There is one thing that no one has taken into consideration. It's the eutectic effect. Put simply, some metal alloys have a lower melting temperature than that of the individual constituent metals.
For example, the melting temperature of brass brazing rod is 1650°-1850°F depending on the alloy. Copper, the primary metal in brass melts at 1981°.
Silver melts at 1762°F but some silver brazing alloys have melting temperatures as low as 1200°F. Silver brazing alloys with melting temperatures between 1400°-1650°F were the type most commonly used for bike frames because of the increased strength of these alloys and the ability to fill gaps between the tubes and lugs.
The remelt temperature of most brazing alloys used in bike manufacturing is much higher than the original melting temperature, closer to the point where steel can became damaged from the heat.
At the temperature where the braze becomes liquid the steel becomes very fragile and details in the lugs can stick to the tubing and pull off when the tube is pulled out of the lug.
There are some nickel based brazing alloys that were used in production frame building at one time for making lugless frames (gas pipe balloon tired bikes). They had initial melting temperatures of around 1650°F but the remelt temperature was 2100°F.
Chas. Colerich Oakland, CA USA
> I would think that re-heating the brazed joints should work well
> enough to release the frame tubes.
>
> But, in this instance of the Peugeot lugs...
>
> Who would have a spare Metric diameter tube set?
>
> ... uh... and a Metric bottom bracket shell?
>
>
> Also... I'm not a frame builder, so I wonder how closely the frame
> geometry of a re-built frameset would need to resemble that of the
> original donor bike.
>
> As I recall, there were quite a few different lugs offered in that very
> same lug pattern, in order to achieve different frame angles for a
> built up frameset.
>
> So, another question might be: Would the frame geometry range
> allowed by the particular Nervex lugs which were used for that Peugeot
> racing bike also be acceptable for one's own intended transplant?
>
> I fear it's all a bit more complicated than having a plumber re-solder
> 90 degree elbow joints onto new water pipes to relocate a sink or toilet.
>
> BOB HANSON, ALBUQUERQUE, NEW MEXICO, USA