Modern Machine-Shop Practice Part 159

In cases where the bra.s.ses are difficult to get out of the strap, because of the location or of the size and weight of the parts, a piece of sheet bra.s.s is sometimes placed between the joint faces, and this piece is filed thinner to let the bra.s.ses together, the necessary thickness for the piece being ascertained by the lead wire process described. If the strap is held to the rod end by a gib and key only, and the joint faces are left open, there is nothing to lock the strap to the rod end save the jaws of the gib, whereas when the bra.s.ses b.u.t.t, the key binds the bra.s.ses to the end face of the rod and the strap to the bra.s.ses, which if there is any wear sideways (as in locomotives), prevents the keys from wearing the sides of the key ways and the bra.s.s f.l.a.n.g.es from wearing the straps.

A method of overcoming this defect is shown in Fig. 2379, where the joint faces are left open, and four set-screws S, S, two on each side of the rod, pa.s.s through the f.l.a.n.g.e of one bra.s.s and abut against the face of the other, serving to adjust the fit of the bra.s.ses to the journal, and lock them in their adjusted position, locking at the same time the bra.s.ses to the strap and the strap to the rod end.

When the rods are finished so far as the fitting of its various parts are concerned, the bra.s.ses should be marked so that the bore, when bored out, will leave an equal thickness of metal between the bra.s.s and the strap on each side of the bore, while the rod will be of proper length.

To accomplish this, mark on the outside face of the top bra.s.s two lines level with the faces which fit against the inside jaws of the strap, as shown in Fig. 2380, A, B being the lines referred to. We then key up the bra.s.ses in their places in the rod and fasten a centre piece in the bra.s.ses at each end of the rod. Upon these centre pieces we first mark a line parallel with and central between the lines A, B, and then a line across the joint of the bra.s.ses if the joint faces meet, and in the centre of the s.p.a.ce between them if they do not meet.

[Ill.u.s.tration: Fig. 2379.]

[Ill.u.s.tration: Fig. 2380.]

Before applying the trammels to test the rod length, the latter should be stood or placed in the position in which it works when on the engine; for all rods deflect by their weight, the amount of such deflection depending upon the position in which the rod is suspended. The trammels also deflect, it is true, but their deflection is allowed for in setting them, whereas the deflection of the rod will not be accounted for unless it is trammelled when standing or lying in the position in which it works.

FITTING UP SOLID-ENDED CONNECTING RODS.--In fitting up solid-ended rods the side faces require to be filed up first and the jaws to receive the bra.s.ses next, taking care to file them out either square with the faces, or if slightly taper, as they should be, then each inside face should be an equal degree of taper to the side faces. This is necessary so that if the bra.s.ses are bored true to their own faces, the bore of the bra.s.ses at one end of the rod shall stand parallel to the bore of those at the other end.

The fitting of the keys and bra.s.ses is performed as described for strap-ended rods.

The reason that the jaws or box that receives the bra.s.ses is but a trifle taper is that in that case they are easier made a good fit, as they can be tried in their places while being fitted and before being reduced to the finished size, and furthermore because they can be put in and taken out easier.

FITTING UP A FORK-END CONNECTING ROD.--A fork-end connecting rod affords as good an example of vice work as can be found, because any faulty workmanship, either in the individual truth of the parts, or their relative truth one part to another, will make itself very plainly apparent.

[Ill.u.s.tration: Fig. 2381.]

[Ill.u.s.tration: Fig. 2382.]

Fig. 2381 represents a side and plan view of an ordinary form of fork-end rod, and the requirements are that the centre line A of the bra.s.s bores at the fork end shall be parallel with the centre line B of the bore at the b.u.t.t end; that the side faces of all the bra.s.ses shall be parallel one to the other; that the side faces at the fork end shall be equidistant, or at the required distance, from the side faces at the b.u.t.t end as denoted by C, D; that the bores of the bra.s.ses shall be at the proper distance apart to make the length of the rod come right; that the bra.s.ses at the fork end shall be the right distance apart, and that they shall stand parallel to each other, as well as to the bore at the b.u.t.t end, as denoted by the line E in Fig. 2382.

If the rod were of a size that it could be conveniently handled and planed, if forged solid, the fitting up would be much simplified, because the setting of the rod for the machine operation would, to a great extent, insure truth in the relative alignment of the parts. Thus all the side faces of the rod ends could be planed at one chucking, in which case they would necessarily be parallel, and their proper relative distances apart, if the rod was properly marked out by lines and planed to the lines. The jaws or ways to receive the bra.s.ses would be slotted out together, and necessarily true, if the rod was chucked true on the machine table. But even in this case the rod has to be marked out by lines denoting where the metal is to be cut off to, and the principles involved in the lining are just the same as those involved in the fitting up.

