What kind of oil or lubricant should I use for metal parts?

I'm building a small machine as a hobby project and have a problem -- the metal parts are rusting. I have quite a few ball bearings that are supposed to roll along aluminum trim channel, and I recently found that the bearings (which had been sitting in the basement for a week or two) had rusted really badly. Is there a type of lubricant or oil that I should put on them to protect them from rust?





I also have a threaded rod constantly turning a nut, what kind of lubricant should I put on the rod to keep it turning smoothly?





That's really two questions, but they're related.. Thanks for your help!What kind of oil or lubricant should I use for metal parts?
To stop the ball bearings rusting, probably all you need to do is keep them dry. Keep them in a container (so they are not in a steady flow ot air carrying more moisture) with a packet of silica gel to take the moisture out of the air in the container. If you have something like a ball bearing standing on a flat piece of metal, water tends to get drawn into the small gap between the objects by surface tension and then corrosion starts.





For your threaded rod, the biggest problem will be actually keeping the lubricant where it does something useful. Putting some grease on the nut will probably work better than trying to keep the entire rod covered in an oil film (which would collect dust and dirt and may end up making things worse not better).





If the loads on the parts are small, you could try a brass rod rather than steel (brass is softer and more ';self-lubricating'; that steel) or use nylon nut instead of a metal one.





WD40 was originally designed as a water repellent rather than a lubricant, but if the loads on the parts are small enough so that a film of WD40 can form a ';dry'; coating on the parts and not get rubbed off when the machine operates, it will work very well.What kind of oil or lubricant should I use for metal parts?
W D 40 or similar, any good hardware store will help you and it's not expensive .
WD 40 is not really a lubricant. Motor oil or axle grease will provide lubrication and provide protection against corrosion so long as a continuous film covers the steel parts. One thing to remember is that grease will increase the amount of torque required to move parts )although not as much as pieces of rust). So as long as your drive produces enough torque, you should be ok. Graphite is a better lube in some situations as it does not increase the force require to move the parts but it will not provide corrosion protection. good luck