Here are some basic tips for caring for all tools. Don’t you dare let them rust. Rust spreads like a cancer in ferrous materials (iron and steel) and can make your measuring and cutting tools difficult to use. There are a lot of products out there to prevent and remove rust, but the best thing going cannot be found on the shelf: a small can of vigilance.

When you are done with a tool, wipe down the metal surfaces – especially the cutting surface – with a rag that has been soaked with WD-40. Always keep the rag nearby (mine is seven years old) and renew it with a squirt of WD-40 when it gets dry.  Wiping your tool down does two things; first, it removes dust from the tool. Dust can carry salt. Salt attracts water. The combination of salt and moisture will start breaking down your iron and steel tools.

Second, the WD-40 helps prevent rust by forming a thin protective barrier, albeit one that must be constantly renewed to be effective. Other people will disparage WD-40 (I once did). Ignore them. We tested all the rust preventative products on the market one spring weekend. We applied the products to a cast-iron plate and left the plate outside in the dewy grass for a couple of days. The area treated with

WD-40 came out of the test looking the best. WD-40 is cheap. It’s readily available. It won’t stain your work. Spray some on a piece of wood and watch what happens. Once it dries, there’s nothing to see.

(Taken from Book : I Can Do That! Woodworking Projects)