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).
Modifications to dynamo brushes, specifically the radius and chamfer, to prevent chipping.
| Identifier | ExFiles\Box 50\5\ Scan336 | |
| Date | 14th July 1924 | |
| To BY. {R.W. Bailey - Chief Engineer} from EPC. c. BY {R.W. Bailey - Chief Engineer} /RD. c. Wor {Arthur Wormald - General Works Manager} /Mr. Brock. X4333 EFC {E. Fowler Clarke - Electrical Engineer} 3/T14.7.24. (Handwritten) X4637 X.9670 X 4333 RE BRUSHES. Reference your BY12/H8.7.24. we agree that it would be a definite advantage for the radius of the working surface of the brush to be slightly greater in the first instance than the exact radius of the commutator, so that if everything is correct, initial bedding takes place across the central zone of that area, and if the angle of the brush holder is slightly incorrect, this would not result in the chipping of the brush due to the corner dropping down into the slots. At the same time we do not see the desirability of the .030" chamfer which you suggest, as this in any case will only be there for the initial portion of the running, and may mean that the accurate setting of the dynamo, in the first instance, with the narrower (effective brushes, for the required output subsequently when this portion of the brush has worn away, is slightly inferior. This might not be serious and no doubt experiment would settle the point definitely. If there is any tendency to chip originally, apart from the very initial bedding, then there would still be this tendency when the chamfer has disappeared with wear. As stated, we do not see any real advantage in the addition of the chamfer, whereas we entirely agree with the increased radius in the first instance. You will remember that it is now specially stated in our production test that before the dynamo is sent out, the brushes must be bedded right across their working surfaces circumferentially over a longitudinal distance of at least so much. This initial circumference would be lessened by the additional chamfer. Another thing is that we have found very little actual wear to take place with the dynamo running but not generating, in fact far the more important effect appears to be due to the tearing action of the current. We agree that it would be a distinct advantage to have a rig for 'running in' brushes in the first instance of a diameter slightly larger than the commutator Contd. | ||