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).
Comparison of cost and manufacturing processes for Wraith and Bentley road springs from suppliers Firths and Woodheads.
| Identifier | ExFiles\Box 9\5\ 05-page161 | |
| Date | 10th January 1938 | |
| 646 C. Rm.{William Robotham - Chief Engineer} Les.{Ivan A. Leslie} ROAD SPRINGS. Does the cost of the Wraith & Bentley road spring compare reasonably on a cost of material & no of leaf basis. i.e. Wraith springs seem expensive. I think there is sufficient evidence available to finally settle the 'finish' of the road springs for our various chassis. When dealing with the Wraith, we arranged to order springs from both Woodheads and Firths, which were to be made up from rolled bar, without grinding or plating. In the result we found that whilst Firths had closely followed our instructions by producing springs from rolled bar, Woodheads had ground their leaves on a wet grind stone; the result of the test was that the top leaves broke on both sets of springs, and in the case of Firths the times of failure varied from 10 1/2 hours to between 20 and 30, Woodheads were between 25 and 35. The material from which Firths produced their springs was precisely the same as that delivered for all chassis up to the present, the only difference being the leaves were not ground or plated, showing that the drop in endurance which was a very serious one, was simply due to the omission of the grinding operation, which removes the decarburised surface which is present on all rolled bar. Following this, we arranged to obtain quotations again from both firms for springs where the top leaves were ground all over and plated, the secondaries were to be left unground in each case. The quotations submitted as a result of this brought the Firths and Woodheads spring prices to practically the same figure; for Bentley 111 there was a difference of 1/- in favour of Woodheads and for Wraith 1/6d. In view of these figures I then asked Messrs. Firths to quote me a price for grinding and plating all the secondary leaves of the Bentley and Wraith springs under discussion. The figures given were :- (a). For Bentley ... 2/7d. per spring. (b). For Wraith ... 6/4d. " " an increase in price which would not justify under any circumstances taking the risk of spring failures, which I am certain will occur in the secondary plates unless this further precaution is taken. The price for springs for Wraith from Firths unground was £2. 12. 7d. the addition of 6/4d. for/plating brings this price to £2. 18. 11d. | ||