On Sun, 01 Apr 2012 15:49:26 -0400, Joseph Gwinn wrote:

In article ,
Tim Wescott wrote:

This is kind of a product review, kind of a "how to", and kind of a
"how not to".

But mostly, it's a request for the RCM brain trust to review what I've
done and figured out, and to straighten me up if I'm going in the wrong
direction.

Quite a while ago I got a Harris "Al-Solder 500" kit from the local
welding shop. This has some 85-15 tin/zinc solder, some Harris "Stay-
Clean" flux, and a rather alarmingly long MSDS (short story: don't
breath the white smoke).

I got this for the purposes of soldering aluminum ferrules onto steel
music wire, the purpose of the ferrule being to provide a good bonding
surface to a carbon-fiber arrow shaft. With that, I can make pushrods
for control line airplanes that are more rigid and lighter than ones
made all of music wire.

So, partially from inertia, and partially because of the warnings on
the MSDS, I've been making the ferrules from brass because I can solder
them with plumbers solder relatively free from worry.

Today, I went and made some ferrules out of aluminum, and gave the
soldering a whirl.

The first one I tried was completely unsuccessful. The directions
implied that the soldering could be done with a torch at the same time
they mentioned that the flux became inactive at barely above solder
melting temperature. I tried it, with a torch, and things failed
miserably. So miserably, in fact, that I've got a couple of pushrod
ends sitting on my bench right now with brass ferrules.

After I got the replacement ferrules soldered, and as I was cleaning up
the mess, I decided that since the soldering iron was hot anyway, and
since the solder is supposed to work at 450F, I'd try it on the stuff.
So I slapped some flux on the ferrule, put the iron to it, and melted
on some solder. It worked! Rather like magic -- I didn't have to
scrape on anything or do anything special other than not snort the
smoke (and it is evil-looking: there's something about dense,
pure-white smoke that puts me off).

Then once I had a ferrule with solder on it, I took some music wire,
sanded it, and stuck it into the hole with the iron on it. This didn't
make a good bond -- a light whack with a center punch and a piece of
fir 1x2 and the music wire came right out. Crud.

But I saw that the bond to the music wire was pretty crappy, so I
slathered flux on the wire, put things together, and tried again. This
time I (probably unnecessarily) made sure to pull the wire out of the
ferrule a bit, to make sure I had solder on it, then pushed it back in.

This second time was much stronger: I did manage to whack the wire out
of the ferrule, but I had to give it a pretty good thump: I'm sure that
the impact I gave it was way more than I'd see in normal use, and if it
happened in a crash there'd be a lot more damage than one cruddy little
solder joint.

So (goodness this is taking me a long time to say), it looks like the
proper technique with this stuff is to treat it like regular solder and
flux, with the possible exception of being very careful about the
fumes, and (also possibly) with the exception that I shouldn't expect
the solder to wick into joints with the enthusiasm that tin/lead solder
does.

Does that sound about right?

My experience with soldering music wire is that you *must* abrade the
oxide layer off the surface before soldering with zinc chloride acid
flux (tinners' flux), that flux alone won't work. I use wet-dry
sandpaper wet to do the abrading.

I would follow Ed, and pre-tin the music wire before soldering the wire
to the aluminum ferrule.

Yea, I left out the part about sanding the music wire -- because one
always needs to, as you mention...

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com