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).
Manufacturing process and interference fit specifications for aluminium brake drums.
| Identifier | ExFiles\Box 85\1\ scan0217 | |
| Date | 19th October 1936 | |
| x206 To By.{R.W. Bailey - Chief Engineer} c. to EHC. c. to Sft.{Mr Swift} Hs{Lord Ernest Hives - Chair}/AFM.{Anthony F. Martindale}26/KW.19.10.36. Aluminium Brake Drums. Wraith has been designed with aluminium brake drums; and Bentley 6-B-IV has run 15,000 miles with these drums fitted, and the drums are intact and still run true. Therefore the works will shortly be called upon to produce such drums. It is absolutely essential that the interference fit between drums and liners shall be that called for, because if it is too low the liners come loose, and if it is too high it becomes very difficult to get the liners into the drums, as there is a limit (200°C) to the temperature to which the aluminium cases may be raised during the shrinking-in process without damaging them. On Bentley the interference fit is to be between 0.028" and 0.030"; i.e., there is a limit of .002" of machining both liner and drum if normal production methods are used. It is obviously quite impossible for the works to keep to this limit and there is no reason why they should, provided that assembly is selective. All that is necessary is that the total interference should be within the stated limits. The best way to produce these drums seems to be as follows :- Machining of liners and aluminium cases must take place in batches of not less than 100. The bigger the batch, the better. (100 drums corresponds to 50 cars). After machining each case and liner must be measured up, the case on one diameter, the liner on four diameters. The case must have its internal diameter written on the inside of the end plate in indelible pencil. The average outside diameter of the liner should be written on the inside of the liner (which is then only rough machined) also in indelible pencil. | ||