This is one of those projects that was certainly not worth doing in a cost/
value perspective, but every once in a while I'll get a project that I just
want to do. This wasn't really one
, but I took it in assuming a simpler
repair, then of course quickly became more complicated. This was cool
enough though that I was willing to put a bit extra than what I could
charge for, simply because I liked it and was up for a fun challenge.
'59, Kay Barney Kessel Jazz Special, blonde with Kelvinator headstock.
Pretty much the coolest guitar Kay ever made. Neck joint loose, not
unusual, and truss rod broken, which is pretty common too. The truss rod
system on these things never worked, and are often broken trying to
make them work. They used a stamped U-beam, curved at the headstock
end to create an pivot point at the end. The slot is cut deeper as it
approaches the heel, and the beam rests on the bottom of the slot when
it is relaxed, leaving a gap above it.
At the heel end there is rod anchored to a plate right under the
fingerboard, passing through the end of the beam, then through a long
aluminum spacer, threaded at the end with a nut accessible from the back
of the heel. Tightening the nut will force the spacer against the beam,
pushing it upward in the slot. Then there is another plate a bit less than
half way along the neck that holds the center of the beam down in the
slot, intended to act as a pivot point so that as the rod is forced up at the
heel it would push back down at the headstock end. I wish I was good
enough with some drawing programs to sketch it out for you, but
hopefully you can visualize it. It was a stupid design to begin with, and I
don't quite know how they ever thought it would work.
The person who broke this truss rod apparently didn't want to tell the
owner, so they kindly glued the truss rod nut back on. Certainly not the
first time I've seen that, but they used a half bottle of thin superglue
which successfully filled about a third of the truss rod slot. Normally I
would have just replaced the truss rod with a standard one adjustable
from the headstock, or through an access hole in the fingerboard
extension. This one however, I really wanted to keep original (as viewed
from the outside anyway) with the adjustment through the heel.
I decided on a double action truss rod, and tried a few crude right angle
mitre gear ideas to access it , but ran in to problems with the amount of
force those double action rods take to turn. With the double threads they
are effectively the same as turning a 16 thread per inch nut, rather than
the usual 32 tpi. So here's the contraption I came up with.
I picked through some old tuners to find a suitable worm gear / sprocket
set. The original tuner plate and journals just weren't stiff enough to trust
in a forever inaccessible area, so I machined a brass box with a bit tighter
tolerances. Then I had to add another box below with gears to offset it
back to center, in order to line up with the heel access hole. The set had
to be made at an angle, both to fit within the heel as well as to line things
up properly. The hole ended up getting a bit larger than I needed in the
end, due to fitting for some failed early designs. A few quick filler shims
though and everything worked out.
It's all completed now and works great, though I'm still dealing with a
fussy touchup. Not something I plan on doing again, though if it comes
around I'll know how to quote for it next time. My substitute camera I'm
using sucks, and the pictures are a bit blurry, but oh well. This project
was unique enough that I felt like sharing some details.
Nice work. Great design.