On Sat, 15 Mar 2008 15:17:44 -0700, Bruce L. Bergman
wrote:

On Fri, 14 Mar 2008 19:51:09 -0400, "Sam Soltan"
samsoltan_48323atyahoodotcom wrote:

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
break off.

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.

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'.

-- Bruce --

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.
(Think billet)

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.

--
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