From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter discussing the issues and costs of using special inch-size ball bearings versus standard millimetre bearings.
| Identifier | ExFiles\Box 20\7\ Scan109 | |
| Date | 27th June 1921 | |
| COPY. Oy3 - G 27621. June 27th 1921. Mr. Claude Johnson. Managing Director. Rolls-Royce Ltd., London. England. Attention:- Mr. F.H.Royce & Works Committee. Dear Sir, Re Ball Bearings. In view of the new designs coming through at Derby, we think it should be mentioned that all the Hoffmann inch-size bearings used on the present car, are special in the U.S., and cost us from 2 to 3 times the price of the standard millimetre size bearings of similar capacity. One can buy from stock in the U.S. deep-grove bearings without entrance slots, and equal in quality to Hoffmann's, from at least two makers, Hess-Bright (now SKF Industries) and the U.S.Ball Bearing Co., our present suppliers, but only in the standard millimetre sizes - light, medium and heavy, and in the original D.W.F. thin millimetre sizes; not in any inch sizes. The S.A.E. standards, to which all makers adhere, do not include the D.W.F. sizes. The S.A.E. does include however a wide series of millimetre bearings in which the width is in inches while the bore and outside diameter are the standard millimetre dimensions. These wide sizes apply to the double row bearings like those made by the New Departure Co. The S.A.E. standards also include a range of separable or magneto type bearings, in millimetres. Finally, the S.A.E. include a range of extra small journal bearings. Angular contact bearings, single row, are a developement of the magneto type, and are not separable. They are deep groove bearings with the thrust line inclined at 10° or upwards to the radial, and are increasingly used for carrying thrust particularly at speeds of 1000 r.p.m. upwards. The S.A.E. standard dimensions for these are the same as for radial bearings. To illustrate the difficulty of using inch size bearings, we have recently had one or two cases of bearing breakdown on the Lucas dynamos, and have been unable to buy replacement bearings in the whole of America, because they were inch size. | ||