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).
Technical discussion on bearing types, insulation materials like Bakelite, and component design for armatures.
| Identifier | Morton\M6\ img079 | |
| Date | 2nd April 1928 guessed | |
| (5). We have used the type of bearing referred to viz. one on a split taper sleeve, and have not had good results. We have had many failures of this type. (6). We have had the greatest success from the machines where the ball and roller bearings have been pressed on to the shafts and not easily removable. The failures seem to be caused by the maintenance engineers taking the easily removable bearings from the shaft and not replacing them with sufficient care. (7). The ideal arrangement is to cone and thread the shaft as you show in your sketch, but it is the most expensive of all, and as a general rule too expensive and people will not pay the price. It requires a first class job, both grinding and fitting. (8). We enclose a drawing of rocker bar and its details. (9). Insulation of terminals. We are using "Bakelite" Shields between terminals but we do not like "Bakelite" insulating tubes and washers. "Bakelite" will carbonise over the surface and cause breakdowns. The Mica or micanite insulation in the dirty air surrounding does not carbonise and is always preferable for use at sea. If the surface of a washer gets burnt it can be scraped clean. Bakelised paper insulation is not entirely satisfactory unless it is oil immersed, frequently failing where it is exposed to dust and moisture through its readiness to carbonise. It is the best material we know for insulation and mechanical strength in clean and dry situations or if oily. If we decided on moulded Bakelite, there would be the expense of moulding to consider. It is not our standard practice to mount terminal in the manner shown on drawing B.254 and it hardly seems worth while going to the expense of having special moulds made for something which will probably never be used again. We have also to consider the question of delivery which is urgent, and it would take some considerable time to obtain moulded Bakelite washers. The mechanical strength of moulded Bakelite is not very great, it is very brittle and rather apt to crack. (10). You will notice that the revised drawing shows the bearings carried in separate housings as you suggest, and it appears to be the best way, seeing that we have to supply spare armatures. Of course, the spare armatures would have their bearings pressed on to their shafts, and such housings would keep the journals from being damaged and free from dust and dirt. (11). Little, if any advantage is gained by using bearings the same size at both ends. If we use a roller bearing at the main end we must use a ball bearing at the commutator end. If we use a ball bearing at the commutator end of the same size as the main bearing it makes a very large diameter bearing. Thanking you for your interest in this matter, and | ||