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).
Differences in gear design practices and the effects of the pot-lapping process.
| Identifier | ExFiles\Box 137\5\ scan0104 | |
| Date | 3rd October 1930 guessed | |
| --2-- Where the gears differ from our practice is in - (a) Lower pitch-line speeds (i.e. shafts closer together). (b) Steeper helix - 30° to 45°. (c) Wider Gears. They differ from Panhard practice in - (a) Fine pitch (12-15) instead of coarse. (R.R. practice). (b) In some boxes a center bearing. (R.R. practice). (c) In some boxes the second or third speed is placed at the rear end of the box so as to use the rear mainshaft bear- ing to take the thrust of the helical driven gear. Every helical gear is being pot-lapped (after finishing) by the Gear-Process lapper. (This of course is Mr. Dyer's interest and is why I suggest further investigation by Wor.{Arthur Wormald - General Works Manager} and Hs.{Lord Ernest Hives - Chair}) The thing the pot-lapping does is - (a) Check the accuracy of hobbing. (b) Correct the helix. (c) Correct the indexing. (Unground hobs made by Greenfield Tap and Die at Athol, Mass. to drawings of the gears to be hobbed, rather than drawings of the cutter, have been found best.) Coarse pitch and less helix angle give worse results than fine pitch and high helix angle, because the latter condition puts more emphasis on indexing and less on tooth form, and pot-lapping is most effective in correcting the indexing rather than the tooth form. With reasonably careful hobbing and one to three "cycles" of pot-lapping (a cycle being one rev. of the work) noise- rejec- tions at Studebaker have been kept down to 4% and total re- jections including final gearbox test, to 10%. Second speed is said to be "practically inaudible". Mr. Dyer stated that he considered that Speed Ratios are still not right, and the great advantage still held by the "spool" gearbox is its relative ratios in high and third. (Continued) | ||