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).
Design, testing, and cost-effectiveness of a banjo tube rear axle for the Wraith model.
Identifier | ExFiles\Box 7\3\ X 602 Axle Rear-page22 | |
Date | 24th September 1936 | |
Ha/Gry.{Shadwell Grylls}16/KW.24.9.36. Rear Axle Construction. The Wraith rear axle has been designed with a banjo tube made on the Scott principle. The object of this departure from the usual R.R. arrangement is to save cost. The saving in cost expected of about £5 per car is almost entirely due to the fact that we would be able to obtain the Scott tubes, unmachined, at £1 each, whereas the total cost of our present axle tubes is £6. 8. 0d. The sample Scott tube supplied by Rubery Owen proved on test that it would take a large permanent set if the car were jacked up under the axle centre. Later tests with an additional stiffening plate weighing 6 lbs. reduced the set to .020 at 5500 lbs., which in our opinion is still unsatisfactory. We have therefore gone into the question of the most suitable design for a rear axle, and for this purpose have visited Fords, Rovers, Rubery Owens and Ransome & Marles to discover how a cheap rear axle can be made satisfactory. It is an obvious conclusion that if the material of a Scott tube is adequate then our present axle tubes could be made cheaper than a Scott tube in that material. The setting of the gears in a banjo axle is no cheaper than now. There is therefore no saving in cost attributable to the word "banjo" but without any doubt an increase in weight, large if a Scott type and smaller if of welded construction. Rubery Owen tell us that they could not make a banjo to G.W.552 in less than 7/32" material at the centre, weighing a further 6 lbs., in order to leave sufficient at the ends for our machining requirements. Rovers reject about 25% of the banjos supplied owing to inaccuracy of the ends. Admitting therefore that the Scott construction is not suitable, we went into the price of an axle to the same drawing made in two halves, welded top and bottom. To G.W.552 this would cost in .4 carbon steel £2. 15. 0d. and with integral ends to G.W.553, £3. 5. 0d. plus £400 tool cost. | ||