The early Thanet Silverlights had a high failure rate - they were built lugless and the problem was not generally the joints coming apart but the tubes tearing close to the fillet. Within about a year most joints were given either lugs or some reinforcements and most of the problems with broken frames disappeared. The top tube/seat tube area remained practically lugless for all Silverlights - there was just a shaped reinforcement on the back of the seat tube around the slit. However Silverlights were always less reliable than a conventional frame. This was not due to either the silver brazing - incidentally they used an Easyflo rod mostly - or poor workmanship but the design. The bottom bracket design whilst looking interesting was definitely not a help a contemporary engineer wrote: If any constructional draughtsman showed such a construction on his drawing board, his dismissal would follow soon afterwards. A main principle is to keep away from secondary stresses. Thus the centre lines of converging components must meet at one point. This is the case with a normal crank bracket. With the Thanet every tube is off set from the bracket and so there is severe bending stress where the tubes are tangent to the bracket. ¹ Additionally the chainstays are considerably more slender than conventional ones. All three main tubes were 1in in diameter and both the down tube and seat tube in the thin gauges used were overstressed as a result. The gauges used were very similar to standard 531 db tubing - 0.5/0.8. In the early days 531 was used exclusivlely but from 1951 on Accles and Pollocks Kromo tubing was also used. I have never seen a spec for Kromo but am sure it was a fairly typical chrome-moly steel alloy. At the time Thanets found that Kromo made for a more reliable frame; however in hindsight using the frame build records that exist and the surviving frames that 531 frames have proved to be nearly 50% more reliable in the long term. However the building of Thanet Silverlights did not stop due to frame reliability problems but due to a big downturn in the cycle market. Petrol rationing (after WWII!) at long last finished in late 1953 and all lightweight framebuilders experienced a very sudden decline in orders. Bates closed most of their shops almost immediately and a year later were left with one shop, Hetchins rapidly cut frame production which then declined every year until the middle 60s. Thanet were in a similar position. It was not helped however by the fact that Eddie Oliver, Thanet's framebuilder at the time left to become a milkman - he could make more money that way! Frame production was transferred to Rotrax at Southampton but only a few Silverlight frames were made there - probably less than 30 - unfortunately the records from this period have been lost.
Hilary Stone, in the home of Thanets, Bristol
Mark Bulgier wrote:>
> We've been discussing silver fillet brazing on the framebuilders' mailing
> list lately, and one fellow just posted that "Thanet Silverlights were
> pulled from the market due to a high rate of failure, and the brazer's in
> that workshop were excellent." -His point being that silver fillet brazing
> is too dangerous, if even excellent brazers couldn't make 'em safe.
>
> Is this true? Any Thanet experts want to comment?