Chapter XXVII: VICE WORK--(Continued) (1)

There are two principal kinds of connecting rods, first those in which the brasses fit in spaces provided in the solid rod, and which are known as solid-ended connecting rods, and second those in which the brasses 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 brass 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 brass. 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 brass, giving play to the brass 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 brass 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 brass 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.

Yet another simple form of solid-end connecting rod is shown in Fig. 2330, there being two brasses with a key on one side and a set-screw on the other. In this case, as soon as either brass 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 brasses sideways in the rod, and furthermore the brasses 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 brass A has a flange, as shown in Figs. 2331 and 2332 at A, which secures it to the rod end at the back. The top or key brass 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 brass 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 brass, the taper for the key should be cut in the rod so that the edge which meets the brass will stand square across the opening for the brass; in this way the back of the brass 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 brass, 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 brasses wears, and the lost motion incident thereto is taken up (by driving in the key) the location of the brasses 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 pass through the rod, slips of iron termed liners are inserted between the backs or bedding faces of the brasses 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 brasses in the rod end may be adjusted so as to bring the brass back to its original position and restore the rod to its proper length, and in doing so the back brass, as distinguished from the key brass, is the one to be lined first.

In the rod ends shown in Figs. 2333 and 2334 the joint faces (that is the faces where the brasses 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 brass, 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 brass bores), while the thickness of that placed behind B would simply act to prevent the key from passing 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 brasses and the stem of the rod, as in Fig. 2334. In this latter case the thickness of liner placed behind the key brass B (as the brass against which the key bears, or the brass next to the key, is always termed) would adjust the length of the rod, while the thickness of liner placed behind the back brass (as the other brass is termed) would be the one to adjust the distance the key would pass through the keyway.

In this form of rod end, as in many other solid-ended rods, the flange or collar of the crank pin, if solid with the pin, requires to pass through the opening in the rod end which receives the brasses. This may be accomplished by making that opening large or wide enough to pass over the crank-pin collar (which will increase the width of the brasses, 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.

It will be noticed in Fig. 2331 that the brass B does not fill the space in the rod. This is because that brass has to pass in over crank-pin collar and push up into the journal after it is in the rod. To make this space as small as possible, and to enable giving the crank pin as large a collar as possible, the key brass is sometimes beveled off, as shown in Fig. 2336 at A B. Another form of this rod end is shown in Fig. 2336, in which there are two keys to the brasses, the object being to adjust the keys to maintain the rod of its proper length. In order to facilitate making this adjustment, there should always be upon the face of the rod end centrepunch marks, as shown in Fig. 2338 at F and G, or else two deep marks, as shown at C D in Fig. 2337. Then, in lining up the brasses to set the key back, the rod may be restored to its original length by putting behind the back brass a piece of metal of such thickness as will bring the centre of the bore of the back brass B even with the centrepunch or other marks. This being the case, it does not matter about the exact thickness of the piece of metal put behind the other brass, since a variation in that will only act to let the key come more or less through the rod end without affecting the length of the rod. In Fig. 2337 is shown a form of rod end sometimes used. The end being open, the brasses pass through it. In this case the whole strain of the pull of the rod falls upon the edge of the gib at top and bottom of the strap, causing the gib to wear out very fast; furthermore, the back brass condenses the metal at the back of the brass opening, acting to pene it and throw the points of the rod end open, which it always does, the jaws of the gib imbedding in the jaws of the rod. This opening of the rod jaws makes the brasses loose in their places; hence this is a weak and undesirable form of rod end, though very convenient to take on and off. In Figs. 2338, 2339, 2340, and 2341 is shown a form of solid-ended rod of more modern construction. In this case a wedge A is used instead of a key, being adjusted by screws passing through the rod at the top and bottom, it being obvious that the set-screws may have check-nuts added. B is the back brass, and C the key brass. In this case the flange of the brass goes next to the crank pin, and a plate D is provided to serve as a flange on the front face of the brass. In Fig. 2338 this plate is removed to show the wedge A; but it is shown in the plan view, 2339, and the end view, 2340, and by itself in Fig. 2341. A groove is cut on each side of the two brasses and the plate spans the brasses, passing up the groove being held in position by a screw at E. The opening for the brass (in the rod end) is here shown wide enough for the rod end to pass over the collar of the crank pin, but in many cases, with this as well as with other forms of solid-ended rods, the crank pin may be made plain--that is, without a flange--and have a washer secured by a screw, so that by removing the washer the rod may be put on with the brasses already in place, and made no thicker (at the joint face) than is necessary for strength. In Fig. 2342 is shown what may be termed a clip-end connecting rod, the screw closing the rod end (to take up the wear) against the spring of the metal. It is obvious that in this case the hole may receive a brass bush split as is the rod end and secured from turning by a pin. Fig. 2343 presents another form of solid-end rod, which admits of the use of a brass having a flange on both sides of the strap, and will take on and off by removing the cap B. If the crank-pin collar is solid, the brasses must be placed on the crank pin, and the rod, with the wedge in place, lifted or lowered to the brasses; but if the crank pin has a washer and bolt, the rod may be put together and slipped on its place.

