The head of the gib should be chamfered as in Fig. 2370, so that it may be driven in and out to fit without raising burrs which would prevent it from passing into the keyway, and the key should be similarly chamfered and rounded in its width.

The width of the key and gib should be such as to just fill the key ways, leaving no draw when the key is down in the keyway so that its head is level with the head of the gib, as in Fig. 2371, a equaling the keyway width; and their edges should bed fairly one against the other, and against the edges of the keyway. The strap must then be keyed upon the rod, and the side faces of the rod and strap planed to thickness, placing a bolt and nut in the rod end in place of the brasses, so that the key may lock the strap and bind it in position. The rod end should be planed to thickness for the brasses and of equal thickness on each side of the keyway. The brasses should be planed after the rod end is planed to thickness. The width for the brasses should be measured while the strap is on the rod end, because the width between the jaws of the strap is greater when the strap is in place on the rod end than when it is off, because in order to make the strap jaws a tight fit to the rod end it is made narrower between the jaws than the width of the rod end, so that the jaws spring open when the strap is pushed on the rod end. The sizes for the brasses to be planed to will then be the width of the strap across its edge face, and the width of the strap between the jaws when it is on the rod; and for these sizes a wire gauge should be made; or an adjustable gauge may of course be set.

The method to be pursued in planing the brasses is an important consideration. It is most convenient to plane both the brasses together, by which means much time is saved. To obtain this end the brasses are sometimes cast together, as in Fig. 2372, and after planing and before boring are cut in two at the narrow section a. In this case the brasses are cast sufficiently wide from crown to crown as denoted by b to allow for the length cut away in separating them. In other practice the joint faces of the brasses are faced first and then soldered together for the planing; but very large brasses are planed separately. In either case the joint face of the brass should be made at a right angle to the faces of the brass that fit the strap.

The brasses should be fitted separately to the strap, and hence should, if joined, be separated, being cut in two in a shaper, if of the form shown in Fig. 2372, and split by driving a keen chisel between the corners of the joint faces, if the latter have been soldered. The back or crown brass, and not the key brass, should be fitted first. The corners of the ways, in the brass, for the strap should be eased just clear with the edge of a smooth half-round file, because otherwise they will rub down the sharp edges of the strap, and make the strap jaws appear to be a bad fit when on the rod. The brass should be driven in and out of the strap to fit, using a block of wood to strike on, otherwise the skin of the bore may become pened, and when the brasses are bored they will close in at the sides and become loose in the strap.

As a guide when fitting the bottom brass in the strap, place the strap on the rod as in Fig. 2373, and take the measure of the strap at a a, the strap overlapping the rod to admit the calipers or gauge. Each time the brass is driven in the strap to try the fit, the calipers so set should be tried in the strap (the brass being in the strap), as in the figure, and when the calipers very nearly touch the strap jaws, the strap with the back brass still in should be tried on the rod end, or in the case of a very heavy strap the caliper measurement minutely taken may be relied on to show that the brass does not spring the strap jaws too wide open. It is better, however, to leave the brasses a little too tight in the strap as they close slightly in the boring, becoming easier in the strap.

After the brass has been tried in the strap, and before it is filed again, it should be tried with a square, using a straight-edge also if the square back is too short to cross both faces of the brass. The method of testing is shown in Fig. 2374, in which b represents the brass, s the square, and t the straight-edge. The inside face of the flange should also be tried as in Fig. 2375, in which p represents the surface plate, s the square, and b the brass. This will insure that the brass face joint is square as it should be, and is further necessary because the bearing marks on the brass are not to be altogether relied upon.

In Fig. 2376, for example, the brass is shown in section in the strap, and the side a of the brass has a bearing against the jaw b of the strap, and hence would show marks of contact. The succeeding blows in driving the brass, however, may cause the brass to have contact on the side c with the jaw d; hence the bearing marks would show the brass to fit well when such was not the case. This may be detected by striking the brass on its joint face, and then measuring from e and from f to the end of the strap, and then striking the joint face at f and again measuring both distances, when any canting of the brass will readily be detected. It is better, however, to also apply the square, as shown in Figs. 2374 and 2375, because by this means the joint faces e f being parallel to the crown face g of the brass, the brass will be fitted so that when g meets the crown face h of the strap, the two will be parallel to each other and require but little filing to fit or bed together.

