Chapter XXVIII: Erecting (2)

In erecting pipe it is best to begin at one end and screw each successive piece firmly home to its place before attaching another, so that the lengths of the pieces may be accurate and not vitiated by screwing them up and causing them to enter farther into the fittings. If it is probable that the piping may have to be taken down after erection, it should be put up at first screwed together rather tighter than will be necessary, as the thread fits become eased by being moved one within the other. This is especially the case with brass fittings, upon which it is best in cutting the lengths of pipe to have it of full length, as the threads will conform to each other sufficiently to cause the pipe to enter a thread or so farther if the pipe be rotated back and forth a few times in the fitting.

The fit should in all cases be made by tightness of thread fit, and not by the union or elbow face jambing against the end of the thread or the pipe, as joints in which this is the case will usually leak if used under pressure.

The thread of both the pipe and the fitting should be smeared with a thick lead paint. If the pipe is to be used as soon as erected, plain red lead and boiled oil should be used for the paint; but if it may stand a few days it is better to mix white and red lead in about equal quantities, as this, if given time to dry, makes a tighter job. The quantity of this paint should not be more than will thinly cover the threads, otherwise it will squeeze out when the pipes are screwed home, and falling from the end of the pipe within the fitting be apt to be carried by the steam or water to the valves, and getting between them and their seats cause them to leak. The iron cuttings should be carefully cleaned both from the pipe and the fitting for the same reason.

In cases where the piping may require to be used under heavy pressure as soon as erected, it is a good plan to use dry red lead in varnish, thoroughly hammering it to mix it well, and thinning it after it has been so hammered.

In case of emergency a loose pipe may be somewhat improved by wrapping around its thread a piece of lamp wick saturated with this varnish lead, beginning at the end of the pipe and wrapping the thread from end to end.

It is preferable that the stem of the valve stand nearly horizontal, so that any water of condensation may pass freely away with the steam and not collect and lie in the pipe as it does when vertical. If it be quite horizontal the water of condensation will drip through the stuffing box; hence it is better that it stand 10 or 12 degrees from the horizontal.

It is better in all cases to purchase nipples than to make them by hand, because when made in a machine the threads are more true to the axis than those made by hand; especially is this the case in short nipples in which there is not sufficient length to use the guide socket when engaged in threading the nipple with the hand dies.

It is a very good plan in making such short nipples to cut them off the end of a length of pipe that has been threaded by machine, and to screw on the threaded end a coupling. Into this coupling a piece of pipe may be threaded to afford a hold in the vice. If then the nipple is long enough, a guide to suit the size of the nipple may be used in the threading dies, or a guide socket to fit the diameter of the coupling may be used.

A globe valve should be so placed on the pipe that the pressure will, when the valve is closed, fall on the bottom face of the valve, so that the steam may be shut off while the valve stem is being packed.

Cotton lamp wick plaited to fit the packing space, and well oiled, is as good as anything to pack the stem with.

In taking old pipe down a refractory joint may be sometimes loosened by striking it with a hammer while it is under full pipe tongs pressure; or these means failing, the elbow or tee may be heated, which should be done as quickly as possible, so that the fitting may be hotter than the pipe. A very good method of doing this, where it is desired to save the fitting, is to pour red-hot lead over the fitting.

If it is not important to save the fitting, it may be split by a flat chisel, or by cutting a groove along it with a narrow cape chisel; or if the pipe is free the elbow may be rested on an anvil and hammered around its circumference, which will either free it or break it, if of cast iron.

When pipes are to be taken down and re-erected elsewhere they should all be marked to their fittings and places before being taken down, as this will preserve their lengths as near as possible for re-erection. Black japan is an excellent marking for this purpose because it dries quickly.

RE-FITTING THE LEAKY PLUGS AND BARRELS OF COCKS.--When a cock leaks, be it large or small, it should be refitted as follows, which will take less time than it would to ream or bore out the cock or to turn the plug, unless the latter be very much worn indeed, while in either case the plug will last much longer if refitted, as hereinafter directed, because less metal will be taken off it in the re-fitting.

After removing the plug from the cock, remove the scale or dirt which will sometimes be found on the larger end, and lightly draw-file, with a smooth file, the plug all over from end to end. If there is a shoulder worn by the cock at the large end of the plug, file the shoulder off even and level. Then carefully clean out the inside of the cock, and apply a very light coat of red marking to the plug, and putting it into the cock press it firmly to its seat, moving it back and forth part of a revolution; then, while it is firmly home to its seat, take hold of the handle end of the plug, and pressing it back and forth at a right angle to its length note if the front or back end moves in the cock; if it moves at the front or large end, it shows that the plug is binding at the small end, while if it moves at the back or small end, it demonstrates that it binds at the front or large end. In either case the amount of movement is a guide as to the quantity of metal to be taken off the plug at the requisite end to make it fit the cock along the whole length of its taper bore.

