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 required doming of tungsten contact points on levers to accommodate for potential mis-alignment.
| Identifier | ExFiles\Box 35\6\ scan 171 | |
| Date | 1st May 1926 | |
| Contd. -2- EFC2/113.5.26. points on the levers are apparently slightly domed as a natural result of the grinding, and the average amount of doming on these levers is about the amount that was required on the points to accommodate perfectly flat surfaces on the levrs. It will readily be understood by the suppliers that since the behaviour of tungsten contacts depends on current density, it is very necessary to have just the right compromise in allowing for mis-alignment to prevent in the one extreme case of perfectly flat surfaces, a point contact entirely on the edge, and in the other extreme case of excessively domed surfaces a point contact taking place nearly in the centre. Therefore, it is clear that the right amount of doming is that amount and no more which will prevent the point of contact of the otherwise flat surfaces being shifted right to the edge due to a want of alignment of 3 or 4°. Then the moment the contacts begin to work, they will immediately begin to bed more nearly over the central portion of the surface than on the edge, whereas in the case of the excessively domed surfaces, the contact surfaces would probably get spoilt and badly oxidised before they had a chance of bedding over a larger area. We return the screw contacts herewith and in the meanwhile we are retaining the levrs which we will duly have nickel plated and fitted with rubbing blocks so that they will be in readiness upon the receipt of the screw points. | ||