I was visiting a friend of mine, Rob Hubbard, at Kitt Peak several years ago. He was giving my wife and me a tour of the observatories shortly after one of the observatory technicians had been killed by the dome. (It was rotating, he stepped from the main floor into a door to the catwalk, but only half of him made it through.) Rob was telling us that the OSHA safety people had been out afterwards and had ordered many, many safety changes to the building. Halfway through ordering a number of upgrades, which included much increased lighting, the inspector suddenly realized, “Hey! You guys are Astronomers! You have to work in the dark!” Rob was shaking his head that some guys get so wrapped up in doing their jobs that they no longer can see the obvious around them.
Being astronomers, we usually work at night. And usually outside. That means that our equipment gets exposed to thermal cycles and lots of water condensation (dew). Little drops of sulfur dioxide saturated water which bridge two different kinds of metals make a battery, and the electron motion then creates an oxidation reaction. It you’ve ever worked on an old car, you’ve probably noticed that the fasteners can sometimes be pretty hard to remove because of this phenomenon. Telescope mounts that are rode hard and put away wet can have this problem, too.
The solution is simple. Just prevent the electrons from flowing. This can be done by making our telescope mounts out of materials that have similar electro-negativities (which reduces the voltage difference between the metals), or by placing an electron barrier between the metals. Compatible materials include aluminum and stainless steel, and regular steel and brass. (But not aluminum and brass, etc.) The designers of the McMath 24” went with steel and brass, but most of us will probably use aluminum and stainless. Tables of various metal’s electron potential can be found in most engineering books.
Putting an electron barrier between metals is a second choice. I’ve heard that the builders of Rolls-Royce automobiles place a special waxed paper between the bolted-on body panels. We can use a simpler solution in the form of Loctite. Not only does it keep water out of the contact area, not only does it provide a vibration-proof and controlled release forever and always, but it’s use also shows that you have thought about how your creation is going to be used, and that you care.