If the plug shows a good deal of movement when tested as above, it will be economical to take it to a lathe, and, being careful to set the taper as required, take a light cut over it. Supposing, however, there is no lathe at hand, or that it is required to do the job by hand, which is, in a majority of cases, the best method, the end of the cock bearing against the plug must be smooth-filed, first moving the file round the circumference, and then draw-filing; taking care to take most off at that end of the plug, and less and less as the other end of the plug is approached. The plug should then be tried in the cock again, according to the instructions already given, and the filing and testing process continued until the plug fits perfectly in the cock. In trying the plug to the cock, it will not do to revolve the plug continuously in one direction, for that would cut rings in both the cock and the plug, and spoil the job; the proper plan is to move the plug back and forth at the same time that it is being slowly revolved. As soon as the plug fits the cock from end to end, we may test the cock to see if it is oval or out of round. The manner of testing the cock is as follows:--

First give it a very light coat of red marking, just sufficient, in fact, to well dull the surface, and then insert the plug, press it firmly home, and revolve it as above directed, then remove the plug, and where the plug has been bearing against the surface of the cock the latter will appear bright. If, then, the bore of the cock appears to be much oval, which will be the case if the amount of surface appearing bright is small, and on opposite sides of the diameter of the bore, those bright spots may be removed with a half-round scraper.

Having eased off the high spots as much as deemed sufficient, the cock should be carefully cleaned out (for if any metal scrapings remain they will cut grooves in the plug), and the red marking re-applied, after which the plug may be again applied. If the plug has required much scraping, it will pay to take a half-round smooth file that is well rounding lengthwise of its half-round side, so that it will only bear upon the particular teeth required to cut, and selecting the highest spot on the file, by looking down its length, apply that spot to the part of the bore of the cock that has been scraped, draw-filing it sufficient to nearly efface the scraper marks. The process of scraping and draw-filing should be continued until the cock shows that it bears about evenly all over its bore, when both the plug and the cock will be ready for grinding.

Here, however, it may be as well to remark that in the case of large cocks we may save a little time and insure a good fit by pursuing the following course, and for the given reasons. If a barrel bears all around its water-way only for a distance equal to about 1/16th of the circumference of the bore, and the plug is true, the cock will be tight, the objection being that it has an insufficiency of wearing surface. It will, however, in such case wear better as the wearing proceeds. Plug and barrel being fitted as directed, we may take a smooth file and ease away very lightly all parts of the barrel save and except to within, say, 3/8 inch around the water or steam-way. The amount taken off must be very small indeed, just sufficient, in fact to ease it from bearing hard against the plug, and the result will be that the grinding will bed the barrel all over to the plug, and insure that the metal around the water or steam-way on the barrel shall be a good fit, and hence that the cock be tight.

The best material to use for the grinding apparatus is the red burnt sand from the core of a brass casting, which should be sifted through fine gauze and riddled on the work from a box made of, say, a piece of 1-1/2 pipe 4 inches long, closed at one end and having fine gauze instead of a lid.

A very good material, however, is Bath brick rubbed to a powder on a piece of clean board. Neither emery nor ground glass is a good material, because they cut too freely and coarsely, which is unnecessary if the plug has been well fitted.

Both the barrel and the plug should be wiped clean and free from filings, &c., before the sand is applied; the inside of the barrel should be wetted in and the plug dipped in water, the sand being sifted a light coat evenly over the barrel and the plug. The plug must then be inserted in the barrel without being revolved at all till it is home to its seat, when it should be pressed firmly home, and operated back and forth while being slowly revolved. It should also be occasionally taken a little way out from the barrel and immediately pressed back to its seat and revolved as before, which will spread the sand evenly over the surfaces and prevent it from cutting rings in either the barrel or the plug. This process of grinding may be repeated, with fresh applications of sand, several times, when the sand may be washed clean from the barrel and the plug, both of them wiped comparatively dry and clean, and the plug be re-inserted in the barrel, and revolved, as before, a few revolutions; then take it out, wipe it dry, re-insert and revolve it again, after which an examination of the barrel and plug will disclose how closely they fit together, the parts that bind the hardest being of the deepest colour. If, after the test made subsequent to the first grinding operation, the plug does not show to be a good even fit, it will pay to ease away the high parts with a smooth file, and repeat afterwards the grinding and testing operation.