[Ill.u.s.tration: Fig. 2383.]

[Ill.u.s.tration: Fig. 2384.]

If the rod be large, the ends may be, and usually are, forged and fitted up separately, and subsequently welded to the body of the rod, which has been forged separately. In this case, the alignment of the parts is a part of the process in welding the rod, and setting it after welding.

All the principles involved in making the rod ends separate, and afterwards welding them, or in marking out a small and complete forged rod, are, however, involved in the process of refitting an old rod in the jaws, and putting in new bra.s.ses; hence a description of that process will cover the whole ground. The first thing to do is to file up the side faces, as F, G, Fig. 2381, and, in doing this, all that is necessary is to file F up true, when tested by a straight-edge applied as in Fig. 2383, in which R is the fork and S a straight-edge, whose edge should measure the same distance at H as it does at I from the side face F, while the face C measures the same distance from face A of the other fork end, or from the imaginary centre line X, Fig. 2381. Then turning the rod on its side, a straight-edge should be placed across the face F, and one across the face G, as in Fig. 2384, at S and S'; and the edges of the two straight-edges should stand parallel, when sighted in such a position that the edges are very nearly in line with the eye, as shown in the figure.

The inside faces of the fork jaws may be filed to measurement from the outside ones.

[Ill.u.s.tration: Fig. 2385.]

[Ill.u.s.tration: Fig. 2386.]

[Ill.u.s.tration: Fig. 2387.]

The ways for the bra.s.ses should be filed square with the outside faces, as shown in Fig. 2385, in which S is a [T]-square; but if one jaw is wider than the other, as sometimes occurs, it will not matter, providing that, with the square applied, resting against the side and the face of the ways on the narrow jaw, the ways of the other jaw are equidistant from the square blade, as would be the case; for example, if the width of the ways of the jaw J extended to the dotted lines at K, L, because the line P would still form the centre line of both jaws, standing at a right angle to the side faces of the fork end, and parallel to the bore of the bra.s.ses at the b.u.t.t end. Before filing up the side faces at the b.u.t.t end, the strap should be fitted on and keyed up, so that its side faces may be filed up with those on the rod. To test the truth of the side faces at the b.u.t.t end, a straight-edge should be applied, as at S and S", Fig. 2386, being pressed firmly to the side faces at the b.u.t.t B, the fork faces being measured from the edge of the straight-edge at that end, and also with straight-edges, as in Fig. 2384. The bra.s.ses, after being fitted into the ways of the jaws, should have their joint faces squared, as in Fig. 2387, the top of each jaw being shown broken away, so as to fully expose the bra.s.ses. S is a square held firmly against the side face of a jaw, the bra.s.ses having their joint faces true with the square blade, and true also when tested with a square, applied as in Fig. 2388, in which B is the bra.s.s and S the square. The bra.s.ses at the other end should be filed true to the side faces of the strap in a similar manner, and, the fitting being completed, it simply remains to mark off the bra.s.ses for boring. The joint faces of the bra.s.ses should form the centre of their respective bores; hence, all that is necessary, is to insure that the bra.s.ses be of equal thickness, top and bottom, and this may be accomplished as follows: Mark across each face a line even with the ways of the bra.s.s, as shown in Fig. 2389, at A, C, and carry these lines around the side face, as shown in the figure at B, D. Place the bra.s.ses in the strap, put in a piece of wood whereon the compa.s.ses may be rested, as shown in Fig. 2390, which represents one jaw, and mark on this piece of wood a line even with the joint faces of the bra.s.ses, and on this line a centre-punch dot equidistant between the lines B, D. From this dot, as a centre, strike the circle shown, and define it by centre-punch dots, and if the lathe-hand chucks the bra.s.ses true to the ways that fit the rod jaws, and to the dotted circle, the bores will stand true in every respect.

[Ill.u.s.tration: Fig. 2388.]

[Ill.u.s.tration: Fig. 2389.]

[Ill.u.s.tration: Fig. 2390.]

REPAIRING CONNECTING RODS.--In repairing connecting rods the following is the work usually required to be done, and in the order named: Refitting straps, refitting gibs, and perhaps new gibs and keys, filing up the side faces of rod ends and straps, lining up bra.s.ses to make them fit the strap, lining up the rod to length and fitting the bra.s.ses together so as to fit their journals.

