You really should silver solder such mounts because it requires much
less heat than brazing does, and is therefore less likely to weaken the
tubing. The area where you're going to be adding the bottle mounts is
the thinnest part of the butted tubing, and is especially prone to
weakening when brazed, although the mounts themselves do tend to
reinforce the tubing at that spot. The problem is, if you use too much
heat (as in brazing), the weakened, overly-tempered area extends well
past the bottle mount itself. If you don't have an oxy-acetylene
torch, you can silver solder with a propane or MAPP gas torch that you
buy at the hardware store. It really requires very little heat, and
minimizes damage to the frame's paint. First, I'm kinda assuming you
know how to lead solder small stuff with a soldering iron and get good
solder flow with the minimum heat. If you don't know how to do this,
first practice soldering wire to electrical connecting lugs with rosin
core solder and a small soldering iron. You've got to keep everything,
including the soldering iron tip, scrupulously clean to get good flow.
Then, when you begin silver soldering with the torch, practice on some
thin-wall junk tubing, and use a VERY SMALL tip and a VERY SMALL flame
(the smallest tip, and about the smallest flame you can get). Drill a
hole in the junk tubing and put a small (standard galvanized) machine
screw in the hole. Then silver solder the head of the screw to the
tubing. This will simulate what you will be doing when you silver
solder the bottle mount to the frame. Practice doing this until you
can get nice flow all around the head of the screw just after point
where the solder melts, and then withdraw the heat. Mount the tubing
level when you solder so you will be harnessing gravity to get the
solder to flow where you want it to go. Be sure to clean the tubing up
until it is shiny and apply some silver solder paste flux before you go
to it. When you solder the mounts to the bike, be sure to drill
through the tubing where the mount is going to go, and clean the
threads of the mount out with a tap after you solder it; otherwise, the
screw holding the bottle mount will likely bottom out before it engages
enough threads and strip out the mount. The only problem is, once your
friends find out that you're proficient at silver soldering things like
this, they will be continually asking you to put mounts on their frame.