To finish the grinding, we proceed as follows: Give the plug a light coat of sand and water, press it firmly to its seat and move it back and forth while revolving it, lift it out a little to its seat at about every fourth movement, and when the sand has ground down and worked out, remove the plug, and smear over it evenly with the fingers, the ground sand that has accumulated on the ends of the plug and barrel, then replace it in the barrel and revolve as before until the plug moves smoothly in the barrel, bearing in mind that if at any time the plug, while being revolved in the barrel, makes a jarring or grating sound, it is cutting or abrading from being too dry. Finally, wipe both the barrel and the plug clean and dry, and revolve as before until the surfaces assume a rich brown, smooth and glossy, showing very plainly the exact nature of the fit. Then apply a little tallow, and the job is complete and perfect.

In place of the tallow a soft paste of good beeswax and castor oil is an excellent application, the two being heated in order to thoroughly mix them.

The grinding material must be frequently changed to produce smooth work, because if the grinding cuttings accumulate in it, they will scratch and score the work. Indeed, it is a good plan when convenient, to hold the cock and plug under water while grinding them, and to occasionally lift the plug out, so as to wash out the cuttings.

The surface of a well-ground plug will be in all cases polished, and not have that frosted appearance which exists so long as active grinding is proceeding, and all that is necessary to produce this polish is to well work the plug in its barrel while keeping it quite clean.

FITTING BRASSES TO THEIR JOURNALS.--Brass bores always require fitting to their journals after having been bored, because the finished hole is not a true circle, but too narrow across the joint face, as at F in Fig. 2475, in which the full lines represent the form of the brass before, and the dotted line its form after being bored and released from the pressure of the devices or chuck that held it while it was being bored. This almost always occurs to a greater or less degree, and it arises from local strains induced from the unequal cooling of the casting in the mould, which strains are released as the metal is removed (in the process of boring) from the surface of the bore. It would appear, however, that if the finishing cut taken by the boring cutter be a very fine one it should leave the hole true and round, but the pressure which is placed upon the bearing to hold it against the force of the cut prevents the bearing from assuming its natural form until released from that pressure.

If a bearing be bored to very nearly its finished size and first released altogether from the pressure of the holding chuck, or other device, and then re-chucked, it is probable that the finished bore would be practically quite round and true, but such re-chucking is not the usual practice.

Suppose, however, that the bearing shown in Fig. 2475, be properly fitted to a journal, still improper conditions arise from wear, because the area of the surface D becomes from the weight and from vibration condensed, and finally it stretches, causing the bore at F to close upon the journal and bind it with undue friction.

If the shape of the bedding part of the brass, or bearing, be such as shown in Fig. 2476, the surfaces A B and C will condense and stretch, closing the diameter of the bore at E and making the sides G G fit loosely in their places. It is to be observed that a similar condensation of the metal occurs to some extent around the bore of the bearing; but this surface is being continuously worn away by the journal, and it is, therefore, at all times less stretched and condensed than that on the bedding surface.

There is, therefore, a constant action causing the brass to bind unduly hard at and near its joint face E, Fig. 2476, and thus to cause heating and undue abrasion and wear. To prevent this it is necessary to ease away that part of the brass bore, as is shown in Fig. 2477 from J to K, clear of the journal.

But in the case of bearings receiving thrust, as in engine main bearings, the line of pressure is in a horizontal direction; and hence the most effective bore area to resist that pressure has been removed. Furthermore, the bearing area of the brass bore has been reduced, thus increasing the pressure per square inch on the remaining area.

The methods employed to avoid this evil are as follows:--In the form shown in Fig. 2478 the joint faces are at an angle instead of being horizontal and parallel to the line of the thrust, or the joint faces may be made to stand at a right angle to the line of journal thrust, so that the crown of the brass will receive the thrust. But the brasses will still close across the joint faces (as already described) as the wear proceeds, and the areas from J to K in Fig. 2477, must still be eased away, requiring frequent attention and giving a reduced bearing area. Furthermore, in proportion as the line of the joint faces of the brasses is at an angle to the line of thrust, the strain on the top or cap brass will fall on the bolts, so that if those joint faces be at a right angle to the line of thrust, the whole strain of that thrust will fall on the bolts that hold the cap and cap brass.

Another plan is to make the bearing in parts, as in Fig. 2479, in which the top and bottom parts of the bearing extend to the joint face on one side, but admit a chock or gib, A in the figure, which may be adjusted by a set-screw as shown. By this means the bearing area may extend all around the bore. In some cases two of such chocks and set-screws, one on each side of the journal, are employed.