[Ill.u.s.tration: Fig. 2391.]

If the strap is taper and can be closed by pening, the outside of the back should be pened; but if the strap requires closing in the blacksmith's shop, then it should be tested by winding strips as shown in Fig. 2391, to insure that the faces are true, and thus save filing at the key ways and on the side faces to make them come fair with the rod ends. The rod ends should then be filed up and the straps fitted on.

[Ill.u.s.tration: Fig. 2392.]

[Ill.u.s.tration: Fig. 2393.]

[Ill.u.s.tration: Fig. 2394.]

Next comes putting in the new key and gib, or refitting the old gib. If the jaw of the gib has cut into the strap, as it will do in some cases (especially in marine and locomotive rods), this may be repaired as follows: Cut out the recess shown in Fig. 2392 at A, making it dovetail-shaped as shown, and with a set chisel set up its sides as shown in Fig. 2393, which is a sectional side elevation through the line of B. Cut out a piece of wrought iron and bevel its edges as shown in Fig. 2394, filing it to fit into the recess cut at A, Fig. 2392, and letting the bevelled edge be uppermost. Then take a set chisel and close down again upon the bevelled edge of the piece the metal that was set up, as shown in Fig. 2393, and the piece will be riveted, and it and the gib jaw may be refitted to touch the piece thus let in.

[Ill.u.s.tration: Fig. 2395.]

The jaws of the gib are sometimes made slightly taper at A, Fig. 2395.

To refit the bra.s.ses to the jaws of the strap, the f.l.a.n.g.es which do not as a rule wear much are usually tinned with a soldering iron, and given a lining of babbitt metal. This must be done all around the f.l.a.n.g.es (of both pairs of bra.s.ses) that come on the same side of the rod, so as to keep the faces of the bra.s.ses leading fair.

[Ill.u.s.tration: Fig. 2396.]

The fit between the jaws is restored by riveting pieces of sheet bra.s.s to that side of the bra.s.ses that has worn the most (usually the top which carries the weight of the rod). Fig. 2396 shows this operation carried out, A being the pieces of sheet bra.s.s which are sometimes soldered as well as held by rivets. These rivets are screwed into the bra.s.s, being composed of softened bra.s.s wire riveted after being screwed in.

If these pieces, which are called liners, are placed on the top of the bra.s.ses at one end, they should also be placed at the top of the bra.s.ses at the other end of the rod. They should not be less than about the 1/24 inch thick, the body of the bra.s.s being cut off to admit them if necessary.

In filing the joint faces of the bra.s.ses to let them together so as to take up the lost motion due to the wear of the bra.s.s bore and of the crank pin, the following considerations are met.

[Ill.u.s.tration: Fig. 2397.]

If the bra.s.s faces are to come "bra.s.s and bra.s.s," that is, b.u.t.t together, when their bore is of the diameter of the journal, file those faces away until the bore appears just perceptibly too large for the journal, when measured with calipers, as in Fig. 2397, the bore measuring parallel all the way through. But, in doing this, it is necessary to be careful to file each bra.s.s so that it shall embrace one-half the journal diameter, which will be the case when the two bra.s.ses measure correctly as above, and alike, when tested, as in Fig.

2398, in which P is a planed surface, C a pair of inside calipers, and B a bra.s.s resting on P. When filing the joint faces, test them with a square as in Fig. 2399, in which _s_ is a square and B a bra.s.s, and also in Fig. 2400, in which _s_ is a square and B the bra.s.s shown in section, thus making the faces quite square.

[Ill.u.s.tration: Fig. 2398.]

[Ill.u.s.tration: Fig. 2399.]

[Ill.u.s.tration: Fig. 2400.]

The necessity of having their faces quite square when the bra.s.ses come bra.s.s and bra.s.s may be shown as follows:--

[Ill.u.s.tration: Fig. 2401.]

Suppose the joint to be at an angle as at A, A, Fig. 2401, instead of square across, as denoted by the dotted lines B, B, then the respective bra.s.ses will be forced by the key-pressure in the direction of the respective arrows, and there will be a tendency to twist the bra.s.ses in the strap. Or suppose the joint faces to be out of square as at C, C, instead of square as at D, then there will be a tendency to twist the respective bra.s.ses in the direction of E, F, and therefore to cause these to move in the direction of G, H, and as a result the bra.s.ses will spring the strap away from the rod, as shown at I, J.

[Ill.u.s.tration: Fig. 2402.]