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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).
Technical memorandum on achieving silent gearing in timing and gearbox systems.

Identifier  ExFiles\Box 136\5\  scan0308
Date  31th August 1937
  
RHD
E.S.
W.A/Mr.Ashby.
C.Hms.
O.Rm.{William Robotham - Chief Engineer}
G.{Mr Griffiths - Chief Accountant / Mr Gnapp} NY/GS.

F.J. HARDY

Any comments?

1152

SILENT GEARING.

Referring to "timing" and "gear box" gears, there are certain points which are essential in order to obtain the necessary smoothness, and consequent quietness, in action.-

(a). Accurately ground gears with a fine surface finish.

(b). Accurately produced helices by using a gear train to give exactly the helix called for. In order to avoid the delay entailed in obtaining special gears we are arranging where practicable to modify the helix to the nearest existing train - this may occasionally entail special cutters, but since the gears are finally ground, exactness in the cutter size and shape is not absolutely necessary. In future the D.O. will arrange to make the centres to suit existing trains.

(c). In order to avoid the necessity to cut with a sufficient clearance to overcome the tendency to gear tooth "hum" or "sing" a number of possibilities exist. The general principle of attaining this end is, to produce a form of tooth correction, which whilst giving a close fit on the pitch line will permit clearance on the gear tooth tips, but to a certain strictly controlled extent, which will still allow the tip to carry load but to a reduced amount. The way that this can be attained on a "generating" type of machine is, on the gear which controls the pair, or in timing gears "the train"; to produce a gear with a tooth form suitable for a gear with a less number of teeth than that on the gear to be produced, this will result in slightly clearing the tip and flank of the mating gear or gears, and can be achieved by mounting the gear to be ground on a hub eccentric to the gear by the amount to give the correction. The gear will rock
  
  


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