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).
Inter-organization letter detailing production methods for making Cadillac transmission gears.
| Identifier | ExFiles\Box 170\2\ img267 | |
| Date | 2nd April 1935 | |
| CADILLAC MOTOR CAR COMPANY INTER-ORGANIZATION LETTERS ONLY DATE April 2, 1935 TO Mr. E.{Mr Elliott - Chief Engineer} W. Seaholm ADDRESS FROM E.{Mr Elliott - Chief Engineer} R.{Sir Henry Royce} Hyland ADDRESS SUBJECT Mr. W. A.{Mr Adams} Robotham's Letter to K.{Mr Kilner} Olley, March 6, 1935. In order to fully answer Mr. Robotham's questions and observations, it is necessary to give a detailed description of our production methods for making Cadillac transmission gears, which is as follows. Two types of gear grinding machines are used. The one rolls the gear by a stationary revolving grinding wheel (Lees Bradner, Cleveland, Ohio), the other rolls the gear by a grinding wheel which strokes back and forth the length of the gear tooth, (Pratt & Whitney, Hartford, Conn.). The Pratt & Whitney machine is the better for fast work and maintaining tooth form on a production basis, but does not produce such a good surface finish. The surface is very much like that obtained by hobbing whereas the Lees Bradner machine produces a finish much like that obtained from a gear shaper (Fellows). Their latest two wheeled machine is intended to overcome this undesirable feature. From the very first experimental helical ground gears we learned that it was undesirable to match mating gears which were both ground on the Pratt & Whitney machine, and that pairs ground on the Lees Bradner or a Lees Bradner ground gear and a Pratt & Whitney ground gear made a better combination, particularly after lapping. Therefore, counter gears are ground on the Pratt & Whitney and mating gears on the Lees Bradner. Gears for the Cadillac car are ground with approximately a five minute minus pressure angle on the driving teeth and a five minute plus pressure angle on the driven teeth. Mating gears are then set in a lathe having a pair of parallel centers mounted on the cross slide. The cross slide is adjusted so gears run almost metal to metal, and a generous quantity of lapping compound applied for about one to one and one half minutes of rotation in each direction at approximately 200 R.P.M. of driving gears. During rotation the lathe carriage is slowly moved back and forth dwelling slightly at each end (1/4 inch over lap). This operation due to the greater sliding action above and below the pitch line of the gears causes the bearing of the tooth to come down on the driving teeth and up on the driven teeth. In other words, it tends to cancel the difference in pressure angle which has been ground into the gears. The tips of the driving teeth | ||