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 bedding of electrical contact points, discussing doming and the use of platinum.
| Identifier | ExFiles\Box 35\6\ scan 291 | |
| Date | 5th July 1927 | |
| EFC2/T5.7.27. -4- Contd. Only two were bedding centrally; one of these shewed 50% bedding contact. The other four were bedding about 50% of the total surface on the sides of the points. We are including in our production tests an instruction for the better electrical bedding of the points before passing to test. (At present they are lined up by the Test Dept. before despatch), but we think that this is not an entirely satisfactory procedure in view of the possible replacement of the points, but there would appear to be a certain amount of justification for the doming, this doming to be the minimum amount possible, i.e. .001" of centre above circumference. The objection to doming may be that initial bedding over a small area may not satisfactorily spread before a hollow and mound are formed, and subsequent contact takes place between the sides of the hollow and the mound (see samples). The same phenomenon of course takes place with flat points which do not bed together correctly initially, and even may take place with those which do reasonably bed. A suggestion is that in view of the uni-directional current, better running time would be obtained if we had twice the depth of platinum on the screw point that we have on the lever point. In all our tests with the current in the present standard direction, the platinum is not consumed from the lever point to any extent at all. It would appear necessary only to have a sufficient minimum amount to form a base. On the screw point, however, owing to the formation of a depression Contd. | ||