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).
Detailed description of the gear shaving machine process, including cutter specifications and tooth form generation.
| Identifier | ExFiles\Box 174\2\ img067 | |
| Date | 27th March 1937 guessed | |
| -3- (3) Shaving Machines. (see photos 4, 5 & 6). The object with the shaving machine is to produce a sliding action across the pitch line. This is done by crossing the axes of the two gears. Experience has shown that this cross should be between 10° and 17° but 3° to 30° (as covered by their patent) will work. It is vital to keep chips away from the job. To this end holes are drilled at the root of the cutter wheel and liquid is forced through these holes (parallel with the gear axis) to clean every tooth. For steel a 15% sulphur oil is used. For cast iron either compressed air or paraffin, for fibre, compressed air. They have had no demand for shaving bronze gears, but I should think it would be very good for our timing gears. Gear cutter life is from 6,000 to 10,000 gears per regrind with 6 regrinds per gear cutter. Chevrolet do not inspect the first 4,000 gears from a shaver as they say they are bound to be O.K. Gear cutter tooth form is generated by careful grinding with hand indexing and hand feeding. This they say insures the geatest accuracy. Their index plate is held to 0.0002 and the finished cutters to a pitch error of 0.0003. The departure from the true involute required (see back) is obtained by trueing the grinding wheel so that it has not quite a true rack straight side. This is done as sketched :- [DIAGRAM TEXT] KNIFE EDGE FORMER NOTE DEPARTURE FROM STRAIGHT LINE DIAMOND WHEEL WHOLE DIAMOND & MOUNTING MOVED VERTICALLY TO TRUE WHEEL The involute is generated in the gear from the rack grinding wheel. The centres on the shaving machines seemed to me very ample and the helix angle accuracies obtained were remarkable. | ||