: Fig. 2312.]

Hand drifts are sometimes used to cut keyways in small bores, as in small hubs, the method being shown in Fig. 2312, in which A represents a pulley with a keyway to be cut in the hub _b_; _c_ is a plug, and _d_ slips of iron placed between _c_ and the drift _e_ to press the latter to its cut. It is obvious that in this case the keyway in the pulley will be cut parallel, and the taper must be provided for in the key seat in the shaft. Keyways cut in this way are more true than those filed out. It is also obvious that the sides of the keyway, as well as its depth, may be finished by a drift, and this is very desirable (on account of insuring parallelism) when the key is to act as a feather that is to have contact on the sides and not bind top and bottom.

The most improved form and method of using this cla.s.s of tool, however, is as follows:--If a keyway is to be cut out of solid metal, holes are drilled as closely together as the length of the keyway will admit, their diameter nearly equaling the required width of keyway, after these holes are drilled through the metal remaining between them.

TEMPLATES.--Templates for vice work are used for two purposes: first to serve as guides in filing work to shape and size, and secondly to test the finished work. When used as guides to file the work they are mainly used to work of irregular, curved, or angular form, to which the square and other ordinary vice tools cannot be applied.

Fig. 2313 represents a template for filing out a square hole. The edges A, B are at a right angle to each other, the wire simply serving as a handle.

There are two methods of applying this template; the first is to file out two opposite surfaces of the hole to the required diameter, making them true and parallel one to the other, and to then employ the template while filing out the remaining two sides; the other is to file out one side and apply the template from that as a base for the other sides. The first is preferable because the liability to error is a minimum.

When work is to be from a template, the latter obviously becomes the original standard, and in many cases the best method of forming it so as to insure correctness and enable its proper application to the work is a matter of great consideration. The shape of the template must, of course, be marked by lines which should be as fine and as deep as possible. But it does not matter how closely the template may be filed to these lines, it will still have some error, and this can in many cases be discovered and corrected during its application to the work. In the following examples there are principles which will be found of general application:--

[Ill.u.s.tration: Fig. 2313.]

[Ill.u.s.tration: Fig. 2314.]

[Ill.u.s.tration: Fig. 2315.]

[Ill.u.s.tration: Fig. 2316.]

[Ill.u.s.tration: Fig. 2317.]

Let it be required to make or test a piece of work such as in Fig. 2314, the teeth to be equally s.p.a.ced, of the same angle, and of equal height.

A template must be made of one of the two forms shown in Fig. 2315. To begin with, take a piece of sheet metal equal in width to at least two teeth, and, a.s.suming that the template is to have two teeth, file its sides P Q, in Fig. 2316, parallel, and make the width equal to twice the pitch of the teeth. We next divide its width into four equal parts by lines, and mark the height, as shown in Fig. 2316. If we desire to make the template such as at A, we cut out the shaded portion; or for the template at B, the shaded portion. It will be observed, however, that in template A there are two corners C and D to be filed out, while at B there is but one E, the latter being the easier to make, since the corners are the most difficult to file and keep true. The best method of producing such a corner is to grind the teeth off the convex side and at the edge of a half-round file, producing a sharper corner than the teeth possess, while giving at the same time a safe edge on the rounded side that will not cut one angle while the other is being filed. But when we come to apply these templates to the work, we shall find that A is the better of the two, because we can apply the square S, Fig. 2317, to the outside of the template, and also to the edge F of the work, which cannot be done to the edges G of the work and H of the template, because the template edge overhangs. We can, however, apply a square S' to the other edge of B, but this is not so convenient unless the tops of the teeth are level.

[Ill.u.s.tration: Fig. 2318.]

[Ill.u.s.tration: Fig. 2319.]

a.s.suming, therefore, that the template A is the one to be made, we proceed to test its accuracy, bearing in mind that for this purpose the same method is to be employed whatever shape the template may be.

Consequently, we make from the male template A, Fig. 2318, a female template K, beginning at one end of K and filing it to fit A until the edges of A and K are in line when tested by a straight-edge S. We then move the template A one tooth to the right, and file another tooth in K, and proceed in this way until a number of teeth have been made, applying a square as at S, Fig. 2319, to see that the template A is kept upright upon K. When K has been thus provided with several teeth that would fit A in any position in which the latter may be placed, we must turn template A around upon K to test the equality of the angles. Thus, suppose at the first filing the edges _a_, _b_, _c_, _d_, upon A accurately fit the template K, and the straight-edge shows the edges fair; then if we simply turn the template A around, its angles, which were before on the right, will now be on the left, as is shown at the right of Fig. 2318. Thus in one position _a_ fits to _e_, in the other it fits to _h_, or _b_ fits to _f_, and when turned around it fits to _g_, and so on. Supposing that when thus turned around the angles do not coincide, then half the error will be in the teeth of A and one-half in those of K, and the best plan will be to correct them on A to the necessary amount as near as judgment will dictate, and then to apply K as before, continuing this process until A will fit anywhere in K, and may be turned around without showing any error. But at each correction the straight-edge must be applied, and finally should be tried to prove if the teeth tops are level. We thus have two interchangeable templates, of which A may be used on the work and K kept to correct A when the latter becomes worn. It may be as well to add, however, that in first applying A to K it is best to press the straight-edge S against the edge of K, and hold it there, and then to place A against S, and slide it down into K.

