There's nothing worse than that sinking feeling
you get when you're taking the horn apart and and a screw doesn't
move. This is the worst situation a repair technician must face.
The potential for disaster is high. You can very easily make this
bad situation much worse in your attempts to remedy it. The
procedures outlined below should only be attempted if you are
comfortable with them. You can seriously damage the instrument if
you do it wrong! You have been warned!
First, we need to determine why the screw is
stuck. Either the key is bent, or the screw itself has become
corroded. There is always the possibility that both situations
exist simultaneously! Take a good, close look at the key. Is it
bent? If so, you're going to have to straighten it as best you can
while it is still on the horn. Use round nosed pliers to bring it
as close as possible back to its original shape. Take great care
to avoid scarring the metal! It will most likely prove impossible
to completely straighten the key with it on the horn, but if
you've been living right, you'll be able to get it straight enough
to get the screw out. After the key is straight, apply the best
penetrating oil you can find (I use Corrosion Cracker from Ferree
Tool) liberally to the key, heat it to facilitate spreading of the
oil, and wait overnight. It takes the oil a while to work its
magic, and the process can't be hurried. If you're lucky, the
screw will turn the next day and you're out of trouble.
Unfortunately, this is not always the case.
When trying to turn a frozen screw, be sure to
always use the biggest, longest, meanest screwdriver you can find.
There is no substitute for the leverage of a big screwdriver.
You'll never get a stuck screw out with a small one! Pay close
attention to the condition of the tip of your screwdriver: the tip
should be even and sharp enough to bite into the metal of the
screw. If the tip needs some attention, sharpen it with a file.
Always be sure that the slot in the screw head
is clean enough for the screwdriver to get a good grip. If the
slot is damaged, and if the screw head protrudes from the post,
you can cut a new slot with a jewelers saw. Do not, under any
circumstances, allow the jewelers saw to cut into the post!
It is often helpful to have an assistant wiggle
the key as you try to turn the screw. Move the key in both
directions, as this will help break loose any corrosion that may
have developed over time. The assistant is also quite useful in
providing moral support, acting as a cheerleader, and giving
assurance that everything is ultimately going to work out well and
that the fact that the screw has refused to come out does not mean
that the technician is not a good human being.
If the screw has still refused to move (and it
often does); I next consider the removal of the post nearest the
slotted head. This, of course, is not an option if the post is
attached to a long rib. If the post stands alone, un-solder it
(take great care not to burn the lacquer) and expose a little more
of the screw. After considerable prayer and encouragement from
your assistant, grip the exposed end of the screw with Vise Grip
pliers, and as the assistant wiggles the key, try to turn the
screw. The Vise Grip pliers will often scar the rod, but these
marks can be polished out with emery paper.
At this point, I'm going to assume you have
successfully removed the stuck screw. Let's talk about what to do
with it. If the screw is bent, then it is also probable that the
hinge tube of the key is bent as well. I usually trust my eyes and
straighten bent tubes with my fingers. It is virtually impossible
to get them perfectly straight. It is important to keep in mind
while you are manipulating the bent tube with your fingers that
you want to take great care not to make matters worse. Insert a
straight screw or metal rod of slightly smaller diameter than the
hinge tube to prevent kinking. Then, insert a screw of the same
diameter and see where the key binds. Take a hinge tube file and
carefully file away the high spots until the key spins on the rod
perfectly. Now let's return to the original bent screw that we
have successfully extracted.
I use a granite block which is level to .0015
to check screws for straightness. Really short ones can be checked
on a jewelers anvil. Roll the screw across the block and see where
the bends are. Use a rawhide mallet to give the screw a few good
whacks at the points where it is bent. You'll be amazed at how
straight you can get it using this method. Following this, I
insert the screw in the jaws of my bench motor, and work the
remaining small kinks out with a hammer which has a small hole
drilled in the handle which is slightly larger than the screw.
This procedure is very dangerous! Do not allow more than four
inches of the screw to protrude from the jaws, and only deal with
one kinked area at a time. Be certain that the screw is centered
in the chuck jaws, and be aware that the screw can whip around and
cause serious injury.
Check the screw and key for straightness with
each other by spinning the key on the screw. If it doesn't move
perfectly, repeat the steps outlined above. Reassemble the horn,
and consider yourself lucky that you were able to solve the
problem.
If the process described above does not remove
or straighten a bent screw, then more radical procedures are
called for: sawing the screw out by cutting the key; extracting
the screw with an "easy out"; or drilling the screw out.
All of these procedures will require the fabrication of another
screw and are not something you should attempt yourself. That's a
topic for another day!
