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).
Gear design, referencing Almen's 1937 paper on transmission gears and subsequent developments.
| Identifier | ExFiles\Box 178\2\ img048 | |
| Date | 12th March 1940 | |
| Serial No 21 Rm{William Robotham - Chief Engineer} page 2 2) Drummond of National Broach, is at work with rights to get the gear grinding out of their system. He says the actual bedding errors, lack of parallelism under load, etc., which they are using successfully on their engines, is beyond the range of ordinary accepted practice in automobile work on unground gears. So we shall watch this development with interest. 3) I have been reading Almen's paper (enclosed) of September-October 1937 on transmission gears and talking to him about it. The conclusions he reaches in this paper are not clear. For instance, the fatigue chart of figure 3, using the McMullen-Hurban method of calculation, appealed to me, because it has already proved successful on axle gears and it divides the transmission gears into two groups, as shown by the lines I have sketched in. Almen rejects this chart because the two groups divide themselves on a basis of helix angle, not material or finish. He wants to find a working formula from which a designer can predict life with the confidence now used on axle gears. He is not concerned with any of the theoretical arguments but only with the results. This is why he prefers the Logme formula shown in figure 1. Ever since this paper was published, the divisions have been concentrating on getting rid of the terrific scatter of the results pointed out by Almen. It appears that the successful one has been George Rothrock, gear engineer at Cadillac. Almen tells me this morning that George has just completed a series of tests showing greater uniformity and getting rid of the end bedding, which, as pointed out in figure 2, ruined the results before. He has done this by an entirely new attack on the subject of shaving all teeth to give, not the theoretical helix, but anti-helices which will be flattest under load, and a slight barrel lapped into the teeth on a three gear rotary lapper. The barrel is essential in any case to get central bedding. Uniform heat-treat and quenching methods have also been developed to get as nearly as possible uniform wind or unwind of the gears in quenching. Steel used is still 4615 case hardened. As a result of this work Almen says that the fatigue line of his charts of 1937 have certainly gone up. Drummond points out that 'straight' spurs introduce the | ||