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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).
Investigation into gear and pinion running issues, including bedding, lapping, and backlash problems.

Identifier  ExFiles\Box 136\1\  scan0105
Date  24th October 1933
  
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Hs{Lord Ernest Hives - Chair}/P.H.7/KT. 24.10.33.

the axis about which the teeth were cut and lapped. This is shewn in Fig. 2.

Eccentric running of the gear or lack of parallelism in the crankcase cannot cause the above bedding.

The pinion complete with its shaft was removed from the engine and set up between centres. Attempts were then made to detect the errors by means of a clock reading to 0.001" but were unsuccessful, so that the errors were evidently smaller than could be measured by the method adopted.

A plain bearing was fitted in place of the ball bearing in order to eliminate cause (3) mentioned above. The results were no different.

The pump pinion which had been made for Unit E.6. was tried on Unit E.7., but with no improvement - i.e. the bedding was the same as Fig.1.

The original pinion was then tried on a new pinion shaft, but the results were as before. This can be assumed to prove that cause (2) does not apply.

The pump pinion and idler were removed from the engine and fitted up on the lapping rig for further lapping. The marking obtained on the rig was similar to that obtained on the engine. The lapping was not continued long enough to correct the errors in the gear, so that when put back on the engine there was little or no improvement.

A set of gears was fitted to the engine which had not been hardened or lapped, but was left as cut by the gear cutting machine. This set of gears was very noisy indeed, probably because the gears were oversize and had no backlash. They were removed and lapped to reduce the tooth thickness. The lapping was not continued long enough to produce perfect bedding, and when tried on the engine were still bad although they had sufficient backlash.

The pump pinion was again a bad offender but in this case the bedding was hard on the back of the pinion all the way round of the circumference as shewn in Fig.3.

The possible causes of this are :-

(a) Pump pinion axis not parallel with idler axis on engine.
  
  


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