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).
Report comparing the maintenance requirements and costs of Marles and Worm & Nut gear systems.
| Identifier | ExFiles\Box 153\2\ scan0235 | |
| Date | 1st February 1937 | |
| -3- we do not consider that the accuracy required on the cam is exceptionally high, or that, if we made this part ourselves, we should have any difficulty in maintaining the required standard. The Worm and Nut gear requires very careful and specialised production but we know the requirements, and, apart from occasional lapses, can satisfy them. (4) Maintenance of Adjustment. The development of backlash has given some trouble on our early Marles gears, partly due to inexperience in assembly, but largely because the parts supplied by the Adamant Co. were considerably below normal standards of surface hardness. The Adamant Co. have now revised their heat treatment, and our methods of assembly are now very good. The Marles gear will probably always require slight adjustment after the first 3,000 - 10,000 miles running, and for this reason, the Wraith design embodies a very simple and rapid means of carrying it out. The Worm and Nut gear has no provision for, and does not require, adjustment. (5) Costs. Factory costs of the P.III and 25/30 Marles gears and the 20/25 or Bentley Worm and Nut gears are as below:- P.III Marles Gear £19.17.6. 25/30 " " £19.-.- 20/25 Worm & Nut Gear £16.16 - We estimate that the cost of the Wraith Marles gear will be £13. - .- The principal reasons for the high cost of the P.III and 25/30 gears are the excessive prices we pay for parts supplied by the Adamant Co., the complication of the split box, the chromium plating of the outer steering tube, and, in the case of the P.III, complicated mounting of the gear. On the Wraith gear the cam only will be obtained from the Adamant Engineering Co., the box is not split, and we have assumed that there will be less chromium plating. | ||