In place of the set-screws, whose ends, from receiving the pressure of the thrust, are apt to imbed themselves into the chock and to thus loosen the adjustment, wedges lifted by bolts passing up through the cap, as shown in Fig. 2480, are employed, being preferable to the screws.

In the Porter Allen engine the wedges pass clear through the bearing, as in Fig. 2481, so that they may be pushed up after the manner of a key and their pressure against the side chocks judged independently of the nuts at the top.

In some designs the top and bottom parts of the bearing are free to move in the line of the thrust, and the side chocks or blocks alone are relied on to resist the thrust.

When the brasses are in two halves, they may be fitted so as to have a known degree of bearing pressure upon the journal, and the fit may thus be accurately adjusted, in which case they will wear a long time before requiring re-adjustment. On the other hand when the side chocks are used the wear in the line of the thrust may be taken up as it proceeds. In one case the attending engineer cannot alter the fit of the bearing nor the alignment of the shaft, while in the other he can do both. Thus the facilities that enable him to make these adjustments properly also enable him to make them improperly. But this would be of no consequence, providing it could be determined whether the adjustment were improving the conditions without first making it. With an engine at rest it is easy to determine, by means of the connecting rod, whether the chock adjustment is correct, so far as the adjustment of the shaft is concerned, but it is not easy so to determine the pressure of the chock on the journal; nor when each chock has two adjusting screws is it easy to determine when they both bear alike.

When the bearing is in four pieces, and three of them have two screws each, it is still more difficult to operate all so as to have the bearing equal on the journal. The fit to the journal can only be determined by the results: if too easy, the bearing pounds; if too tight, the bearing heats and wears.

But undue wear may take place without heating, and this is one of the greatest objections to this method of adjustment.

A design of bearing used in American locomotive practice is shown in Fig. 2482. Here the joint faces C, B of the brass is bevelled, fitting into a corresponding bevel in the box, which prevents the brass from closing across the joint face; hence, the bearing on the journal may extend all around the brass bore from the oil cavity A to the edges B C. The brass is, in this case, forced to its place in the axle box under hydraulic pressure, and this pressure springs the box open at H, making it wider; but when the box is put to work the brass compresses somewhat, and its surfaces conform more closely to the bedding surface of the box than when first put in, and this causes the box to close slightly at H.

To prevent this closure from carrying the brass with it and close it across the joint face (as in the case of the brass shown in Fig. 2476) the following plan is adopted. The brasses, after having been turned in the lathe, are filed along the entire surface (on each side) for a distance of about 1-1/2 or 2 inches, so as to clear the bore of the box near the bevels B, C. When the box is put into the hydraulic press, to have the brass forced in, a centre-punch mark J is made, and part of a circle L L is struck; when the brass is home in the box the arc of circle K is made, the distance between K and L showing how much the box has been sprung open by the brass; the amount allowed is about 1/32 of an inch. If, as the brass is pressed in, it is found that this will be exceeded, it is taken out and eased. When the engine is running and the boxes spring to some extent they do not carry the brass with them, because the sides being eased away gives liberty to the box to come and go slightly; the bevels also tend to keep the brass bore open.

Here, then, the brasses may be fitted to align the axle perfectly, and it is not permitted to the engineer to alter that alignment, while at the same time the fit of the brass to the journal being made correct, the engineer cannot alter it. Under these conditions the whole area of the brass is effective in holding the journal, which increases the durability of the brass by keeping the pressure per square inch on the brass bore at a minimum.

If side chocks are used, however, it is better to set them up by wedges than by screw bolts, because from the tightness of the fit of such screws in the tapped holes, it is difficult to determine, with precision, with what degree of pressure the chocks are forced against the journal. Furthermore, the screws may not fit with an equal degree of tightness; hence, when screwed up with an equal degree of pressure, one end of the same chock may be set tighter to the journal than the other end, and any undue pressure of fit at either end tends to throw the shaft out of line as well as inducing undue wear. But when wedges are used to set up the side chocks the nuts operating those wedges may be an easy fit without fear of their becoming loosened (as set-screws in the line of thrust are apt to do).

On the fast engines of the Pennsylvania Railroad solid bronze boxes, without brasses, are used, and when the boxes require truing from having cut or from having worn oval they close them under a steam hammer, closing the bore across and enabling it to be trued out in the lathe without taking much metal out of the crown of the bore. The wedges and adjusting shoes are thickened when this becomes necessary by reason of the box closure or width.