A compromise between the solid and the strap-rod end is shown in Fig. 2344, which represents a design used upon the fast engines of the Pennsylvania Railway. The piece A takes out to enable putting on the rod or taking it off, A being secured in position by the bolt and nuts shown. This forms a solid and durable rod that is much less costly to make than strap-ended rods.

The simplest form of strap-ended connecting rod is that shown in Fig. 2345; S is the strap, secured to the rod end by the key D and gib C. A is the top, and B the bottom, or crown brass, and E the set-screw for securing the key in its place. [When the rod ends are forged in separate pieces, to be afterwards welded to the stem of the rod after the strap brasses are fitted up (which is done for convenience in handling them while fitting them up), they are termed stub ends.] This form of rod affords great facility for connection with the journals as the strap is easily removed. As the strap, however, is only secured to the rod by the gib and key, and as these have a small amount of area on the sides, it is not unusual to employ two gibs and one key, as in Fig. 2346, which holds the strap more securely, and more effectually prevents its movement sideways upon the rod end. In rods in which gibs and keys alone are used to hold the strap to the rod, the strap moves along the rod as the key passes farther through the strap, and the fit of the strap to the rod must be easy enough to permit of this motion; hence it cannot be locked to the rod. This, however, may be done by the employment of a bolt as well as a gib and key, as is shown in Fig. 2347. The edge of the gib here abuts against the back of the top brass, or key brass, as it is sometimes termed, which is objectionable, inasmuch as that it is apt to indent the brass, as shown in Fig. 2348 at B. This causes the bore to close at A, and causes the journal to heat, while it makes the brass fit loosely between the jaws of the strap, because it stretches the metal at the back of the brass, which has the same effect as pening it with the hammer.

In Fig. 2349 is shown an end of a connecting rod, such as is employed on American locomotives, the use of a gib being dispensed with, and the strap being held by two bolts. To prevent the edge of the key from imbedding in the brass, a piece of hardened steel is sometimes placed between the key and the brass, as shown in the figure.

In some designs this method is reversed, the gib being prolonged in a screw-thread, as shown in Fig. 2350, and the key head is carried over as shown. Two wing nuts are provided for adjusting the key, which enables its adjustment without the employment of a wrench or hammer.

To prevent the end of the set-screw from raising a burr on the key, which would prevent its easy motion through the keyway, a shallow groove is sometimes cut along the key, as in Fig. 2351 at A, the end of the set-screw binding on the bottom of that groove.

In other forms of rod a gib and key are used as well as two bolts. This not only holds the strap very firmly, but it prevents to a certain extent the pening of the back of the brass, explained with reference to Fig. 2348. It is obvious that in the absence of a gib the key moving under friction against the brass stretches the metal more than a gib that presses against the brass, but has no motion endways.

In Fig. 2352 the strap is held by bolts having nuts at each end, instead of a solid head at one end and nuts at the other. The single nuts at the top serve to draw the bolts out when the rod is to be taken apart, thus saving the use of the hammer for that purpose.

In Fig. 2353 is shown a form of rod in which the strap is held by two dies A B, and a bolt which passes through the strap, the dies, and the rod end.

In Fig. 2354 is a form of rod end in which the strap ends are keyed against abutments on the rod by means of the key A. The abutments and strap ends being bevelled, keying up the strap with A closes it down upon the rod.