[Ill.u.s.tration: Fig. 2320.]

[Ill.u.s.tration: Fig. 2321.]

Fig. 2320 represents an example in which, the form being a curve, it would be best to have the template touch more than two teeth, as shown in the cut. By letting the side A, Fig. 2321, of the template T terminate at the centre line of the two curves, and the end B terminate at the top of a curve, turning the template around would cause end A to envelop side C of the middle curve, thus increasing the scope of the template. Suppose, however, that the base curve D required to be true with the teeth, then a second template T' must be used, its ends at E and F measuring an equal length or height, so that when they are placed even with the ends of the work, the distances G H being equal, the corrugations will be true to the curve D D. Now let it be supposed that, instead of making a template to test a piece of work such as in Fig.

2321, it is required to make a template for use in making another piece of work that is to fit to piece W, then template T in Fig. 2321 will not answer, because it is a female template, whereas a male one is required, so that the edge of the template may coincide with that of the work. But we may convert T, Fig. 2321, into a male template by simply cutting off the edge A as far as the line J, and causing its right-hand edge to coincide with the edge of the work so that the latter, after being fitted to the template, may be turned upside down and fit upon the piece of work.

[Ill.u.s.tration: Fig. 2322.]

[Ill.u.s.tration: Fig. 2323.]

[Ill.u.s.tration: Fig. 2324.]

In Fig. 2323 is an example in which the forms of both sides of a piece require to be exactly alike, and the easiest method of accomplishing this is as follows:--The face A should first be made true, and face B made parallel to A. A centre line C may then be drawn, and from it the lines E, E may be marked. The lines D are then drawn parallel to A A, lines E being made square to D and to A. The sides E may be calipered to width and parallelism, and all that will then remain is to file the angles F, F and the ends G, G to their required lengths. For F, F all that is necessary is a template formed as in Fig. 2324. The object of dressing the ends G, G last is that if they were finished before, their faces E would have to be made at exactly correct distances from them, which would render the job considerably more difficult.

[Ill.u.s.tration: Fig. 2325.]

[Ill.u.s.tration: Fig. 2326.]

Fig. 2325 represents a sketch for a piece of work whose two sides are to be shaped exactly alike, requiring a template of the form of the work, as shown. From this a second template, Fig. 2326, is made, and to this latter the work may be filed. To make the template in Fig. 2325, which represents the work, the edge _x_ _x_ must be made straight, and the edge D parallel to it at the proper height. A centre line S is then marked, and the edges at E may be filed equidistant from S and square to D; hence they will be parallel to each other. The side sections F should then be filed equidistant from S and parallel to each other. They should be the proper width apart and square to D, being tested in each of these respects. The line joining E and F should be left full, as denoted by the dotted line at A on the right. The edges at C, C should then be filed, calipering them from the edge _x_ _x_. Edges G, G are obviously equidistant from S and parallel to S, or, what is the same thing, at a right angle to _x_ _x_, from which they may therefore be tested with a square, and, finally, the edges B are made parallel to _x_ _x_, and the ends H made square to _x_ and equidistant from S. We have now to file the angular groove at A, and to get this true after marking its depth from the lines at A, we file it first to the lines as near as may be by the eye and very nearly to the full depth. We then make a small supplemental male template T, Fig. 2327, equal in width to the distance E F, or, in other words, to the width of the step at A, and having its edges quite parallel. Its end is then filed to fit the groove at A, when its edge meets and coincides with edge E, as in Fig. 2327, T representing the supplemental template. It is clear that when the [V]-groove A is so filed that T will fit it with either of its edges against E, the angles of the groove will be alike, and we may then make a male gauge, as in Fig. 2326, that may be used to mark or line out the work and to use as a template to file it to, its edge H being kept parallel to face D, Fig. 2325, of the work.

[Ill.u.s.tration: Fig. 2327.]

CHAPTER XXVII.--VICE WORK--(_Continued_).

[Ill.u.s.tration: Fig. 2328.]

[Ill.u.s.tration: Fig. 2329.]

There are two princ.i.p.al kinds of connecting rods, first those in which the bra.s.ses fit in s.p.a.ces provided in the solid rod, and which are known as solid-ended connecting rods, and second those in which the bra.s.ses fit in a strap secured by bolts or keys to the end of the rod. In Fig.