If a brass bore does not bed fully and equally over the entire intended bearing area the part not fitting will at first perform no duty as bearing area, and the whole strain will be thrown upon a less area than is intended by the construction, causing undue abrasion until the brass bore has what is termed worn down to a bearing. The amount of this wearing down to a bearing may be so small as to be scarcely perceptible to ordinary observation, but if the oil that has passed through the journal be smeared upon stiff white paper, as writing paper, it will be found to contain the particles of abraded metal, which will be plainly distinguishable. Under these conditions the journal will have a dull, though perhaps a smooth appearance, and will not have that mirror-like surface which is characteristic of a properly fitted and smooth working bearing, while under a magnifying glass the journal will show a series of fine rings or wearing marks. It is necessary, therefore, that each brass be properly fitted to its journal so that it shall bed fairly and evenly over all the area of its bore that is intended to bear upon the journal.

The most expeditious method of fitting a new bearing box or brass to its journal is to first file the bore until it fits the journal when simply placed thereon by hand, and without going to the trouble to put the brass or the journal in position in the frame which holds them. So soon, however, as the crown of the brass beds to the journal along its whole length, the brass should be placed in its box, or in the frame, and the journal adjusted in its place and rotated so as to leave its bearing marks upon the brass bore, to assist which it may have a faint coat of red marking on its surface. The fitting should be continued both with file and scraper until the whole area of the part intended to bed fits well and is smooth and polished. To produce this result the finishing should be done with a very smooth half-round file, draw-filing so as to leave the marks in a line with the circumference of the bore, and finally with a half round scraper, which will remove the file marks. The degree of contact should be such that, when the bearing is bolted up, brass and brass, as it is termed (which means that the joint faces of the brasses are held firmly together), the journal will rotate as freely as when the top brass is removed, while the contact marks on the top brass have been removed by scraping. By this means the fit will be just sufficient to permit the lubricating oil to pass between the journal and the bearing, and the journal will work freely and easily without any play, knock, or pound. If, when the top brass or bearing is bolted home and the shaft is rotated by hand, that brass on removal shows contact marks on its bore, although it may rotate comparatively easily it will be so tight a fit that the oil cannot pass, and as a result the wear, instead of producing a glossy surface, will produce a dull one, and undue abrasion will ensue even though no rings appear.

When brasses are held in rods that connect two journals together the fitting of the brass bore must be conducted with a view to have the brasses fit their journals all over the intended bearing area of their bores, which can only be accomplished by trying the brass bores to their journals while in the rod, in the manner to be hereafter described with reference to connecting rods and to lining engines.

When a journal is worn in rings, or so rough as to cause destructive abrasion and undue friction, it may be refitted as follows:--First, with a smooth file draw-file the journal in the direction of its length, taking off all the projecting rings. Then sweep a very smooth file that is somewhat worn (which will cut smoother than a sharp file) around the circumference of the journal so that the file marks will be in the plane of revolution. Then wrap a piece of fine and somewhat worn emery paper around the journal, and wrap around it (say twice around) a piece of coarse string, leaving the two ends about two feet long. Take one end of the string in each hand and pull first one end and then the other, causing the emery paper to revolve around the journal and smooth it.

To refit the bearings, first with a smooth half-round file remove the rings or rough surface, and then fit the surface with the file, so that when in its place the journal is rotated the contact marks show a proper bearing. Then draw-file the bore with a smooth half-round file and finish with a half-round scraper, easing away the high spots until the bore shows proper contact and is smooth. A piece of fine emery paper may then be wrapped around a half-round file and the surface smoothed with the emery paper moved across the bore and not in the direction of the circumference of the same. The emery paper should be well worn for the finishing and of a fine grade number, so as to leave a bright polish and not dull marks.

In some practice the bores of brasses are left rough-filed, the file marks being lengthways of the bearing of bore. If the journal requires smoothing it is draw-filed lengthways of the journal. The philosophy of this is, that the file marks will hold the oil and afford unusually free lubrication while the bearing and journal are wearing down to a bearing.

But where the framework holding the bearings and journals are rigid, these bearings and journals may, with care, be fitted to a polished and equal bearing, leaving a smoother surface than that produced by wearing down to a bearing. But if, as in the case of a locomotive, the framework is subject to torsion, rough surfaces left to adjust themselves are possibly better than those accurately fitted, because the whole framework holding the bearings changes its form when the full load is upon it and after put to work, and the fitting done when there was no load upon the parts is no longer quite correct. The lubrication of the bearing, however, should be very free, and the effort appears at present to be to afford more ample oil ways than hitherto even at some sacrifice of bearing area.

