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).
Analysis of a steering failure on a 25/30 HP model due to fractured ball bearings and proposed design modifications.
| Identifier | ExFiles\Box 106\3\ scan0374 | |
| Date | 21th May 1936 | |
| To K.{Mr Kilner} c. to Wor.{Arthur Wormald - General Works Manager} c. to Hy.{Tom Haldenby - Plant Engineer} c. to Ds. c. to EV.{Ivan Evernden - coachwork} X530 HS{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}9/JH. 21.5.36. 25/30 H.P. Steering. We have just had a failure on the standard type steering on 21-G-IV after a mileage of only 2000. The failure consisted of fracture of one of the C.250 balls in the bearings of the roller follower and made itself apparent by heavy steering and crunching noises from the gear. This failure is serious as the parts in question are identical to present production. From an examination of the detail drawings of the inner race and the roller follower, we find that the radius of the bearing tracks is 0.187" for a 0.125 radius ball. It would seem that this is excessive as usual ball bearing practice for heavy loads is for the track radius to be from 3% to 4% greater than the ball radius. It would also seem to be advisable to specify the angle of contact, which, we agree with the design dept., should be 45°. If we reduce the radius of the tracks to the correct figure of 0.130 the need for accuracy in grinding them becomes very much greater than it is at present and it is doubtful whether either the Adamant Engineering Co., or ourselves will be able to maintain the accuracy. In order to overcome this difficulty it has been suggested that the final grinding of the inner and outer tracks should be done by a ball bearing manufacturer so that responsibility for the bearing rests with one manufacturer instead of three as at present. We are in agreement with this, and will get into touch with Messrs. Ransome & Marles in order to obtain some bearings finished by them as soon as possible. In the meantime we suggest that, in order to maintain continuity of production, we should produce the parts in question as at present but with the altered dimensions and should inspect these dimensions very carefully. | ||