Q. What is the difference between a ball and roller bearing and which has the most friction?

A. In either ball or roller bearings the effect of the load is to flatten the supporting members a very small amount so that in a roller bearing the contact between the roll and the raceway may be represented by a rectangle having a length equal to the roll but a width so small that it is usually considered a line contact. In a ball bearing the flattening of the ball produces an ellipse of such small area that it is usually considered a point of contact. As the

Fig. 237.-Parts of Typical Single Row Ball Bearing.

reduction of friction depends upon the amount of surface in contact it can be readily understood that the form having the least amount of contact would have less friction than the other though its capacity would also be lower than that of a roll of equal diameter but having contact along the entire length. Ball bearings are generally employed where it is desirable to reduce friction to a minimum and where bearings must attain high speed. Roller bearings have been widely applied where bearings of relatively small diameter but of large carrying capacity must be used, where the shafts revolve at

comparatively low speed and where maximum bearing efficiency is not important.

Q. Name important parts of any anti-friction bearing.

A. The important parts of an anti-friction bearing of the roller form are shown at Fig. 236-B, while those of ball bearings of the radial and double row types are outlined at Figs. 237 and 238. The principal parts are an inner race, a number of supporting antifriction or rolling elements, a suitable cage or separator to contain them and an outer race to act as path for the rolls or balls.

or rollers. This intro- Fig. 238.-Important Components of Double duces an undesirable

element of friction,

Row Ball Bearing.

due to the rubbing of one revolving member against its neighbor, so most anti-friction bearing designers provide a cage, container or separator, that is depended on to separate the rolls or balls from each other.

Q. What are separators made from?

A. The design of the separator and the function it is intended to perform determine the materials to be used in its construction. A cage or retainer that is depended on to carry the balls or rolls and not to actually keep them separated from each other may be made of stamped steel while those forms that are intended to separate and guide rolling members usually pocket them in an oil filled individual chamber for each member and are generally die cast of bronze or white metal.

Fig. 239.-Front Hub of Ford Model T Mounted on Cup and Cone Type Ball Bearings.

Q. What other function besides separating the balls or rolls must the separator perform in a "take down" bearing?

A. In a bearing of the cup and cone or taper roller type the separator also acts as a retainer to prevent the rolling elements coming out of place if the bearing is taken apart.

Q. Are annular radial type ball and roller bearings adjustable for wear?

A. Annular ball bearings having vertical load lines and roller bearings having straight rolls are not adjustable for wear.

Q. How is the factor of deterioration made negligible in annular bearings?

A. Annular bearings of the non-adjustable type are very accurately constructed and are made of material having a high elastic limit and great strength. As there is but little friction between the highly finished, accurately machined and fitted parts of a well made annular bearing there will be practically no wear and if the bearing is not overloaded and is properly lubricated the factor of depreciation will be negligible.

Fig. 240.-Front Hub With Timken Roller Bearings.

Q. What advantages have "take-up" bearings over the straight radial type, and wherein are the latter superior to the former?

A. When cup and cone ball bearings as outlined in a front hub at Fig. 239 or tapered roller bearings as shown at Fig. 240 are used it is possible to take up any looseness existing between the parts by screwing up on an adjusting nut that will bring the cone or inner member closer to the outer member which effectively eliminates lost

motion. Bearings of this type may be easily removed for inspection and can always be adjusted by an experienced person so they will turn with minimum friction and with absolutely no lost motion. When used in front hubs in the manner indicated the combination of the two bearings which have diverging load lines from the center produces a hub mounting capable of withstanding end thrust from either direction and support a radial load as well. Bearings of the straight radial type would not be suited for this application

Fig. 241.-Gearbox With Shafts Mounted on Roller Bearings.

unless supplemented by forms capable of taking end thrust. A disadvantage of some moment sometimes advanced against the adjustable form of anti-friction bearings is that these may be adjusted too tightly or not tight enough by an inexperienced mechanician or novice motorist and the bearings be subjected to shocks and stresses that they were not designed to withstand, the result would be rapid depreciation and considerable friction at a point where this should properly be eliminated. When using annular non-adjustable forms of bearings these are received from the specializing