LEAD-LINED JOURNAL BEARINGS.--If a journal is worn in grooves or undulations it becomes impracticable to properly fit the brass to it without reducing its diameter to remove the rings, and to obviate the cutting and heating which necessarily follow, as well as to obviate the necessity of fitting the brasses at all, Mr. D. A. Hopkins introduced lead-lined bearings; the lead lining being merely auxiliary to the bearing proper, which is made preferably of hard bronze, and to which the thin layer or facing of lead is firmly attached by a soldering process, so that the two metals are virtually one piece. Into this lead facing the journal, under the pressure of the car, moulds or imbeds itself from the start, and afterwards gradually wears its way through it into the hard metal. The perfect fit thus secured under all conditions of the journal, aided with proper lubrication, not only prevents heating, but secures the full wear of the brasses, and makes them at all times perfect counterparts of the journal surfaces.

Fig. 2483 shows at the top an unfitted bearing without the lead lining, resting upon a worn and badly-cut journal, the only points of contact being near the ends. For obvious reasons such a journal is sure to run hot.

The engraving below shows the application of the lead lining to the same journal, the dark shading between the journal and bearing representing the lead which has been pressed into the worn and hollow surface of the journal, forming a complete bearing and distributing the weight equally upon its surface.

Fig. 2484 represents an end view of an unfitted journal and the same lead lined.

The lead compresses until the brass meets the journal and thus permits between the two contact over the area that does fit or touch; while the lead fills the remaining area of the brass bore, giving it a bearing on the journal, thus relieving the touching points from receiving the whole weight of the load, and preventing the cutting or abrasion that would otherwise occur. As, however, the wear takes place the lead compresses, permitting the journal and brass to come into bearing over its full area, being obviously effective providing the bearing be kept free from grit, which would imbed in the bearing and cause it to unduly wear the journal.

If a brass is too tight a fit upon its journal, heating and abrasion, or "cutting" as it is termed, ensues. But if a brass or box does not fit close to its journal, lost motion and sometimes knocking or pounding ensues. When the joint faces of brasses abut, or come brass and brass as it is termed, they should be a proper fit to the journal when they are keyed, or otherwise set up close together; hence there is no danger of either having a pound in the brass, or of heating and cutting. The objection to this plan is that the brasses must be removed from their boxes and the joint faces filed away to let the brasses together, to take up the wear; hence, in positions in which it is difficult to get the brasses out, the joints should be left open, while in all cases where they can be readily removed they should be made brass and brass.

It is to be observed that brasses that come brass and brass require less adjusting and last longer than those left open, because the latter often suffer from the abrasion due to an improper adjustment.

In brasses that are left open, it is not an uncommon practice to adjust the fit as follows: Between the brass joint faces at each of the four corners a piece of lead wire is inserted; the brasses are keyed as close home as can be upon the journals, which compresses the lead wire; the top brass is then released until the piece of lead wire can be moved freely between the brass joints.

A compromise between the brass and brass and the open joint is sometimes effected by the insertion of slips, as shown in Fig. 2485 at A, B. These slips may be taken out by simply removing the top brass, while their reduction of thickness lets the brasses together to take up the wear. The thickness for these strips may be readily obtained by means of the pieces of lead wire used as already described.

In the case of large brasses which come brass and brass, much of the filing on the joint faces to let them together may be saved by reducing their thickness and area by cutting away part of the metal, as at A A in Fig. 2486.

To enable the removal of bearings for renewal, or to refit them without taking the shaft out, various forms of construction are employed, of which Fig. 2487, which shows a main bearing, is an example.

Thus, when the cap is removed the side chocks, or gibs as they are sometimes called, can be lifted out by eye-bolts screwed into the holes at _c_; the weight of the shaft can then be sustained while the bottom piece D is removed.

A great deal of trouble in fitting journals and bearings may be avoided if the best conditions are observed in their manufacture. If, for example, the conditions of casting are uniform, and the diameter of the bearing bore and journal bores are constant, that is to say, when a great number of pieces are to be bored, the amount the bearings will close across the joint being definitely determined, the conditions of boring may be made such as to allow for the closure, and the fitting in this respect may be facilitated; but this applies to small bores only, as, say, three inches and less in diameter, because in larger diameters there will be sufficient variation in the amounts of contraction across the joint face to render it necessary to fit to some extent at least the bores to their journals.

