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 tooth design, profile errors, and pressure angles, referencing the Phantom III constant mesh pinion.
| Identifier | ExFiles\Box 136\5\ scan0314 | |
| Date | 9th September 1937 | |
| -2- HHC/Mer.1/Fh.S.9.57. is in sympathy with the offending member of the pair. (e) The effect of errors in pressure angle, providing that good bedding of teeth is obtained, appear to give a minimum of trouble, but good mating of profiles is essential. Profile errors, obtained from the varying grinding loads on badly distorted gear, are responsible for the majority of high frequency notes and easily distinguished from the coarseness of poor surface finish. In future design of gears, it is suggested that the maximum of root clearance to be given to teeth to allow the slight flat (dressed upon the wheel to aid in smooth finish) to operate below the base circle, and the radius which is generated will be well below the working depth. An example of this condition has occurred on U82925, the Phantom III constant mesh pinion, in which case several hobbing modifications were made to aid distortion difficulties, and resulted in the necessity of large stock removal from the root diameter. The efforts to reduce grinding load and give sufficient working depth, were considerably restricted, but although this defect has temporarily been overcome until such times as a modified hob is available, the margin of clearance is small. The suggestions put forward under item (e) in memo' EY.6/G.13.8.37. and the figures stated in memo' EY.6/S.1.9.37. Whilst we agree with the theory of such suggestions, it is considered that their practical application cannot easily be adopted to the machines of the generating type. It may be considered that the application of an eccentric base circle block would achieve this object, but it must be considered that though the arc of contact for both the bands are equal, the change in normal angle to the base block would vary the tension in the bands. It may be also considered that it would eliminate the splitting of distortion errors, which is now achieved by adjustment of base circle angular movement relative to grinding wheels (provision for this is inherent) in the machines design). The adjustment of the machine heads to a modified pressure angle, results in a theoretical error in the bed grinding angle of the machine, as the basic calculations obtained from a machine constant of 15° pressure angle. Attempts in this direction to allow the tap relief have been unsuccessful on Wraith gears where a modified pressure angle was attempted in grinding. -Cont'd- | ||