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).
Letter discussing gear design alternatives, including helix angles, gear ratios, and rockershaft dimensions.
| Identifier | ExFiles\Box 28\2\ Scan185 | |
| Date | 20th May 1933 | |
| Messrs. Rolls-Royce Ltd. Contd 2. 20.5.33. We think perhaps you will readily appreciate this point if you will imagine a rockershaft and follower being at an angle of 44½° from the vertical, and engaging in the Cam track. We have worked out the approximate size of a gear made to give a ratio 16 to 1 in the box, and a helix angle of approximately 16½°, which helix angle has been found to be the most satisfactory from your tests. With this helix angle, together with a 1" diameter inner tube, and the same diameter Cam as shewn on the "J" Gear, a rockershaft would be required having the distance from the centre line of the shaft to the centre line of the Follower equal to approximately 2.9/16". This length is very nearly as big as the 2 7/8" provided in the "O" Gear rockershaft, and the gear generally would not be very much smaller than the "O" Gear. Further, in view of the fact that the "O" Gears is a standard gear of ours and made in quite large quantities, and that the alternative gear with 2.9/16" rockershaft would be a special, and would naturally be made in small quantities, the special gear would undoubtedly come out more expensive in manufacture than the "O" Gear. Reviewing the whole situation, therefore, it would seem that on the assumption that a helix angle of 8° 45 mins would not be suitable, that there are 3 alternatives available. 1). To cut down the lock of the car by using a shorter drop arm. 2). By using a higher gear ratio than the gear raio aimed at, viz. 16 to 1. 3). By using "O" Type standard gear. We trust that the contents of the above letter will be found to be clear to you, and we shall look forward to hearing further from you when you have had an opportunity of considering the same. In regard to the Drop Arms, we note that you are sending these to us, and we would add that one has already arrived, this being - 2 - | ||