In Fig. 2355 is a form of rod end largely used upon marine engine work; A is the end of the rod, B, B the brasses, and D, D bolts passing through the brasses. Here we have no means of correcting the alteration of length due to the wear, unless a line is marked on the rod end, as at C, and the distance that line should stand from the centre of the brass bore is marked beside it, as is denoted by the figure in the cut, indicating that the line should stand 9 inches from the cuts of the brass bore.

In general practice the inside jaw faces of connecting rod straps and the faces of the rod are made parallel, which serves very well when the duty and wear is not great; but when the wear and tear is great, as in locomotive work, it is much better to make them taper; indeed, they are in any event better taper, because in that case the brasses can be made a tighter fit. The reason for making them parallel is because they can be more readily planed so than taper; but a parallel strap is more difficult to fit, and cannot be made so good a fit as a taper one, even when new, while it is very much more difficult and expensive to repair.

When the faces of the stub end (or, more properly speaking, of the block) are parallel one to the other, and the inside faces of the strap are also parallel, the strap must be made a very easy fit to the block, in order to be an equal fit from end to end; for if the strap fits as tightly as it should to be a good job, it will, when put on the rod, spring open, fitting across A, Fig. 2356, only; this because the strap springs open from contact at A. The fit, then, can only be such as will not have force enough to spring the strap open, and this is very small indeed even in a very strong strap. It is within the mark to state that in a strap measuring 4 inches between jaws, at A in Fig. 2356, it can be forced by hand on the rod sufficiently tight to spring them open 1/16th of an inch at B, B. When the brasses are fitted into the strap a second difficulty arises, inasmuch as they must be made a very easy fit, or else they will spring the strap open so that it will neither fit at A nor at B, whereas it is desirable that the bottom brass drive home, and the top brass, or one nearest the rod, just push home by hand.

When the rod requires repairing a more serious difficulty arises. Suppose, for example, that the strap requires refitting to the rod, then it must evidently be closed between the jaws, especially if the rod end requires filing up, as it usually does. Now the jaws being parallel cannot be closed without being taken to the blacksmith shop and closed across the crown, as at A in Fig. 2357; for if the jaws are closed (as they might be) by pening the corners B, C the jaws would close as denoted by the dotted lines. The brasses will have to be made larger than the diameter at D, in order to fill the space at A, and will be an easier fit as they pass from D to A, whereas the opposite should be the case. The strap must therefore be closed across A in the blacksmith's fire; this will scale the crown end and render it necessary to file down the whole of the surface on each of the side faces of the strap and rod in order to make them parallel, as they must be to have the flanges of the brasses fit when home in the strap.

The blacksmithing will in most cases render it necessary to file out the keyways, and this again entails the making of a new gib and key. All this extra work may be avoided by making the block and strap a little taper. But before proving this it may be noted that when the rod is made parallel the strap may be made to fit tightly by making the jaws taper, as shown by dotted lines in Fig. 2357; so that when the strap is on the rod, and the jaws spring open by reason of the close fit, the fitting surfaces will be parallel. Such a construction would be faulty however, for the brasses would fit too tight when entering the strap, and get easier as they passed to their places, whereas, as already stated, the exact opposite should be the case.

Let us now observe the advantages of a strap, whose inside faces are made as in Fig. 2358; smaller at A than at B, and also at C than at D, while the thickness from A to B is greater than that from C to D, while the widths C D are less than the corresponding width of the rod.

First, as to fitting the strap to the rod. It may be made so tight to the rod that it will only just pass on when pushed by the hand.

Second, this will render possible a tighter fit than would be possible with a parallel strap and rod.

Third, the width B A being taper, the brasses may be easier made a good fit, because there will be some metal to fit on after they enter at B.

Fourth, the brasses may be made a tighter fit, the bottom brass being tight enough to spring the strap a trifle, easing but not destroying its fit on the rod.

Fifth, the top brass may be made a handsliding fit to the strap without springing the strap open, which being already under a tension because of the spring due to the bottom brass, will be more rigid and permit of a tighter degree of top brass fit, without springing open and away from the rod.

Sixth, this will leave the bottom brass a tight driving fit, and the top a hand sliding fit, which is desirable, because the top brass has to be taken out to get the rod off while the bottom brass remains in its place.

