Ouch, Mike.. that last reply about the Rudge fork crown stung! But you were correct in your correction...However that was a "trade mark" item in the same way as the Raleigh tubular one.. although Fiorelli plagiarised that one. I think this thread is talking about crowns available to frame-builders.. or ones that builders fabricated for themselves.
The still have four pair of rapid taper chainstays in stock and they are all stamped "Reynolds 531" Many of the Rotrax, Hetchins and other UK lightweights from the 50/60s used this form of stay.. and presumably would be 531 throughout. I am assuming that the same stays in my 70s Carlton Flyer will be 531 too. I have so few Accles and Pollock frames, but none of them has rapid taper stays. Raleigh Industries used "Truwel" stays in certain frames. These were seamed tubes, but not of 531 steel.
Concerning the effect of the shape and gauge of seat-stays, I would suggest that the pencil stays did give a more comfortable ride, and I cannot recall any problems with vibration under braking, flexing etc. In the 50s we often used to use the same bike for most purposes eg club runs, time-trials,,and Youth Hostelling holidays, continental tours.. and sometimes even cyclo-cross. I have done all these on Rotrax, Hilton Wrigley and similar frames without any problems of handling.. or of discomfort. In the late 70s/early 80s when Colnago, Pinarello , Ciocc etc frames were becoming popular in the UK, UK builders had to try to emulate them. I produced a lot of road racing frames at that time and was often told by top amateurs that the success of the Italian frames lay in the handling, cornering abilities. These riders swore by the Columbus SL seat stays which came as biconical plain gauge items. These, it was claimed, gave a far better "compliance" whereas the single taper Reynolds tended to "skip".
Pencil seat-stays were fairly standard in the 50s on large frames as well as small ones. Rensch took the idea to extremes on his Paris and own-name frames.
Returning to the Herse theme.. ie building a copy.. I wonder if he used rapid-taper chainstays? Or Singer for that matter? Someone on the List should surely know that answer. The Herses that I have seen used either a Wganer-type crown, possibly "altered" by Rene, or one of the twin-plate flattish ones, seen on Peugeot and Gitane tandems... and many others too.I know that the French builder Didier Louis also made his own sloping crowns in the 70s, but of a quite different and ingenious .. and slightly worrying.. design.
If I was to attempt to... and it's a tempting idea.... to build a Herse copy, I would adopt the twin-plate flattish crown, use a bilaminated type of construction and possibly use old section Reynolds fork blades as chainstays. Another question for "Herse cognoscenti" - did he use an oversize top tube on his lugless frames.. ie the same diameter as the seat and down tubes?
Returning to the notion of stiffness in rear triangles... as a builder I certainly notice a difference between certain types of stays.. and their resistance to movement, when I am tracking or realigning a frame.
Just one last point. In 50 years of building my own frames, repairing and selling other peoples, I have never known a frame collapse in the rear triangle due to it having pencil or any other type seat stays. I have known chainstays break, for a variety of reasons. Probably the worst thing that I have seen happening with seatstays related to the biconical ones produced by Reynolds for their 531 SL, or possibly 531 Pro series. A friend who is a frame-builder built a set of cyclo-cross frames for a leading amateur team. To get some degree of lightness he used this type of stay, little knowing that, at the "fattest" point, just near where he had brazed on the cantilever pivots, the tube was at its thinnest. To cut a long story short, the effect of constant braking and the torsion resuling from it, was to produce cracks at the point of the brazed-on pivots. He was told, later, that the biconical shaping was produced by "blowing out" the stay under oil pressure thereby producing a tube that was thinner in th middle bur thicker at the ends.
Norris Lockley... sifting through a box of 50s frame "bits".. Settle UK