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).
Standardizing the numbering and specifications for vehicle springs, focusing on piece numbers, lubrication, and poundage.
| Identifier | ExFiles\Box 154a\4\ scan0018 | |
| Date | 15th December 1936 | |
| -2- Rm{William Robotham - Chief Engineer}/Les.2/AP.15.12.36. The Piece Number. A spring made to the same drawing, but varying in 50 lbs. from another spring is given a different "Piece No.". In the case of the 30 HP. rear springs, a variation of 100 lbs. has a new "Piece No.". There is no separate drawing for Piece Nos., but on the main spring drawing particulars of plate thicknesses are given from information received from the manufacturers. The attached list shews the plate thicknesses of four production springs. The figures in red are the corresponding plate thicknesses taken from the drawing. It can be seen that the manufacturers do not (and would not be reasonable to expect them to) work to the drawing plate thicknesses owing to the variations in rolling of the spring plates. It is very hard to identify a spring Piece Number by measuring the thicknesses of the plates. The Piece Number is no benefit to the manufacturer who has to mark it on every spring, but it often causes confusion when quoted instead of the Drawing Number. We recommend that the Piece Number is deleted, but a maximum thickness of any plate in the spring is given on the drawing in order to limit the maximum stress. Lubrication Number. The particulars of the spring lubrication should be given on the spring drawing. A different type of lubrication should have a new Drawing Number. Type in Lbs. This is the poundage which corresponds to each Piece Number. e.g. a 1336 actual poundage spring is a "type 1350 lbs." Springs are ordered by the Drawing Number and the type. For the 30 HP. rears where types vary in 100 lbs., intermediate poundages are ordered by stating 'plus' or 'minus' after the "type". Springs can be produced within a limit of ± 15 lbs. from the poundage ordered, without difficulty. In order to reduce the number of springs having extreme poundages, which either eventually become obsolete due to low poundage or unsuitable for immediate production as their poundage is too high, it is best to order springs as near as possible to the average ideal poundage. e.g. If when ordering springs for a 100 chassis it is known that 1350 lbs. is the average ideal poundage, it would be more liable to involve scrap by ordering 50 pairs of 1300 lbs. and 50 pairs of 1400 lbs. than if 100 pairs of 1350 lbs. springs were ordered. continued. | ||