The crown of the brass should be bedded very finely to the strap, or it will spring the strap jaws away from the rod when the key is driven home.

Suppose, for example, that the crown of the brass did not bed well at a in Fig. 2377, then keying up the strap would spring its jaws away from the rod end, as shown at b c, the least error in the bedding having this effect notwithstanding the fit of the gib jaws.

The second brass must be made to just fit the strap when the back brass is in its place, and is small enough when the calipers, set as shown in Fig. 2373, and tried as shown in Fig. 2376, just fit the strap. This will insure that both brasses fit the strap when it is in its place on the rod.

When both pairs of brasses have been fitted to their straps, the latter should (if held by bolts) be bolted to their places on the rod, and the centre of the respective spaces for the brasses will be the location for the marks g, g, Fig. 2360. A pair of trammels should, however, be set to the proper length of the rod and these marks tested. If the strap is held by gibs and keys, as in the small end in Fig. 2360, the strap should be put on its place with the gibs in, and drawn up the rod by slowly forcing the key in until the mark g at that end stands in its proper distance from g at the other end, at which time the key should come through its proper distance.

The thickness of the brasses must be measured from these marks g, g to the crowns of the straps and the ends of the rod respectively. If the rod is of its proper length and the straps are in their proper positions, these marks will come in the centre of the space for the brasses. If, however, there is any error, as there is apt sometimes to be in very large rods, the course to be pursued depends upon the kind of rod end. If both straps are bolted to the rod end, the error may be divided equally at each end. If one end has a key and gib or gibs, but no bolt, as at the small end in Fig. 2360, the key brass may be made of such thickness as to butt against the end of the rod and meet the mark g.

For the large end, the thickness of the key brass, or, in other words, the distance d in Fig. 2378, must be taken after the face of the crown brass has been squared up, as described with reference to Figs. 2374 and 2375, the connecting rod strap being placed in such position that the key will be up in its proper place.

When the joint faces of brasses do not meet, but are left open to take up the wear, it is a difficult matter to properly adjust the brass bore to the journal. If the flanges of the brasses do not quite fit the length of the journal, as is very commonly the case, it is customary to tighten the key until the rod end can just be moved by hand so as to force the brass flanges against first one and then the other end of the journal. This is an approximate adjustment; and if the journal heats at all, the key is slacked back a trifle; whereas if it pounds, the key is set up a little. As a matter of fact, then, nothing is actually known of the precise fit of the brass to the journal; and while looseness may be detected by the pounding, the brass may be tight enough to cause undue wear without very sensibly heating the journal, especially if the latter is freely lubricated. If, however, the brasses fit the length of the journal, and do not butt, it is usual to drive the key in till the brasses bind the journal, and to then slack the key back to the necessary amount. What that amount should be cannot be stated, because it varies with the taper of the key and the force with which it is driven home. As a result, then, the operation is left to the judgment, or, in other words, to guess-work, of men, many of whom are not well experienced in the operation; while under any circumstances the actual fit is not positively known. A plan not infrequently adopted is to insert a piece of lead wire of small diameter between the brasses, the key is first driven tightly home, and then slacked back until the lead wire is just freed. It is estimated that the adjustment will then be correct; there is no actual certainty of the fit, however, even in this case.

Another objection is that the oil is apt to flow out of the opening, and the brass having communication with the oil cup is better lubricated than the other brass.

In cases where the brasses 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 brass is sometimes placed between the joint faces, and this piece is filed thinner to let the brasses 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 brasses butt, the key binds the brasses to the end face of the rod and the strap to the brasses, which if there is any wear sideways (as in locomotives), prevents the keys from wearing the sides of the key ways and the brass flanges 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, pass through the flange of one brass and abut against the face of the other, serving to adjust the fit of the brasses to the journal, and lock them in their adjusted position, locking at the same time the brasses 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 brasses should be marked so that the bore, when bored out, will leave an equal thickness of metal between the brass 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 brass 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 brasses in their places in the rod and fasten a centre piece in the brasses 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 brasses if the joint faces meet, and in the centre of the space between them if they do not meet.

