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).
Cost analysis memo comparing different crankshaft designs, including those from Oldsmobile, Jaguar, and Wraith.
| Identifier | ExFiles\Box 132\1\ scan0029 | |
| Date | 19th January 1938 | |
| 1116 also Policy. RHC.{R. H. Coverley - Production Engineer} from Rm.{William Robotham - Chief Engineer} c. Ey. c. Hs.{Lord Ernest Hives - Chair} Rm{William Robotham - Chief Engineer}3/R.19.1.38. CRANKSHAFTS. -> See Policy We have read with interest RHC{R. H. Coverley - Production Engineer}/SB{Mr Bull/Mr Bannister}1/MC.17.1.38. The basic point we were after in submitting the Oldsmobile shaft for cost analysis was - "Is a four-bearing crank fundamentally very much cheaper than a 7-bearing crank when both are treated in the same manner", i.e., one must not compare a drilled shaft fitted with oilers and machined all over with one that has not these refinements. The tabulated figures show that the lowest figure at which we think we can produce an Olds. shaft (3½-litre engine) is £8/18/-. We know the cost of the 3½-litre Jaguar 7-bearing shaft, both forging and machining, and this is appreciably less than £8. Therefore we are satisfied that we have not been extravagant in incorporating a 7-bearing shaft in the new engine which is being designed. What we have got to learn is how to get down to the Jaguar figures for the same article. Incidentally, the dimensions of the Jaguar Shaft have been referred to several times as being appreciably less than ours, but in fact we understand that both the dia. and length of the pins and journals are the same as the Wraith, though the overall length of the shaft is some 10% less, which is presumably saved on the webs and front or rear bearing, i.e., we shall be content if our final costs get within 10% of theirs. However, the shaft should be available for examination almost immediately. We note on the tabulated cost figures that the figure for the Wraith forging in V.C.M. is still given as £6/-/-, as it was in RHC{R. H. Coverley - Production Engineer}/SB{Mr Bull/Mr Bannister}1/MJ.12.11.37. for a forging weighing 140 lbs. If, as seems possible from your memo, the new forging weight for the same shaft, less test piece, is round about 110 lbs, and the material cost is as previously, i.e. 10.3d per lb, then the saving in forging costs over the present Bentley shafts would potentially appear to be about 30/-. We note that you are pressing E.S.C. on this point, and find it difficult to understand how they can argue against a reduction in cost. Rm.{William Robotham - Chief Engineer} | ||