Bearing (mechanics)

“ Roller and Ball Bearings.—If rollers are placed between two surfaces having relative tangential motion the frictional resistance to be overcome is the small resistance to rolling. The rollers move along with a velocity equal to one half the relative velocity of the surfaces. This way of reducing frictional resistance has been applied to all kinds of mechanical contrivances, including bearings for shafts, railway axle boxes, and axle boxes for tramcars. An example of a roller bearing for a line shaft is illustrated in figs. ”

“ The balls, in the ordinary bearings in the market, roll upon conical, spherical, or cylindrical surfaces. In either of the last two cases the radius of curvature of the box is so much greater than that of the ball that the effect is the same as upon the cone, and in all cases where a bearing is well constructed the action is the same as that of a ball rolling upon a flat surface. True, some friction results from the contact of the balls with each other, but as there is no force driving them together, it is very slight. ”

“ Bearings In the general meaning of the term, a bearing is any part that carries weight or pressure and at the same time rubs over another surface. According to this definition, the portion of the cylinder walls traversed by the pistons are bearings, and that is in reality the case, but the term has come to be applied more specifically to the part of the machine in which another part revolves, either continuously or intermittently. Thus the portions of the crank shaft on which it is supported and the parts of metal in which they revolve combine to form the crank shaft bearings. ”

“ Wheelwrights of old soon found that a wheel need not be solid, that strong spokes, a sound rim, and a metal tire embody the utmost strength and lightness. Roller and ball bearings much extend the benefits of simple wheels; they lessen friction in the best typewriters, bicycles, and elevators; in wagons, carriages, and automobiles roller bearings are so helpful that their use should be universal. Of notable efficiency is the Hyatt bearing, formed by winding a steel strip into a spiral roller. ”

“ If a belt is put on too tight, it may pull so hard on the bearings as to heat and cause them to cut. It is easier not to put the belt on too tight at first and to relace it several times while it is stretching, than it is to repair a rough bearing. ”

“ 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 ”

“ In the advanced stage which bicycle construction has reached to-day there are a large number of ball-bearings in a machine—in fact, there are balls wherever there is friction, however light. These bearings should have careful adjustment. Perhaps a glance at the sketch of a wheel bearing will make the construction clearer. Of course the bearings of different makes of wheels vary, but the principle is the same in all. The little steel balls are the only medium by which the weight on the bearing is transmitted between the rim and the cone (hub and axle) . ”

“ The screw itself must rest in bearings, and the end motion be prevented by a point bearing against its fiat end, which is protected by hardened steel or a flat diamond. Collar bearings introduce periodic errors. The secret of success is so to design the nut and its connexions as to eliminate all adjustments of the screw and indeed all imperfect workmanship. The connexion must also be such as to give means of correcting any residual periodic errors or errors of run which may be introduced in the mountings or by the wear of the machine. ”

“ 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. ”

“ In this case the metal is used in a thin layer, and serves only, as it were, to fill out the small interstices caused by wear on the axle and bearing, the latter being usually made of some rather easily fusible alloy of lead and tin. Such bearings are very durable, but expensive, and can only be used for large machines. For small machines, running gently and uniformly, white-metal bearings are preferred, and do excellent work, if the axle is not too heavily loaded. ”

“ A worn main bearing can be detected by placing the metal end of a screw-driver or hammer on the crank-case opposite the bearing and the other end to the ear. If the bearing is loose or worn a dull bump or thud will be heard. This looseness should be taken up by removing a shim of the proper thickness.
Fig. 9. Cam Shaft
Main bearings run loose for any length of time will be found very hard to adjust as the jar which they are subjected to invariably pounds them off center which makes readjustment a very difficult task to accomplish with lasting effect. ”

“ To facilitate the making of ground and scraped joints it is preferable that the surface of the joint, both on the cylinder and the cover, project from the rest of the flange, from the bolt holes to the bore in the one case, and from the bolt holes to the body in the cover in the other, so that the bearing surface of the joint shall extend from the inside edge of the bolt holes to the cylinder bore only. ”

“ General Notes on Lubrication. No matter how carefully the surface of a shaft or bearing may be finished, there always remains a slight roughness or burr of metal, which although of microscopic proportions is productive of friction or wear. Each minute projection of metal on a dry shaft acts exactly as a lathe tool, when the shaft revolves in cutting a groove in the stationary bearing. ”

“ When properly lubricated, an iron or steel shaft will run in almost any kind of a metal bearing that is sufficiently strong to carry the weights and pressures imposed upon the shaft. The friction generated between two different metals that rub against each other, however, varies according to the composition of those metals, and consequently it is advisable to employ some material for a bearing that will offer a minimum resistance to the turning of the46 shaft. ”

“ All faults and all strikes that do not coincide very closely with one of those four lines of bearing are either small and unimportant, or occupy spaces that may be described as merely the connecting links where the one line of bearing is passing into the other. ”

“ Trunnion bearing, for oscillating cylinders, &c. The steam is conveyed through the bearing, which has a stuffing box and gland to prevent leakage.
830 & 832. Swinging support for a shaft, having a sliding bevil gear or other motion upon it which has to pass the swinging support; used for lathe sliding gear, overhead travellers, &c.
831. Ball and socket centre for car bogies, &c.
833. Pedestal with side adjustment for the brasses by taper keys and screw adjustments.
Bearings running under water are generally lined with strips of lignum vitæ and require no lubricant. ”