2328 is shown the simplest form of solid-end connecting rod. It consists of a rod enlarged at its end to receive a bra.s.s held up to the journal by a set-screw as shown, one-half the bore being provided in the rod and one-half in the bra.s.s. The objection to this kind of rod is that as the bore wears the rod gets shorter and no means is provided to restore its length, and that during the pulling stroke of the rod the whole of the strain is concentrated on the end area of the set-screw, and this causes it to imbed in the bra.s.s, giving play to the bra.s.s unless frequent adjustment is made. It is, therefore, difficult to readily maintain a very accurate adjustment of fit with a simple set-screw of this kind.

This may be to some extent remedied by the construction shown in Fig.

2329 in which the half bra.s.s A threads upon the stem of the rod, so that when it wears shorter to the amount of half the pitch of the thread upon the rod end, the bra.s.s may be unscrewed half a turn, and the original length will be restored. The cap is held on by two screws, which may have slotted heads as shown, or screws with check-nuts to prevent the screws from slackening back, as all screws are apt to do that receive alternating strains in reverse directions.

[Ill.u.s.tration: Fig. 2330.]

[Ill.u.s.tration: Fig. 2331.]

[Ill.u.s.tration: Fig. 2332.]

[Ill.u.s.tration: Fig. 2333.]

Yet another simple form of solid-end connecting rod is shown in Fig.

2330, there being two bra.s.ses with a key on one side and a set-screw on the other. In this case, as soon as either bra.s.s is moved by the key it can fit the rod at the top and at the bottom only; hence there is but little to hold the bra.s.ses sideways in the rod, and furthermore the bra.s.ses are damaged from the key and the set-screw acting directly upon them, as will be explained with reference to strap-ended rods. In Fig.

2333 is shown a very substantial form of solid-ended rod, a sectional view being shown in Fig. 2331. The bottom or back bra.s.s A has a f.l.a.n.g.e, as shown in Figs. 2331 and 2332 at A, which secures it to the rod end at the back. The top or key bra.s.s B has the keyway partly sunk in it, and the key binds against one side as well as on the bottom of the keyway, and this draws that bra.s.s close down to the face of the rod, as shown in Fig. 2331.

In this as in all other connecting rods in which one edge of the key beds against the back of the bra.s.s, the taper for the key should be cut in the rod so that the edge which meets the bra.s.s will stand square across the opening for the bra.s.s; in this way the back of the bra.s.s will also stand square across, which is easier to mark off and cut, plane, and fit. If the taper for the key is cut on the bra.s.s, marking the latter and fitting it become more difficult, as it must be put in and out of its place to fit and bed the taper for the key edge, whereas, in the other case, it can be squared with a square while planing and fitting. As the bore of connecting-rod bra.s.ses wears, and the lost motion incident thereto is taken up (by driving in the key) the location of the bra.s.ses in the rod end is altered, making the rod longer or shorter according to the location of the key. But when this wear has been sufficient to let the key pa.s.s through the rod, slips of iron termed liners are inserted between the backs or bedding faces of the bra.s.ses and the end of the rod or crown of the strap, as the case may be. In putting in these liners the location of the bra.s.ses in the rod end may be adjusted so as to bring the bra.s.s back to its original position and restore the rod to its proper length, and in doing so the back bra.s.s, as distinguished from the key bra.s.s, is the one to be lined first.

[Ill.u.s.tration: Fig. 2333.]

[Ill.u.s.tration: Fig. 2334.]

In the rod ends shown in Figs. 2333 and 2334 the joint faces (that is the faces where the bra.s.ses meet) must be filed away to take up the wear, hence the rods get shorter. In Fig. 2333 the liner may be placed behind either bra.s.s, A or B, or behind both, the thickness of that behind A adjusting the length of the rod (which is always measured from centre to centre of the respective bra.s.s bores), while the thickness of that placed behind B would simply act to prevent the key from pa.s.sing so far through the keyway. To prevent as far as possible the wear from altering the length of the rod, the key at one end of the rod is placed outside the crank pin or at the outer end of the rod, as in Fig. 2333, while at the other end it is placed between the bra.s.ses and the stem of the rod, as in Fig. 2334. In this latter case the thickness of liner placed behind the key bra.s.s B (as the bra.s.s against which the key bears, or the bra.s.s next to the key, is always termed) would adjust the length of the rod, while the thickness of liner placed behind the back bra.s.s (as the other bra.s.s is termed) would be the one to adjust the distance the key would pa.s.s through the keyway.

[Ill.u.s.tration: Fig. 2335.]

In this form of rod end, as in many other solid-ended rods, the f.l.a.n.g.e or collar of the crank pin, if solid with the pin, requires to pa.s.s through the opening in the rod end which receives the bra.s.ses. This may be accomplished by making that opening large or wide enough to pa.s.s over the crank-pin collar (which will increase the width of the bra.s.ses, and hence that of the rod end); or else the crank-pin collar may have two flat places filed on it, as in the end view shown in Fig. 2335. The objection to this plan is that the rod can only be taken on and off in one position of the engine; that is, when the two flat places A and B, Fig. 2335, stand parallel with the length of the rod.

[Ill.u.s.tration: Fig. 2336.]