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).
The coefficient of friction for steering ball pads with test data and proposed improvements to finishing procedures.
| Identifier | ExFiles\Box 95\1\ scan0408 | |
| Date | 19th May 1937 | |
| -2- (3) Measurement of the coefficient of friction between the ball and the pad indicate that this falls by a very large amount as the surfaces become run-in, and this, we believe, is the case of the trouble experienced in service. Typical figures are given below of the spring load necessary to give the required friction torque, 3 lbs. at the length of the cross steering tube (25 ins.), for various conditions of the pad. Condition of pad Spring Load -lbs. New pad lapped in with grinding paste as now assembled on Production. 180 Ditto after 10 mins. running in by hand. 330 Similar pad after 10,000 miles running on road. 415 New pad finished by hand reaming with spherical ended rose cutter. 320 The above figures indicate that some method of running in the ball pads prior to final assembly on the chassis is desirable and that finishing by reaming is preferable to lapping. The springs at present fitted are satisfactory up to a load of 250 lbs. but at this point go choc-a-bloc. We have run springs to Rm.{William Robotham - Chief Engineer}254 for 20,000 miles on 35-X. and we suggest that these should be standardised immediately and used for all replacements. In order to improve on the present position regarding the loss of friction with running in we suggest that the following procedure should be adopted. (1) If Production find that the material of the ball pads (BZ/PC) is not too hard for hand reaming, that they should finish in this way in preference to lapping. (2) That a final burnishing operation should be adopted on the upper pad G.84934. This cannot yet be done on the lower pad as this is not pressed into its housing until a late stage on the Production line and further operations would probably delay the chassis. The adjustable cross steering tubes which will be run on 32-EX., will overcome this difficulty. (3) That the joints should be set to a friction load of 3 1/2 lbs. when assembled on the chassis. continued | ||