I have a Hohner GT3 headless guitar ( a knockoff of a Steinberger) that has
develops a slight bend as has a crack starting at the bend. I believe the
alloy is aluminum that is cast and then machined.
I fear that if I try to bend the part straight that the metal will crack and
I wonder if I could use the rod I saw advertised on TV that "welds" (seems
like soldering to me) using a gas torch.
Has anyone experience with this stuff? Please comment pro or con.
This stuff has been around for decades, every so often somebody dusts
it off and brings at back as the new "miracle" soldering rod. It's an
alloy of tin and zinc, has to be rubbed into the mating aluminum
surfaces to displace the oxide and really isn't very strong stuff. It
also doesn't wick into cracks. Not welding at all, no aluminum in it,
it's a solder. Probably wouldn't do what you want.
This IS a metalworking group, why not get a billet of alloy and start
I've used it quite a bit. It works, sort of, but I'm pretty sure it
won't do your job.
The process is more like welding than soldering, except that the stuff
itself is technically a solder.
Welding refers to the process of joining (usually metal) by locally
melting the joint - and usually adding a filler of the same material.
Soldering is the process of joining with a material of a lower melting
point than the items to be joined; the items themselves do not melt.
When soldering, the molten solder wets the joint and flows into it by
capillary attraction, and when it freezes the joint is made. For
soldering to be successful the molten solder must wet the joint, and
this is where the problems start, it won't wet a dirty joint. And for
most metals the very act of heating the joint makes it dirty - the
oxygen in the air reacts with the hot metal to create oxide which
prevents the solder from wetting and flowing. There are only two ways
around this: solder in an oxygen free environment, or use a barrier to
prevent the oxygen from reaching the joint. The latter is the most
convenient method, and the barrier is called a "flux".
Aluminium is particularly difficult to solder because the oxide forms
almost immediately at room temperature and there are very few fluxes
that can get rid of it.
The "welding" rods you mention are not made of aluminium, so they don't
actually weld, they also have a lower melting point than aluminium. They
are used to "tin" the components of the join before bringing them
together. You first clean the joint area with a stainless steel brush
then heat it until the tip of a rod melts when it touches it. You then
spread the molten rod material over the joint area with a thin stainless
steel rod, making sure to scratch the joint - this removes some oxide
and the molten solder itself prevents further oxidisation. Keep
scratching through the molten solder until you're happy you've removed
all the oxide, then remove the heat and allow the solder to freeze. You
do this for all the components of the joint.
You then bring the components together and reheat the joint until the
solder melts again, remove the heat and the joint is made. A flux is not
used because the solder itself doesn't readily oxidise.
You can now appreciate that this method will not allow the solder to
flow into a crack. The solder itself is quite strong - stronger than
most aluminium alloys, so you could use it to fill a crack that has been
"prepped" into a V-groove. But there is an additional problem: a lot
of aluminium alloys are heat treated and the act of heating to melt the
solder is likely to anneal (soften) it so much as to make it no use for
its intended purpose.
I hope this has helped with your decision.
You oughta see the guys at the MN state fair work with this rod! They
do GREAT things. But take it home and try it yourself????? Maybe, if
you are already an accomplished welder who also understands brazing very
There are at least 2 kinds, the last I knew. One kind REQUIRES the
stainless steel brush (which comes with the packet of rod). The other
kind supposedly does not. Sorry but I don't rememeber why not.
A funny story for y'all on the subject:
I did buy this rod many years ago. The package of about 20 1/8"
diameter rods about 18" long, with SS brush, cost me $30. I kept it
around for years looking for an application.
My old Cub Cadet developed a head gasket leak right beside the
exhaust valve and by the time I noticed it, the hot gases had burrowed a
groove in the aluminum head.
Got a new gasket and found that the new head was gonna be $60, so
decided to give the rod a try, Vee'd out the crack, brushed it well
and did the soldering. Looked great. "Milled" it flat on a surface
plate/ sandpaper and reinstalled it. Worked like a champ!!!
Went back to mowing. Once the head got up to temp, the whole slug
of whatever it is came flying right out of there in a molten state.
Bought the new head.
Sam Soltan wrote:
Not going to work in that application - it's like soft-soldering it
with tin. Won't handle the same stresses that the parent metal does -
or in your case didn't.
Plan A: Call Hohner and see if you can order a replacement neck.
You probably aren't the first one that has this problem, and they
often revise the design when these sorts of flaws appear. And even if
it sounds expensive, it's probably less than a proper repair.
If that fails and it's still worth the effort to save that guitar,
you need to totally disassemble the neck from the body and find a true
"artiste" with a TIG welder. Because the spread between 'welding
temperature' and 'big puddle of molten aluminum all over the bench
temperature is VERY slim - meaning a high screw-up potential.
You need someone who TIG welds on delicate things like $50,000
injection molds (or similar) all day. I know only one someone like
that, if he hasn't died or retired & gotten totally out of practice...
Sometimes you can put a clay "Tinker's Dam" around the item so if it
does melt more than expected it is contained and can still be saved
cosmetically - but it'll never really play the same. Especially the
fretboard, too much precision is required - if it shrinks or stretches
any in the fixture you'd have to re-machine the whole neck and re-cut
all the fret slots, or the relative tuning goes away.
My best guess at a fix procedure would be to cut open and clean out
the cracks with a hacksaw, and stop-drill across at the root of the
crack so it can't propagate any more. Then make sure it's bent
straight and true, and devise a metallic clamping fixture to hold both
ends of the neck rock-solid in the right position. (And make sure the
fixture can take some serious heat, as it's all going into an oven.)
Then scrub out the crack with flux and a stainless wire brush.
The welder will have to pre-heat the whole casting & fixture in an
oven, then clean out and flux the crack area again, and fill in the
entire crack in several passes with TIG weld filler metal. After
that, you have to clean up the outer welded surfaces with files,
grinders and sanders, and buff it out smooth. And repeat any heat
treat and/or anodizing steps to restore the strength and appearance.
The weld filler is a slightly different composition and is not going
to take anodize or finish the same as the base metal, but you should
be able to make it 'not obvious'.
First you need to know the alloy used. Many aluminum alloys are NOT
weldable even under the best of conditions. Some also can not be heat
treated and will never have adequate strength after welding as they
need to be work hardened. Many forged parts would be in this category.
It's also surprising just how strong one of those torch filler joints
CAN be. The stuff is harder than the base metal in many cases but you
would need to "V" it out to get any strength and I don't think this is
really a good aplication for it.
Price the replacement part first, then decide how much/little you want
to spend trying to save the old part, and what your risk tolerance is.
If not too expensive, but more than you REALLY want to spend, you
might want to risk trying a DIY repair first, and if it does not work,
order the new paert.
On Sun, 16 Mar 2008 12:50:38 GMT, with neither quill nor qualm, "Carl
Byrns" quickly quoth:
What, you've never heard of Weldwood products?
Shake off all the fears of servile prejudices, under which weak minds
are servilely crouched. Fix reason firmly in her seat, and call on
her tribunal for every fact, every opinion. Question with boldness even
the existence of a God; because, if there be one, he must more approve
of the homage of reason than that of blindfolded fear.
-- Thomas Jefferson
Unfortunately, I do not maintain the FAQ, only post a periodic pointer
to it. To add something like this to the FAQ, contact Jim
Kirkpatrick. I honestly don't know if he is still handling any of it
though. His address is provided near the top of the FAQ at:
The last contact I have had with him was a little over 4 years ago.