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-office memo discussing the manufacturing processes and improvements for LaSalle transmission gears.
| Identifier | ExFiles\Box 170\2\ img265 | |
| Date | 10th April 1935 | |
| CADILLAC MOTOR CAR COMPANY INTER-ORGANIZATION LETTERS ONLY DATE 4-10-35 TO Mr. W. Olley ADDRESS FROM E.{Mr Elliott - Chief Engineer} R.{Sir Henry Royce} Ryland ADDRESS SUBJECT Processing LaSalle Transmission Gears. All gears are hobbed in one cut except 15 tooth counter gear which is a double width face gear driving the idler and sliding low gear. This 15 tooth gear is rough and finish out on a Fellows Gear Shaper. Since this gear has been changed from 45° helix angle to 30° a shaving operation has been found to be very helpful. This is done on a "Michigan Tool Co." machine (Detroit). All gears except 15 tooth counter gears are ground on Pratt & Whitney Gear Grinders, and then all of them are lapped by the "Inco" process. The "Inco" lap is made from C.I., which is poured around a master steel gear for a core. This casting is then ground all over except tooth faces. The lap is then mounted in the "Inco" lapping machine, which strokes the work up and down in the lap while a radial load is applied to the lap, thus operating on one face of the teeth; reversing the radial load on the lap brings the other face of teeth in contact with lap. The work is controlled for helix angle by a lead screw or helix guide in the machine. It requires from 15 to 20 gears, each being lapped a short time, to bring the lap into shape for regular production use, and is good for an average production of 50 to 60 gears. In the early stages of LaSalle Transmission production the contacts as practiced in the Cadillac were imitated. However, this was far from satisfactory especially under coasting conditions in second and low gear. Improvement in gear sound was definitely noticeable as tooth contacts were made fuller on the tooth faces. This is explained by the fact that LaSalle gear faces are from 1/4" to 5/16" narrower than the Cadillac gears, thereby resulting in less overlap control by the helix, and requiring more involute contact to offset this loss. Present production practice is holding contacts within a very close range. The contacts must be full or just showing a shaded sign of heavier contact an addendum of driving teeth and dedendum of driven teeth. The "Inco lapping System" is not as satisfactory as hoped for when put in use on LaSalle gears. This, however, I believe is largely due to narrow tooth faces. Our Methods Engineers are now experimenting with the Michigan Tool Co.'s Gear Lapping Machine. This machine has three large cast iron gears, - friction loaded, and driven by the work gear, which also oscillates slowly across the lapping gears. In practice one of the three lapping gears is run on a different pitch center than the other two. This is done to eliminate some of the tendency of lapping above and below the pitch line. Some success has been experienced to date. Twenty-five more sets will be tried. | ||