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).
Investigation into crankshaft manufacturing, forging costs, design difficulties, and potential improvements.
| Identifier | ExFiles\Box 148\5\ scan0214 | |
| Date | 12th November 1937 | |
| To Rm.{William Robotham - Chief Engineer} From RHC{R. H. Coverley - Production Engineer}/SB.{Mr Bull/Mr Bannister} c. to Sg.{Arthur F. Sidgreaves - MD} HS.{Lord Ernest Hives - Chair} c. to By.{R.W. Bailey - Chief Engineer} Da.{Bernard Day - Chassis Design} c. to Roy.{Sir Henry Royce} HS{Lord Ernest Hives - Chair}/IS. CRANKSHAFTS. Investigation has been made into the manufacture of Rolls-Royce Chassis crankshafts with the object of ascertaining the extent to which Forging Cost could be reduced by simplified design and alternative materials, also to discover whether our forgings are supplied at an economical price. Three firms were visited in connection with the matter, English Steel Corporation of Sheffield who supply all Rolls-Royce Production Chassis Forgings, Ambrose Shardlow and Co. of Sheffield, and Smith Clayton & Co. of Lincoln who supply certain Experimental Crankshaft Forgings in small quantities. At each of the above firms the same manufacturing difficulties were put forward and it is therefore proposed to deal first with Design, as it affects Forgings. The Design of 25/30 HP. Crankshaft is not particularly difficult for forging apart from troubles inseparable from most seven bearing crankshafts, and could not be improved without re-designing the engine. The distance between the sides of adjacent crankpin webs being short, necessitates narrow projections on the Die which wear badly and sometimes break away completely. Since the inception of the original 20 HP. Chassis the crankshaft design has become gradually worse from the Die aspect due to wider webs, shorter crankpins, harder material, etc. The life of the Die materially affects the cost of Forgings because after the initial payment of part Die cost with the first forging order, die maintenance and replacement becomes the manufacturers responsibility and is naturally allowed for in the original forging quotation. The possibility of forging the crankshaft to finished size and machining only the pins and journals has been considered, but this could not be introduced with the present 25/30 HP. or Wraith engine without completely re-designing due to existing thin crank webs which would be very much weakened with a forging 'draw' or angle on either side. Final balance is obtained by grinding the profile of the webs where necessary, and if it were attempted to leave the webs in a forged condition the appearance would become irregular where the surface had been ground for balance. | ||