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transmission main shaft. As a thrust load is present at this point, in the gearbox shown at Fig. 241 the rear end of the shaft is supported by a pair of tapered roller bearings while at Fig. 242 one double row ball-bearing performs the same function.

Ring Gean

Drive Pinion

7Ball Bearing

Double Row
Ball Bearings

Fig. 243.—Differential and Driving Gear Assembly Supported by Ball

Bearings.

Q. At what point is considerable thrust present?

A. Considerable end thrust in addition to radial load is present at the front wheels of an automobile, at the worm or bevel driving gearing and at the rear wheels.

Q. What types of bearings are suited for these points?
A. As previously explained bearings adapted to resist end thrust

and radial load should be used at all points where the load is really an angular resultant of radial and thrust components.

The bevel gear drive and differential assembly shown at Fig. 243 is mounted on double row ball-bearings which are capable of taking loads from all directions. These are used to support the differential casings to which the ring gear is attached as well as to take the main thrust load back of the bevel drive pinion.

Two forms of rear wheels are shown at Fig. 244, that at A is the hub of a wire wheel for pleasure car service in which the load is carried by ball-bearings of the adjustable cup and cone pattern. The heavy truck wheel outlined at B is mounted on a combination of single and double row bearings. The double row member is clamped so it takes the major part of the radial load and all of the thrust. The single row bearing, which is restrained only at the inner race, takes radial stresses solely.

Q. Can a radial ball bearing take thrust, and how much?

A. While the regular single row annular bearing having a vertical load line is not recommended to take end thrust it is capable of successfully resisting end thrust equivalent to 25% of its radial capacity.

Q. Name the three important American roller bearings and describe them.

A. Three roller bearings developed in America, where the perfection of this form of bearing has been carried to a fine point, are the Timken, Hyatt, and Bower. All other forms are practically modifications of these three main types. The Timken roller bearing is a form employing tapered rollers which we have previously described, the Hyatt uses the flexible plain rollers, while the Bower employs a straight roller with an upturned locating flange. The taper roller can take end thrust and radial load while the flexible roller is suited only for radial stresses.

Q. What is the conventional method of installing anti-friction bearing inner members?

A. The inner races of anti-friction bearings are usually machined so closely to standard sizes that various makes will interchange without difficulty. The shafts to which these races are fitted should

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed]

Fig. 244.-Outlining Two Methods of Applying Ball Bearings to Rear Hubs.

be machined with equal accuracy and should be just enough smaller than the bearing bore so that inner race will be an easy push fit on the shaft. It is customary to always restrain the bearing inner race from movement by means of a clamp nut or its equivalent. These are depended on to force the inner race firmly against a shoulder or tubular spacing member on the shaft, as outlined at Fig. 245.

Q. How are anti-friction bearing outer races secured?

A. If a bearing is to resist end thrust as well as radial load it is customary to clamp the outer race between a threaded closure member and a shoulder in the housing as shown at Fig. 245. The closure member, however, does not bear against the bearing outer race but a space of about .01 inch is allowed between the bearing outer race and shoulders on clamp nut and housing. An outer race is invariably a free push fit in the housing. If the bearing is to be subjected to only a radial load it is not necessary to clamp the bearing outer race.

Q. Why is it desirable to clamp bearing inner race to shaft?

A. The bearing inner races are clamped firmly to the shaft in order to prevent creeping of the inner race on the shaft under heavy loads as this would tend to wear the shaft and the bearing would not be held in place as firmly as it should be if the cone once started to turn around.

Q. When narrow single row bearings are to be housed in soft metal, what is a desirable precaution to take?

A. In order to prevent the narrow outer races, which are of hard steel, from peening the soft aluminum alloy of a gear case, for example, it is customary to house the outer races in a member of pressed steel, cast bronze or malleable iron 'which is firmly pressed into the soft metal case and which takes all the strain imposed on heavily loaded bearings.

Q. What is the best method of installing radial bearings when two are used on a shaft subjected to thrust?

A. Only one of the bearings should be employed to resist the thrust load and this should have both inner and outer races clamped. The other bearing which is depended on to take only radial loads has a "floating' outer race but a clamped inner member.

Q. In assembling adjustable ball or roller bearings what precaution is necessary?

A. It is imperative that the parts of the bearing be adjusted to a nicety. The adjusting nut should be screwed up only to such

[graphic]

Fig. 245.—Method of Mounting Ball Bearing Subjected to Radial and

Thrust Loads.

a point that absolutely all the lost motion or radial play is taken from the member supported and yet that member should be free to revolve without friction. If the bearings are tightened up unduly they will wedge and bind and wear out quickly. If they are not adjusted tightly enough the balls or rolls will be subjected to a series of hammer-like blows whenever the bearing is operated and this will also produce rapid depreciation of the bearing.

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