Unfortunately, parts tend to break right at the area of maximum stress, making an epoxy repair that's only a small fraction as strong as the base metal useless in most cases. Could your friend have intended to fabricate a replacement for the broken piece? Indeed, welding small aluminum parts is truly near-impossible, as the moment the affected area reaches liquidus, the whole part very nearly does the same! Silver-solder can be used on aluminum without melting the part however.
David Snyder
Auburn, CA usa
> Help!... A while back I'd picked up a Simplex Super LJ front derailleur.
\r?\n> The band had been broken off right where it encircled and pivoted around
\r?\n> the chrome cable housing guide.
\r?\n>
\r?\n> A local acquaintence, an older gentleman who'd worked his whole life as
\r?\n> a machinist, mechanic and welder had looked over a detailed photo of the
\r?\n> broken component and compared it to a perfectly good derailleur which I
\r?\n> had at hand. He said without hesitation that he could repair it, and
\r?\n> even showed me a small alloy piece (something like a watch bezel) which
\r?\n> he'd recently repaired for someone... and had done so flawlessly.
\r?\n> Unfortunately that fine gent suddenly suffered a heart attack and
\r?\n> recently died before I could deliver the work to him.
\r?\n>
\r?\n> I have no idea how anyone might make such a repair. I assume you cannot
\r?\n> simply "solder" aluminum and must actually weld it - which makes such a
\r?\n> micro-repair seem near impossible. Is there any type of epoxy which
\r?\n> could be used for this sort of repair, or would it actually require the
\r?\n> skill of a master welder (presumably with a super-tiny torch) to
\r?\n> accomplish this type of a fix?
\r?\n>
\r?\n> Appreciate any info or suggestions.