In some cases slips of paper are placed between the joint faces of the bearings, or if the joint faces do not meet, slips of brass may be placed between them; or again the conditions of chucking or holding the bearings to bore them may be such as to hold them a certain amount farther apart than they will require to be when on the journal. The bore is then made sufficiently larger than the diameter of the journal that it will be as nearly as possible round after being removed from the boring machine, and will bed down fairly upon the journal without being fitted with a file, which saves considerable labor. But unless the bearings are so held as to be to some extent self-adjusting for alignment, there is liability of the axis of the bore not being quite true with the axis of the journal, the amount being so small as to escape detection save by trial for fit with the shaft, and the bearings in their respective positions. It is a difficult matter, in the absence of special holding devices, to chuck a bearing, especially if a long one, so true in a boring machine or lathe as to insure that its bore shall stand in absolutely correct alignment with the journal when placed in its position in the framing where it is to operate, and it is for this reason that many bearings are bored while in their frames. In some cases, however, this difficulty is overcome by so constructing the bores and the pieces holding them that the boxes may swivel and adjust themselves, as in the case of the bearings of line shafting.

Examples of the oil cavities for bearings are given as follows:--

For journals of small diameter oil cups screwing into the bearing cups, with feed-regulating devices, are generally used, and the same are used in the case of two half-brasses. But if the journals are of large diameter, as, say, 5 inches or more, oil receptacles are often cast in the caps.

In the absence of side chocks in the bearing all the oiling usually proceeds from the top, save perhaps that an oil groove may be provided in the crown of the bottom brass.

Fig. 2488 represents a bearing lubricated from the top and bottom; thus in the cap is an oil cup or cavity from which passes nearly down to the bearing a brass tube containing cotton wick, which slowly feeds the oil to the bearing.

Fig. 2489 represents this tube and wick removed from the bearing. This plan of feeding is largely used on marine engines and on locomotives. When used upon stationary bearings the cotton wick need not fill the tube, but if used on reciprocating parts it should fill so that the oil may not spill over and pass too freely down the tube. In either case, however, it is desirable to twist in the cotton a piece of fine copper wire, and bend the ends over the top of the tube to keep the wick in place in the tube.

The bottom of the bearing, Fig. 2488, is provided with an oil cavity and a similar tube and wick. Usually, however, the oil is fed in at the top only, except in the case of locomotives, because in them all the weight falls on the top brass; hence, the bottom may be utilised as an oil receptacle. In English locomotive practice this receptacle as a rule merely catches the oil that has passed through the bearing box, but sometimes a roller is inserted and forced against the journal by springs so as to rotate, by friction, with the rotating journal.

The bottom of the roller runs in oil so that the roller feeds the journal with oil, but ceases to feed when the journal ceases to rotate, an advantage not possessed by self-feeding oil cups, or by the cotton wick syphons shown in Fig. 2489.

The oil ways or oil grooves are usually provided in small journal brasses as follows:--

It is obvious that if the joint faces of the brasses are left open and oil be supplied to one brass only, a great part of the oil supplied will pass out between the joint faces before reaching the other brass, and one brass will therefore be better lubricated than the other, unless each brass be lubricated independently. Even in this event, however, a great part of the lubricating material will be lost from finding rapid egress through the opening of the brasses. This may be to some extent prevented in brasses whose joint faces lie horizontally by chamfering the edges of the bore so as to form a trough extending nearly to the ends of the brass, as shown in Fig. 2492. Now it is obvious that the oil hole must always be above the journal or bearing bore; hence when the joint faces stand horizontal, the oil hole should come through the crown of the brass, and oil grooves are necessary to convey and distribute the oil along the bore. A single groove, as in Fig. 2490, is sufficient for light duty, but for heavy duty a double groove, such as shown in Fig. 2491, is necessary.

When, however, the joint faces stand vertically and come brass and brass, the oil hole may be filed half in the joint face of each brass, and the edges chamfered off as in Figs. 2492 and 2493, A B representing the chamfers and C the oil hole, the two brasses put together appearing as shown in section in Fig. 2493.

This plan has the advantage that the oil is confined within the journal, except in so far as it may in time work through the ends of the journal bore, while there are two oil grooves provided without reducing the bearing or bedding area of the brass. When the oil grooves run diagonally, as in Fig. 2491, there is the advantage that the length is greater, and lying nearer to the plane of rotation the oil flows along the grooves easier, being assisted by its frictional contact with the journal, but on the other hand the bearing area of the brass on the journal is so much the more reduced.

Oil holes that are not provided with oil cups should be provided with small wooden plugs, which will serve to keep the dirt and dust out; they should be made of as small diameter as the quantity and nature of the lubricant to pass through them will admit of, and should be left plain at the top and not countersunk, because the countersinking simply forms a dish that will collect dust, &c., which the oil applied will carry down into the bearing.