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 brasses 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 brasses are bored true to their own faces, the bore of the brasses at one end of the rod shall stand parallel to the bore of those at the other end.

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

The reason that the jaws or box that receives the brasses 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.

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 brass bores at the fork end shall be parallel with the centre line b of the bore at the butt end; that the side faces of all the brasses 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 butt end as denoted by c, d; that the bores of the brasses shall be at the proper distance apart to make the length of the rod come right; that the brasses 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 butt 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 brasses 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.

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 brasses; 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 ways for the brasses 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 brasses at the butt end. Before filing up the side faces at the butt 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 butt end, a straight-edge should be applied, as at s and s′′, Fig. 2386, being pressed firmly to the side faces at the butt 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 brasses, 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 brasses. s is a square held firmly against the side face of a jaw, the brasses 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 brass and s the square. The brasses 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 brasses for boring. The joint faces of the brasses should form the centre of their respective bores; hence, all that is necessary, is to insure that the brasses 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 brass, 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 brasses in the strap, put in a piece of wood whereon the compasses 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 brasses, 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 brasses true to the ways that fit the rod jaws, and to the dotted circle, the bores will stand true in every respect.

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.

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.

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

To refit the brasses to the jaws of the strap, the flanges 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 flanges (of both pairs of brasses) that come on the same side of the rod, so as to keep the faces of the brasses leading fair.

The fit between the jaws is restored by riveting pieces of sheet brass to that side of the brasses 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 brass which are sometimes soldered as well as held by rivets. These rivets are screwed into the brass, being composed of softened brass wire riveted after being screwed in.

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

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

If the brass faces are to come “brass and brass,” that is, butt 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 brass so that it shall embrace one-half the journal diameter, which will be the case when the two brasses 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 brass 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 brass, and also in Fig. 2400, in which s is a square and b the brass shown in section, thus making the faces quite square.

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 brasses will be forced by the key-pressure in the direction of the respective arrows, and there will be a tendency to twist the brasses 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 brasses in the direction of e, f, and therefore to cause these to move in the direction of g, h, and as a result the brasses will spring the strap away from the rod, as shown at i, j.

To line up the brasses for length we proceed as follows: One of the liners adjusts the length of the rod and the other simply serves to set the key back to its proper height, so that it shall not pass too far through the keyway, as the wear of the brasses lets it down. Which of the liners will be the one by which to alter or adjust the length of the rod depends upon the design of the rod itself; but, in the case of all solid-ended rods, or those in which the position of the strap is fixed by means of bolts, it is the liner behind the end brass, as d, in Fig. 2402, as stated in the opening of this discussion, and it is the first one, therefore, to be fitted. The space at e is where the second liner requires to be placed, its thickness being that necessary to lift up the key from its bottom or lowest position, as shown in the cut, to the highest position.

