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).
Examination of Wraith III Unit No.1 timing gears to investigate the cause of a whine.
| Identifier | ExFiles\Box 136\1\ scan0211 | |
| Date | 14th June 1937 | |
| To Rm.{William Robotham - Chief Engineer} 1155/ 14.6.37 WRAITH III. TIMING GEARS. UNIT NO.1. An examination of the above gears for cause of whine gave the following:- Crank pinion to camwheel. Bedding good. Alignment of axes and helix angle not checked. Camwheel to Dynamo Pinion. Very bad bedding on drive side of teeth. Bedding to rear of dynamo gear all the way round. Measurement of skewness of axes gave error of 0.00125" in width of gear. The direction of this skewness would, however, with perfect gears give a bedding to the front of the gears. It therefore followed that the helix angles of the two gears must differ by more than 0.00125" in the width. A rough check of this difference of angle confirmed that it existed and gave approximately 0.002" in the width of the gear. We attribute the gear whine to the large error in helix angle. In order to obtain gears which are quiet as first assembled, the out of alignment between gear axes should not exceed 0.00025" in the width of the gear. The maximum error obtained on Production 25/30 and Bentley crankcases is 0.0004". It should be possible to control the helix angle to 0.00025" in the width of thegear. Wraith III.No.1.Unit is therefore a particularly bad example of manufacturing errors as the crankcase error is 5 times what it should be and the gear helix error about 8 times. It should be emphasised that it is the skew error of the axes rather than varying centre distance, which is important. So far as we are aware this skew error is not measured during inspection. Also Inspection have no satisfactory method of measuring helix angle. Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} | ||