In some cases there is provided an oil dish around the oil hole, and this dish is filled with tallow that will not melt under the normal temperature at which the brass is supposed to operate. But if from defective oil lubrication or other cause the bearing begins to heat, the tallow will melt, and flowing through the oil hole afford the needed lubrication.

It is to be observed that the lubrication of a bearing in which the pressure is moved alternately from one half of the bearing to the other is far easier to attain, and more perfect, than in one in which the direction of the journal pressure is constant, because in the latter case the journal pressure acts to squeeze out and exclude the oil continuously, whereas when the pressure is relieved alternately on each brass, the oil has an opportunity to pass back between the relieved surfaces. Again the lubrication is more perfect when the direction of the journal motion is periodically reversed, as the passage of the oil through the bearing is retarded by the motion, and yet again the abrasion is reduced because, as stated when referring to rotating radial surfaces, the particles of metal abraded add themselves together and form cutting pieces when the motion is continuous in one direction, whereas in a reversing motion the particles are kept separated and flow out more freely with the oil that passes through the journal.

If a shaft having a continuous direction of rotation be given end play so that while rotating it may move endwise, the particles abraded are again kept separated, and the conditions of lubrication are such as to give a minimum of wear, because the formation of fine rings or serration is avoided, the end motion serving to cause the wear to smooth the surfaces.

When a shaft has a collar, that is subject to end pressure, the oil way may be carried up the face of the collar as in Fig. 2494 at B. So also where very free lubrication is required, an oil groove may also be cut in the journal itself, as at C in the figure. This plan is adopted by some American engineers upon the crank pins of steam engines, the grooves being cut on diametrally opposite sides of the pin in a line with the throw of the crank.

Referring now to the oil itself, it is generally conceded that a pure sperm or lard oil is equal to any that can be used for general journal lubrication, but the ordinary purchaser has no means of knowing if the oil is pure. The requirements of an oil for lubricating purposes are given in the following paper on testing the value of lubricants, which was read by Mr. W. H. Bailey before the Manchester (England) Institution of Employers, Foremen and Draughtsmen:--

"A fact in connection with oil and lubrication is probably about as difficult a thing to describe as anything which agitates the minds of engineers and mechanical men. We appear to have very little published information on the subject, except that which describes the labors of Morin, of France, about forty years ago, and that which has been given to us by Professor Rankine more recently in this country. Those investigators who preceded Morin do not appear to have published information of very much value, or which can be used with profit for the discussion of lubricants, for their researches have been more concerning the proportions of bearings, and the value of different materials of construction, rather than the value of different lubricants.

"At the present moment so little is known generally concerning the performance of different oils, that the public are much at the mercy of the vendors of these oils, who can make almost any assertion they like without fear of contradiction.

"The valuable discoveries of our distinguished townsman, Dr. Joule, have enabled us to look upon the cost of friction and the cash value of heat as mere questions of arithmetic. Dr. Joule's investigations have been put into such forcible and elegant English by Professor Tyndall, and other students of the science of force, as to cause us to understand that when friction is produced heat is lost, and that all energy thus wasted passes away in this heat, which may be measured and valued with nearly as much facility as any article of commerce. We may gather from this knowledge, when we apply it to workshop economy, that if a pedestal or bearing becomes so hot through friction as to cause 1 lb. of water to be raised only one degree Fahrenheit in temperature in one minute, that heat has been lost equal to that which would be created by a weight of _one pound falling through a space of 772 feet_. We are told that if we apply this conversely, that heat has been lost which would lift 1 lb. weight 772 feet; and if we apply these illustrations still further, and imagine forty-two pedestals or bearings losing heat by friction in a similar manner, we may inform ourselves that we are losing nearly 1 horse-power, because they represent 32,424 foot-pounds of force; and if we know from our books what our coal costs, it will take very little trouble to give us the exact cash value of this friction and destructive action.

"What is friction? It may be described as the effect produced by two bodies sliding one upon the other, which have upon their opposing surfaces minute asperities, which interlock with each other. The sliding movement which forcibly removes these minute irregularities creates what we call friction. Friction is reduced when these asperities are small, and lubrication is resorted to to prevent that loss of power caused by motion under these conditions. The chief lubricants used are oil and tallow, which have a less coefficient of friction than the parts in contact. It may be well now to state that the term 'coefficient of friction' is an expression which indicates the proportion which resistance to sliding bears to the force which presses the surfaces together. There is little friction when this amounts to only one-twentieth, it is moderate when it is one-tenth, and it is very high when it is a quarter or twenty-five per cent. of the force which presses the surfaces, together, as I before said.