Old cast iron farm machinery holds a special place in my heart. A pound of grease, a big hammer, and a set of acetylene torches will bring long- neglected implements back from the dead. I have a potato planter which I rescued from a brushlot fifteen years ago, and I have used it fifteen times since then. It had set idle for so long that I had to use a chain saw to cut a small tree that had grown through it.
For most of that day I heated things red hot, beat them with the hammer, and oiled them profusely once they broke loose. Every spring I drag it from the edge of the field for its annual exercise, and it works perfectly with only a few squirts of oil. Cast iron is a miracle material because it does not develop the deep structural corrosion that steel does.
When I go to the airport though, I have to leave the hammers home. Airplanes are made of thin aluminum pieces, and like eggshells, are designed to resist large forces which are spread evenly over their surfaces. Neither eggshells nor airplanes can tolerate stresses concentrated upon one spot, such as a hammer beating upon rusted hardware. Heating rusty screws is out of the question when aluminum melts before steel turns red hot. Airplanes pose special problems when corroded screws must be loosened.
Prevention is the best cure for the problem, hardware is often changed when it first starts to corrode. It removes easily, and the cost is negligible compared to the problems that might come later. Similarly, screws with heads that have been damaged by worn screwdrivers are replaced so that they may be removed more easily next time. Sometimes though, someone else's problem is brought to us.
Patience, good tools, and a few tricks get the job done. When we know that rusty hardware must be removed for a job, we squirt it with penetrating oil the day before. For screws, I use a screwdriver with replaceable bits so that I can always have a "new" bit for a tough job, and I keep a supply of quality bits on hand. Good tools offer the best chance for success.
If the screw head strips out, there is nothing to do but call in the power tools. A handheld die grinder with a 1/16 wide cutting disk can be used to cut a screwdriver slot deep into the screw head for one last chance to turn the screw out. Often this works, because the heat and vibration caused by the grinding can loosen the grip of the rust. The last resort is to drill a hole on the center of the screw so that the head falls loose of the threaded end.
There is one last line of defense to stripped screw heads, a trick that few people seem to know of. There is patience, and there are good tools, but don't forget the valve grinding compound. This silicon carbide grit works just like cinders under a car's tires on a wintry road. A dollop of compound on the tip of the screwdriver will assure maximum grip between the screw and the screwdriver. Using this trick, I have been able to remove screws which were not only rusted, but partially stripped also.
Torches and hammers are much more satisfying to work with, but at least I have a secret weapon for working on old airplanes. Besides, when the potato planter is fixed I have to plant potatoes, but when the airplane is fixed it's time to go flying!