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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).
Ball bearing fits and interference limits for 25 HP & Peregrine gearboxes.

Identifier  ExFiles\Box 104\4\  scan0167
Date  12th September 1932
  
Hdy.{William Hardy} (WW). X5310
BY.8/G.12.9.32.
(X402)

BALL BEARING FITS. 25 HP. & PEREGRINE GEARBOXES.

Referring to HDY.{William Hardy}1/M.6.9.32. the fine limit on the shaft diameter where the ball bearing is seated is not due to having to pass the/bearing over a similar sized spigot to reach its final position, it is the result of many discussions with the Works to :-

a/- Ensure a reasonable positive interference type of fit.

b/- Avoid as far as possible the upper limit, making the interference fit too great.

Hoffmanns limits for bearing and shaft are :-

a/- Bore of bearing where bore is 'b'

b + .0002
- .0003

b/- Shaft diameter where diameter is 'd'

d + .0002
+ .0007

These limits give a maximum interference fit of .001 which is much too high to permit the parts to be assembled as has to be done in our case with the parts dropped in from above and the shaft threaded through the gears and bearings.

On the other hand it is essential that we have
  
  


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