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 and material considerations for rivetless car bonnets, comparing steel and aluminum options.
| Identifier | WestWitteringFiles\V\March1931-September1931\ Scan266 | |
| Date | 18th June 1931 | |
| TO HS.{Lord Ernest Hives - Chair} FROM EV.{Ivan Evernden - coachwork} COPY TO [REDACTED] ORIGINAL RE RIVETLESS BONNETS. EV{Ivan Evernden - coachwork}2/18.6.31. J385. x7260. x5260. This is to confirm our conversation re the matter of rivetless bonnets by telephone yesterday. You say that countersunk rivets in aluminium cannot be considered, and our experience endorses that conclusion. In connection with the steel bonnet we suggest that as you have no electric spot welding plant, the best way to get a steel bonnet welded up would be to send the pieces to some firm that does such work extensively, such as the Pressed Steel Company of Gt. Britain. at Cowley. STEEL BONNETS. It was agreed that you would proceed to build up a bonnet preferably for the 20/25 HP. having panels of 22.SWG. steel. The hinges to be of the same design as now but in some untarnishable steel, and the side hinge to be sheathed as now, in all cases in the place of rivets we suggest electric spot welding. The stiffeners are to be in steel as on N.2. Series P2. You have a design for a flip-flap shutter in steel. We now make a few observations on steel bonnets. Rust will be their biggest drawback, both blistering of paint, but worst still, red rust stains will be washed over the paintwork from the ends of the bonnet where chafing has occurred. So far we have been unable to make any use of the idea of making the hinges in the edge of the panels themselves. The hinges cannot be painted as opening and closing the bonnet cuts the paint off the sectors. We see that it might be possible to sheath the side hinge with a strip of brass or steel sweated on and subsequently chromium plated, but we cannot see a way of covering the top hinge on account of the way in which it opens. Also we fear that as the hinge material of the hinge would not be rustless terrible staining would occur in the case of light coloured cars. ALUMINIUM BONNETS. Our original suggestion of using countersunk rivets in all places except the hinge joints having proved useless we have to give the matter a fresh consideration. We shall send to you by the weekend a design for a bonnet in aluminium preferably for P.2. having concealed hinges at the sides, the hinges in all cases being attached by snap headed rivets which are not visible. The only way to deal with the stiffeners is to do away with them, and hope to make the bonnet stiff enough by thickening it up to .104ins. Likewise there will be no wearing strips, but to help in preventing the bonnet being eaten away we are suggesting a rubber bearing material instead of ferodo. The only rivets left will be those attaching the flip-flap shutters, and then only four per shutter. We are inclined to think that we shall prefer this bonnet to the steel one for P.2. and perhaps for the smaller car. EV.{Ivan Evernden - coachwork} | ||