Seventh, what is of more consequence than all, the strap can be more easily and cheaply refitted to repair it. Thus, in Fig. 2359, suppose the strap to have been closed by pening at D; then whether the end D will be narrowed will depend on the amount the strap was closed, and the amount of taper it had before closing. Let us take, however, the most unfavorable conditions, and suppose that the amount of taper was so small, and the amount of closing by pening so great, that the jaws were made taper and smallest at D. Then the amount to be filed off to bring the width of jaw correct, and a fit to the strap, will be less than if the strap jaws were formed as in Fig. 2357, as will be seen by comparing Fig. 2357 with Fig. 2359, the amount to be filed away being that between the dotted and the full lines in both figures; the amount of closure being the same in the two figures.

But there is another great advantage, inasmuch as in pening, the strap may be pened and tried on the rod, the strap being pened and tried alternately until the required fit is obtained, which is not practicable with upsetting in the blacksmith's shop.

Again, the keyways in the strap will not be set out of true with those in the rod, as they are apt to be when upsetting is resorted to, nor will the strap be scaled; hence the side faces will require but little filing.

Furthermore the step may be located so as to come against the rod end when the wear has let the key down, and this will prevent the strap from passing too far upon the rod, and, therefore, tend to prevent the rod length from being improperly altered from errors in the thickness of the liners placed behind the brasses to take up the wear.

FITTING UP CONNECTING RODS.--The method of fitting up a connecting rod depends entirely upon its size. Very small rods to be made in numbers are usually got out by means of special devices which leave the fitter but little to do; indeed, sometimes the machine work is so accurately and finely fitted and finished as to finish the rod without the aid of the vice hand, save to put it into its place upon the engine or machine. As, however, the dimensions of the rod increase, this method of manipulation is in practice departed from, and the filing, fitting, and adjusting operations increase. In any event, however, the principles to be observed in the manipulation are the same, because the points to be observed in the fitting by hand work must be accomplished by the machine if the rods are to be finished by machine work.

Let Fig. 2360 represent a connecting rod; A representing the centre line in the side, and F the centre line in the edge view, and it is obvious that the axial lines, B and C, of the brass bores must stand at a right angle to line F, and be parallel to each other, because the journals on which they fit will do so. Furthermore, the faces of the brasses, as E, must stand their proper distance from the centre line F, this distance being at each end respectively half the whole width D, and the faces E must be in the same plane whatever their widths may be. The centre lines A and F are imaginary lines not worked to (except it be in marking or lining the rod out for the planing operations); but the method employed to fit up the rod must be such as will make all parts true to those lines if they were tested by them.

The process of fitting up a connecting rod may be tersely stated as follows: 1st, the rod is planed; 2nd, the straps are planed; 3rd, the straps are fitted to the rods; 4th, the straps are drilled and bolted to the rod; 5th, the keyways are cut, and the keys and gibs fitted; 6th, the side faces of the rod ends are again planed with the straps on; 7th, the brasses are fitted and the rods marked off for length and the brasses bored; and, 8th, the file finishing and polishing done.

In the case of very large rods the two ends are made and fitted up as separate pieces, and are afterwards welded to the body or stem of the rod, and the setting of the ends true one to the other after the welding affords such an excellent insight into the alignment of rods that it may be well to describe it. First, then, the rod being laid on its side, two straight-edges, or rather winding strips, S and S´, Fig. 2361, are placed on the side faces, and the rod will be set in this direction when their ends A, B, C, D, appear parallel when sighted by the eye. If the winding strips are adjusted to stand straight across the rod, and, therefore, parallel one to the other, any twist or wind in the two rod faces will be very plainly discernible by the sighting process. The rod is then stood on edge, as in Fig. 2362, to test the alignment of the side faces. A straight-edge S is pressed firmly against one of the faces, as H in the figure, with the other end elevated as shown. The elevated end is then lowered, the motion serving to keep the end fairly bedded against face H. The distance, I J, Fig. 2363, is then measured. The straight-edge is then used in the same manner on the other side of the rod as at S in the figure, and the distance K L is measured, the setting in this direction being correct when distances I J and J K are equal. The straight-edge is then applied to the edge faces of end H of the rod, as in Fig. 2364, at M and at N, the distances O, P, are made equal. During these operations a straight-edge is applied along the body of the rod to see where to set it to effect any required adjustment, and if that body is straight the adjustment is made near the end at which the straight-edge is pressed to the rod.

