Tony,
FWIW I’m afraid I disagree with those who recommend these “mini chef” gas torches (for use in soft soldering work let me stress) – IMHO the flame is far too hot and far too localised.
And let me also stress that not being a loco builder I have never tried soldering the sort of beading you’re talking about.
But being an old-fashioned aeromodeller I HAVE done a lot of soft soldering with brass, copper, nickel silver, and tin plate, for fuel tanksw, etc, and sometimes using very small sections (e.g. team racer shut-off valves), and sometimes soldering onto “frigging big plates”.
IMHO the very best you can use for this sort of work is a pair of those very old gas-stove irons (IF you have gas at home – unfortunately I don’t). So my 2nd best ideal is a gas blowlamp of the Camping Gaz variety WITH the solder bit to fit (available separately). The iodea is simply to heat the bit and the flame itself is NOT brought into contact with the job (apart from a bit of leakage around the fitment for the soldering bit). That flame is far too hot for brass.
But please also note that even a 100-odd Watt electric iron will NOT do the job if the parent to which you’re trying to solder is a substantial size.
Just as Maurice says above, you need some sort of insulator to stop the heat “leaking away” off the job and I’ve used off cuts of half inch ply, etc in the past.
That plus the use of railway modeller’s low melting point solder and a good flux (I never use resin myself) and CLEANLINESS will make it dead easy after a bit of practice.
So there you are, that’s what works for me – a completely different take to some of the above opinions so as always “ask 10 Model Engineers – I don’t really qualify for that title BTW – and you’ll get 12 differnent answers”.
Good luck with it and hope the above helps. – as said, just what works for me
Krgds
AES
P.S. I find that either “Typex” (that white “paint” for correcting typing errors) or child’s crayon rubbed onto the area where you do NOT want the solder saves a lot of cleaning up grief afterwards – another reason for keeping the temperature “down” to solder melting levels by using an iron , otherwise a direct flame would, I guess, burn the Typex or crayon off.