On Sat, 31 Mar 2012 20:40:02 -0500, 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?

I'll limit my comments because I haven't used that solder, nor am I
sure what the flux is. But I have a tip that may help get a better
bond on the music wire.

Tin it with solder before putting it in the ferrule. I've soldered a
lot of steel and I never use anything but a commercial acid flux for
steel, or, when I was in school shop classes, shop-mixed zinc
chloride.

You have to clean those fluxes off after soldering but that shouldn't
be a problem on the wire. Then you'll have a nicely tinned surface to
solder to your aluminum. It should produce a much stronger joint.

--
Ed Huntress