The setting of the small end I is effected in the same manner, but the straight-edge will in this case fall over the face at the larger end, as is shown in Fig. 2365; hence, instead of measuring, lines as G and T are marked coincident with the edge of the straight-edge and the distances T U, I G, are made equal. Winding strips are applied to the edge faces as well as to the side faces, and as making one adjustment or alignment may alter another, the whole process must be repeated until the whole of the tests prove the setting to be true.

Now suppose the rod to have been forged solid and all these faces to have been made true in the planing, and the first operation is to fit the straps to the rod ends. The strap should be put in place on the rod and moved laterally, when the centre of its motion where it moves the least will be the place where it binds and therefore requires filing. If its side faces come atwist with the side faces of the rod end, as shown in section in Fig. 2366, either the faces of the rod end or the inside faces of the jaw are out of square as denoted by the dotted lines. In any event the face E, Fig. 2367, of the rod end should be surfaced true and made at a right angle to the side face, and if to be made parallel to M, also at a right angle to K, a square and a surface plate are used to test them. If the diameter J is to be smaller than that at H, then the angle of both face E, and its opposite, should be equal with reference to K. These faces should be finished by draw-filing, with the file marks lengthwise of the rod. To fit the strap, proceed as follows: To find where it requires filing, place it on the rod (having previously put red marking on the rod end), and move it endwise and sideways, observing where the least motion takes place when the strap is moved sideways by pressing its crown end, for this point of least motion is always where it fits the tightest. To test the jaw faces for being square apply a straight-edge S, and a square P, Fig. 2368, pressing S against the strap, and P firmly against S.

When the strap shows to bed well on the rod and its motion is an ambling one (and not a pivoted one), it fits properly, and if both rod and strap have been filed square, their side faces will come fair or even. The keyways being drilled, may then if necessary be filed out, for which purpose it is necessary to bolt the strap to the rod, a process that requires very skilful treatment, because if the tightening of the bolts moves the strap on the rod, or if the strap be moved on the rod after the clamp is tightened, the keyways will not come fair when the clamp is taken off. In Fig. 2369 the strap is shown held to the rod by plates C and bolts B, the rod being shown in position ready to file out the keyway. It is better, however, to let the side face of the rod stand vertical as the strap will stand steadier that way. The strap should be set fair with the outside faces, which will bring the keyway fair if it is properly located. The bolt nuts should be tightened gradually, first one a little and then another, going over all four once or twice before they are fully tightened, and if the strap is not fair when they are all tight, all must be loosened before the strap is adjusted, or the clamp pressure will cause the strap jaws to spring out of true, and the keyways will not come fair when the clamp is removed.

Should the keyways not come fair when the strap sets fair on the rod the strap may be set to accommodate the keyways, and thus save filing, but this must be done before clamping it to the rod end. Care must, however, be taken to see if cutting the strap out to suit the keyway may not leave too little metal on one side of the keyway when the strap is subsequently planed.

The sides of the keyway should be filed true to a surface plate, using a well-bellied file and as stout a one as possible, so that it may not bend under the pressure, and file away the edges of the keyway.

The keyway should be made parallel to the side face of the strap, so that it may be fair with the centre line F in Fig. 2360. It should be made of equal width throughout, a piece of iron being used as a gauge in place of the key, and this same piece of sheet iron will serve as a gauge to plane the keys to thickness.

The corners of the keyway, if to be made square, should be filed out with the corner of a smooth half-round file, because the corners even of safe-edge files do not come up sharp enough.

For filing out the end faces of rectangular keyways, a square file with both edges safe must be used, the safe edges being on opposite sides of the file. For roughing out, a taper square, but for finishing, a parallel, or equalizing file is preferable.

The next operation is to fit the keys and gibs. The key should first be fitted and should be filed true to a surface plate, for in no other way can a really good reliable gib be obtained, no matter how well the keys may have been planed or milled. It should be filed a tight fit to the keyway so that it may be used (with a light coat of red marking) to show tight places in the keyway, driving the key in for that purpose from first one and then the other end of the keyway. If, however, it is driven too forcibly, it may seize or cut, and it will be difficult to get it out, besides damaging both it and the keyway. When the keys are reduced so that they will drive lightly into the keyway, they should be tried in the rod and in the strap separately, moving the key laterally or edgeways, so that it may mark any high places in the keyway of either of them.

The finished key and gib should be left tight enough, that they will hold themselves in any position in the keyway of the strap or of the rod when standing vertical.

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.