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).
Analysis of gearbox failures concerning 2nd speed dog teeth and a review of gear tooth correction and strength calculations.
| Identifier | ExFiles\Box 136\2\ scan0328 | |
| Date | 1st May 1941 | |
| -2- Cont'd.{John DeLooze - Company Secretary} obvious from the photograph. Remedy - Strengthened 2nd. speed dogs. Chassis 30.G.VII. Gearboxes 10.B.V. (47,634 miles) and K.8 B.F. (11,820 miles). The 10.B.V. gearbox was reported on in Ev{Ivan Evernden - coachwork}/Tln.5/JH.17.9.40. In the K.8.B.F. box 2nd. speed dog teeth have broken off. These have not done as well as the previous dogs on this car. The differences are that EX.34153 were straight sided dogs for experimental production reasons GB.5126 are involute sided, Fellows cut, teeth. Dimensionally they should be very similar. It looks possible that the depth of case was too much on GB.5126. - Remedy - Strengthened 2nd. speed dog teeth. For the 8 cyl. torque we definitely need improved 1st. speed teeth, 2nd. speed dogs, and layshaft bearings. All these have been designed, and two of these three we are obtaining on the replacement boxes now being built. It is unfortunate that, for production reasons, we are not getting strengthened 2nd. speed dogs on these boxes. The E.2.B.1. 1st. speed failure suggests that with .035 correction the wheel tooth has less root strength than the pinion. The tooth layouts prepared by Rm{William Robotham - Chief Engineer}/HH. confirm this, and indicate that whilst .035 correction gives good tooth action it results in a wheel tooth with only 85% of the strength of the pinion tooth, allowing for the difference in gear and pinion widths. The proportions of 7.2 D.P. and 8 D.P. teeth were based on these 9 D.P. .035 corrected teeth, and are as follows :- 9 D.P. teeth .035" correction = 31 1/2% corrn. 8 D.P. teeth .0375" " = 30% corrn. 7.2 D.P. teeth .040" " = 28.8% corrn. For equal root strengths, we should have 9 D.P. .018" correction = 16% corrn. 8 D.P. .020" Correction = 16% 7.2 D.P. .025" correction = 18% | ||