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).
The manufacturing considerations for adopting the Widney concealed bonnet hinge.
| Identifier | ExFiles\Box 7\6\ X 605 Bonnet-page17 | |
| Date | 7th January 1938 | |
| 1026 STEADMAN hda Rm{William Robotham - Chief Engineer}/512 W/S. To Cx.{Major Len W. Cox - Advertising Manager} & De. From MEI/SS.{S. Smith} c. to Sg.{Arthur F. Sidgreaves - MD} & E.S. c. to KL. & S.S. MEI/SS.{S. Smith}1/MJ.7.1.38. WIDNEY CONCEALED BONNET HINGE. In view of the consideration given to this feature and the fact that it has been raised in Im/Std.4/HL.6.1.38 for Wraith, it is thought advisable to put forward various points affecting its adoption from the Manufacturing point of view. The Widney Hinge has received attention for two reasons; firstly because it gives an unbroken hinge line which improves appearance, and secondly because it prevents distortion of the top plate adjacent to the rest buttons which is caused at present by the overhang weight when opened. The weight of the open side of the bonnet fitted with a Widney hinge is taken through the hinge itself and transferred to the opposite top plate, this being a special feature of the design. The top plates are actually mounted on the hinge body the centre line of the hinge pin, and this fact causes the thickness of the top plate material to control the extent which the bonnet may open. In order to obtain what is considered the minimum, acceptable opening angle of 135°, it is necessary to use a top plate having a maximum thickness of the SWG (.064), and due to the top plate being only a little past the vertical position when opened, it would no doubt be found necessary to provide some form of lock to prevent it blowing down in a cross wind. Bonnets have been produced in 16.SWG aluminium and 20 SWG (.036) steel and fitted to experimental Bentley cars for test. The bonnet of 20 SWG steel has proved very flexible, and it was exceedingly difficult to maintain a flat surface during manufacture, furthermore some form of rustproof treatment would be essential on the edges, hence this material may be dismissed as unsuitable for Production use which leaves the 16 SWG. aluminium bonnet as an alternative. This again is considerably more flexible than the present production bonnets and it must be remembered that the bonnets of 30/25 and 40/50 HP. chassis were increased in thickness from 14.SWG (.080) to 12 SWG (.104) in 1930 in order to prevent cracking and buckling. The bonnet side plates used with the Widney Hinge may remain in the present Standard material, hence the problem of cracking from the louvres to the side hinge would not arise but it is doubtful whether it would be possible to maintain the present Standard of surface finish with the 16.SWG. top plates. The bulge which develops adjacent to the bonnet rest rubber on | ||