[TowerTalk] Brazing copperclad rods to #2

[Peter Chadwick]

The advantage of silver soldering is that it happens at around red heat, and you're less likely to get burning of the copper or steel. The last issue of NCJ had a good article on silver soldering, although there were a few points not covered. The flux used can be something as simple as household borax made into a thick paste with water, although I use a commercial flux called 'Easyflow', which you mix with water to a thick paste. Silver solder, depending on which one you get, flows at between 600C and 700C.. the NCJ article said you mustn't have a gap: in fact, you need a gap between the materials being joined of between 2 and 8 thousandths of an inch, depending which silver solder you are using. The UK 'Easyflo #1' melts atbout 610C and needs a gap of about 1 to 2 thousandths of an inch.
As others have said, for silver soldering, make sure everything is as clean as for soft soldering - no grease from fingers! - and use lots of flux. You usually find that the excess flux  comes off easily by pouring some cold water over the joint - for small copper locomotive boilers, it's not unusual to pickle in dilute sulphuric acid, but that's a bit OTT for this application!
Incidentally, mixing the flux is like mixing epoxy - you can only get two quantities - too much or too little! Too much is preferred....

73
Peter G3RZP