“ The shaft cannot be cut by this set screw as it bears on the split hub.
CYLINDER HEAD BEARING AND CAP
The shafts are steel, fitted with Woodruff Keys and Phosphor Bronze Bushes with Collars, which make the bearings self-oiling and practically free from wear. Heavy tin is used in the construction of the Cylinders which are carefully balanced and thoroughly tested.
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TWIST GEARING
Simplicity and convenience characterize our Ring Spinning Frame gearing. All gears are cut. They are of ample width, run quietly and are well boxed to prevent accidents. ”

“ Ever stop to count up how many bearings there are about your car? If you haven’t, you are likely to lose your bearings while you hunt for the several hundred bearing points of the modern automobile.
A bearing is a support for a moving member, so designed as to minimize friction and receive wear, and to permit of fine adjustment. ”

“ A rounded bearing two inches wide is cut in the axle beyond the spokes so as to correspond with the other end, and beyond this the axle is left square. Bearings for this wheel are made in the edge of a stout plank notched as shown at B, and held in place by iron straps as also depicted at B. Long screws or screw-bolts, commonly known as lag-screws, will hold the strap in place, and from the square end of the shaft the connection is made for power. ”

“ The upper pivot, or bearing is made of tempered steel wire and of sufficiently small diameter to be quite flexible in the length between the top of the brass shaft and the guide ring in which it rotates. ”

“ With oil the friction appears to be a minimum when the pressure on the surface of a bearing is about 90 lbs. per square inch. The friction from too small a surface increases twice as rapidly as the friction from too large a surface, added to which, the bearing, when the surface is too small, wears rapidly away. ”

“ The wheels of a skip are fixed on the axles, which run in journal boxes, thus insuring smoother running [Pg 18] than is obtained with loose wheels. The details of the journal bearings, as shown in Fig. 15, consist of three castings, the bracket a, which is bolted or riveted to the gunboat, a pivot casting b, and the bearing proper c. The bearing c rests on the axle and carries, by means of trunnions d, the pivot casting b, on the top of which is placed a rubber cushion e to lessen the shocks between the casting and the bracket.
Fig. 14
Fig. ”

“ In girder-work generally, and more particularly in plate-girders, considerable latitude obtains in the amount of bearing allowed. Clearly, the surface over which the pressure [3] is distributed should be sufficiently ample to avoid overloading and possible crushing or fracture of bedstones where these exist; but if no knuckles are introduced, this is an extremely difficult matter to insure. A long bearing may deliver the load at the extreme end of the surface on which it rests, or, more probably, near the face. ”

“ Thus the projected area of the surfaces of a journal 6 in. in diameter and 8 in. long is 48 sq. in., and if the total load carried by the bearing is 20,000 pounds, the bearing would be said to carry a load of 417 pounds per square inch. When a shaft rotates in a bearing continuously in one direction the load per square inch with which it is safe to load the bearing in order to avoid undue heating is much less than if the motion is intermittent. ”

“ Similarly in adjusting the main bearing boxes to the crank shaft, either the nuts, or what are called leads, may be taken to adjust the fit. Leads are necessary when the joint faces of the brasses do not meet, but are left open so that the wear can be taken up while the engine is running. ”

“ Fig. 143 shows a type of double row ball bearings. Ball bearings are being used more extensively each year by the manufacturers of light and heavy duty motor vehicles. The efficient reliability and ease of action has proven to be the main factor in the development of this type of bearing. One of the big features in considering ball bearings is that a ball rolls equally well in any direction, and the slightest effort [239] will start it to rolling. It is a proven fact, that a ball is started more easily than any other type of supportive element. ”

“ There are others that are difficult of access—as in the case of bearings of screw-propeller shafts. Serious mischief may result before the heating of the bearing proclaims its dangerous condition. In some cases the timber work is set on fire, which may result in serious consequences.
In order to remove the cause of such serious mischief, I designed an arrangement of bearing, which enabled it, and the shaft working in it, to mutually accommodate themselves to each other under all circumstances, and thus to avoid the danger of a want of due and mutual parallelism in their respective axes. ”

“ In a horizontal bearing d is a shaft at whose end is a weighted lever l, and on the end of this shaft is a crank pin shown engaging a sleeve e which affords journal bearing to the outer end of shaft c, so that operating the weighted lever l operates e, and therefore shaft c with the spur gear receiving motion from the worm. ”

“ Top half of right bearing is formed by rocker arm, right, which extends back and carries angle of site scale, pointer, rack, and level and forms a bearing for elevating handwheel shaft. Rear of rocker arm, right, is braced by rocker arm brace, a diagonal hollow rod attached to rocker arm and rocker. Top half of left bearing is formed by rocker arm, left, a diagonal arm extending upward to the rear to form a support for sight. Movement of the angle of site mechanism is limited in elevation by the rocker stop bolted to the side of the rocker and in depression by a screw in the arc. ”

“ Each ball of the same bearing must be made of exactly the same size as its companions—or at least within one or two ten-thousandths of an inch—and each one must be large enough and of sufficient strength to withstand, by itself, the entire pressure in that bearing. The inner ring slips over the bearing portion of the shaft with a comparatively tight55 fit, while the outer ring remains stationary in its bed in the crank case. ”

“ A wood wheel with a V-shaped groove on its edge is nailed to the larger end of the cylinder. The hole in the core is fitted with a brass tube, driven in tightly to serve as a bearing. A rod that will fit the brass tube, not too tightly, but which will not wobble loose, is threaded and turned into the upper end of the support. The core with its attached driving wheel is shown in Fig. 3. The dotted lines show the brass bearing and rod axle. The end of the axle should be provided with a thread over which a washer and nut are placed, to keep the core from coming off in turning. ”