David Benson brings up an important point to consider - in the thirties it was a standard process to flame weld the various types of tubing that were used in aircraft construction. A filler rod was employed and the results could be very nice indeed - depending on the skill of the welder, of course. I discovered this in an old book on aircraft welding from @ the late 1930's, or maybe it was the WW2 era. If I recall correctly, the gas of choice was a Hydrogen/Oxygen mix at low pressures. Like many welding processes it was not easy to master, and the problems with getting a reliable joint to survive aviation service is what I believe led to development of the TIG process during WW2.
Enough with welding history - but it makes me wonder if some of those early lightweight frames Mick and Norman refer to might have been STEEL fillet welded with a torch ? They would probably have been Reynolds HM (531's predecessor) or Accles and Pollock (aka Accles and Bollocks)Kromo - both of which would have worked with the process. I imagine that these frames were produced as a means to save money on time and materials compared to a lugged frame, and steel filler rod has always been cheaper than brass or bronze.
It would be interesting to see if anyone remembers repairing or repainting any of the welded/bronze welded frames in question, and if they recall what was used to stick them together.
Mike Fabian in San Francisco who wonders what exactly holds those modern plastic things together ?