As a veteran of decades in the elevator craft, cleaning contacts is best approached as "It depends". Relay contacts designed for millivolt level signals often have gold plating. It is frightengly thin, and clean paper with a little solvent will get the schmutz off without destroying the plating. Contacts carrying signals and current at intermediate levels, up to about ten amps, can be cleaned with a burnishing tool, preferably diamond. Take it easy, don't take off too much metal and flush the cleaned surfaces with solvent if you can. For heavy currents, ten amps and up, the contacts are usually a silver/cadmium alloy. Use a diamond or steel burnisher. Unless they are really big, don'try to file out the craters. just level the spikes, removing as little metal as you can while getting the job done. It's normally wise to flush the contacts witha spritz of solvent. Don't use sandpaper or emory cloth, they embed abrasive crystals in the contact surfaces and can be worse than doing nothing at all.
Bruce Gentry, KA2IVY
Andy,
Filing contacts is likely to take off a thin coating contact of contact material.
I use strips of card stock pulled between contacts as I hold them together. They will will come out with a black stripe.I usually dampen the strips with alcohol at first. Then I pull dry strips through until they come out clean. I willgo through many strips. Paper is cheaper than new contacts!
If you have been filing contacts you may already have ruined them and they will need to be replaced.
Tom N3CRK
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