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 the time, metal removal, and tool changes for drilling the Wraith versus Bentley crankcase top half.
| Identifier | ExFiles\Box 132\3\ scan0101 | |
| Date | 7th July 1938 | |
| To Ry & Rm.{William Robotham - Chief Engineer}....From RHC.{R. H. Coverley - Production Engineer} 6/6. RHC.{R. H. Coverley - Production Engineer}1/MC.7.7.38. Handwritten: Files Scott Handwritten: Mr h...s deals with this CRANKCASE TOP HALF - WRAITH The final jigs and tools for drilling the lower face of Wraith crankcase are now available, and it is found that the time required for drilling the sump, joint face (including main bearing stud holes) is twice that of Bentley, time allowances being 1 hour 50 minutes and 3 hours 40 minutes, respectively. The actual amount of metal removed from Wraith crankcase during drilling is approximately 8 cu.in. as compared with 12 cu.in. on Bentley, the position, therefore, being that although 50% less metal is removed, the cost of the operation is doubled. The following summary shows the number of tool changes involved during drilling of these faces, it being necessary in most cases to change the loose bush in the jig plate at the same time as the drill. The term "cuts" includes, drilling, reaming, c'boring, tapping and spotfacing and although certain sizes are repeated in the figure given below, the depths are different necessitating a change of tool. Wraith Crankcase EW.1768. No.of cuts. Dia. 2 .406 2 .375 2 Spotface holes.125 2 .437 2 .500 2 .650 14 .325 14 .375 14 .375 6 .275 4 .212 1 .500 1 .593 1 .625 3 .365 3 .375 1 .437 14 .324 10 .265 1 .625 Bentley Crankcase No.of cuts. Dia. 14 .324 14 .375 6 .275 7 .125 4 .265 3 .365 7 .421 8 .324 2 .406 14 .375 Total No. of Holes = 79 Total No. of Tool Changes = 10 Continued....... | ||