In strap-ended rods in which the strap is not bolted to the rod, but moves farther upon the rod as the key passes farther through the keyway, it is the brass next to the rod end, as b, in Fig. 2403, by which to adjust the length of the rod, and its liner l is, therefore, the one to be fitted first; the space e is, in this case, the one to be fitted with a liner of sufficient thickness to lift the key up. It will now be noted that the thickness of l in both figures requires to be exact, so that the rod may be of correct length, which is necessary, so that there may be the same amount of clearance or space between the piston head and the cylinder cover when the piston is at the respective ends of the stroke. But the liners to fill the respective spaces e need not necessarily be of the exact thickness (although it is better that they should be), because if too thin the only effect will be that the key will pass farther through the keyway than otherwise. In considering in any form of rod which is the liner to be put in first to bring the rod to length, we have the general rule that the brass that moves in the strap or rod end when the key is moved farther through the keyway is the one to be lined last. The method of obtaining the proper thickness of the liners l, Figs. 2402 and 2403, are as follows: If the rods have been correctly made at first, the centre of the brass bores will be midway in the spaces for the brasses (denoted by f in the two figures). If the oil-holes in the strap or rod end (as the case may be) have been drilled in the centre of this space f as they should be, then the line g will represent the centre of f and the centre of the oil-holes, and all that will be necessary will be to place behind d and b respectively a liner of sufficient thickness to bring the joint face of these brasses (d and b) even with the line g. To ascertain the thickness of liner necessary for this purpose, suppose the case of a rod end of the design shown in Fig. 2402, then, with the strap off the rod, drive the brass d down until its crown face beds fairly against the strap c, and with a scriber mark on the inside face of the jaw of the strap a line coincident with the joint face of the brass, then set the brass up the strap until its joint face comes fair with the centre of the oil-hole or the central line g, and then mark a second line so that on taking the brass out of the strap there will appear two lines, and the distance between these two lines is the necessary thickness of liner. In the case of the form of rod end shown in Fig. 2403, the process would be as follows: Let the strap have placed in it the brass b only, place it upon the rod, and set it so that it binds the gib and key, when the key is lifted up to its required position, then, with the brass b bedding fairly against the rod end, mark on the strap a line coincident with the joint face of the brass as before. Then move the brass in the strap until its face comes fair with the centre of the oil-hole or line g, and mark another line, and the thickness between these lines is the thickness of liner required at l.

If the brass is to be lined sufficiently to merely bring the key up without respect to the length of the rod we may drive the key home as in Fig. 2404, and mark on it a line coincident with the edge a of the strap. We then lift the key up to its proper height and mark a second line, so that when removed from the keyway the key will have on it the two lines shown in Fig. 2405, a being the first and b the second line; and the difference between the width of the key at a and its width at b will be the thickness of the liner necessary to be placed behind the brass nearest to the key. To ascertain the precise amount of this difference (because a very small error as to this amount causes a great deal of extra labor), we set a pair of outside calipers to the width at a; and then passing the caliper points down to b, we keep one of the points even with the line b, and insert a wedge until it just fills the space between the other point and the side of the key, as shown in Fig. 2406, c being the wedge, which should be chalked along its surface so that, when inserted until it touches against the caliper point, the latter will leave a mark on the wedge, denoting exactly how far the wedge entered, and hence the exact required thickness of liner.

It has thus far been supposed that the joint faces of the brasses are made to come brass and brass, that is to say, butt close together from the key pressure, when the brass bores properly fit the journal. Suppose, however, that the joint of the brass is left open as in Fig. 2407, and in that case a strip of metal f, whose diameter equals that of the journal, may be inserted between the brasses as shown, and at its centre should be provided a small centre-punch mark, denoting the centre of the bore. A piece of this kind should be inserted in the brasses at each end of the rod and placed in the middle of the length of the bore, the centre-punch marks being to apply the trammels to. Or if the rod was made of correct length when new, and the bore of the brasses, therefore, requires to stand central in space f, Fig. 2403, then the pieces f, Fig. 2407, may be dispensed with by marking a line b, Fig. 2408, central to space f, Fig. 2403. Then put the strap on the rod (with the brasses, gib, and key in place), and pull the strap back to hold the key up to its proper height.

The two brasses should then be placed as far apart as possible in the strap, each bedding fairly against its back or crown. Then, using the joint face of the back brass as a straight-edge or guide, a line should be marked on the side face of the strap, this line representing the position of that face when the brass is bedded fairly home, and being shown in Fig. 2408 at a. This brass should then be moved forward until the bore of the pair of brasses at d, Fig. 2408, measures equal to the diameter of the journal (of the crank pin or of the cross-head pin as the case may be) and a second line b, also coincident with the joint face of the brass, should be marked upon the strap, and the strap will then have marked on it the two lines shown in Fig. 2409, in which it is shown removed from the rod; the distance apart of these two lines will be the thickness of the two liners combined, hence half this thickness will be the thickness necessary for each liner. Suppose, however, that it is not known whether the rod has been correctly made, and therefore it be unknown whether, in order to have the rod of the correct length, the brass bore should stand in the centre of the space or not.