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 from Hoffmann Manufacturing Co. Ltd. discussing bearing choices and thrust loads for a 40/50 chassis bevel pinion.
| Identifier | ExFiles\Box 49\1\ Scan363 | |
| Date | 14th July 1921 | |
| R.R. 199 (250T) (SD676 19-7-17) MP:80866 COPY. THE HOFFMANN MANUFACTURING CO, LTD., CHELMSFORD. July 14/21. Messrs. Rolls Royce Ltd., DERBY. Dear Sirs., Your Ref: BY1-P12721. For the attention of Mr R.W.Harvey Bailey. We are in receipt of yours of the 8th inst., with regard to the application of a 365 Journal Bearing to the Bevel Pinion of your 40/50 chassis. Unfortunately you do not mention the speed of this spiral bevel so that we are unable to make any concrete comparisons with regard to the loads mentioned, but as a safe estimate, we think you might reckon with your conditions upon this bearing being capable of withstanding an end load equal to one third of its normal journal rating. Thus its sum total under the dual conditions would be one third thrust and two thirds journal. Its listed capacity at 1,000 r.p.m. is 3,300 lbs. Our experience so far with regard to spiral bevels, which has been obtained on very much smaller cars than the one you mention, has exposed the fact that the actual thrust developed by this type gear is rather larger than is given by the theoretical formula, and under these circumstances we have always found it necessary to fit a Double Thrust Bearing for this duty. Another difficulty presented by the use of one Ball Journal for the reverse thrust and a Single Thrust Washer for the forward thrust is the difficulty in adjusting the two without imposing initial thrust on the Journal Bearing. You will appreciate that this has to be exact, as should the adjustment be too tight the journal bearing will fail from end thrust, whilst should it be too slack there is the possibility of trouble with the spiral gears owing to slight lateral movement of the bevel pinion. Before definitely deciding this matter, we think it would be to your interest to make a practical test, p.t.o. | ||