WD40 IS a lubricant, but not a good one. It is also a solvent, and an excellent cutting fluid. It does NOT gum up in normal use-this is a myth. I have used it for 35+ years, for many things. I have seen no evidence of gumming yet.
3 in one oil is fine for knives.
Bill
IIRC WD-40 was originally designed as a Rust preventive/degreaser for the Aerospace industry. The WD stands for water displacement and the 40 stands for how many tries it took the to get the formula to what we are now using. I agree with Bill D. , it leaves no gummy residue and is fine for knives, as is 3-in-1 oil......which incidentally is made by the same people.
I personally have used it about as long as bill has, for just about everything.
Quoted from WD-40.com:
"In 1953, a fledgling company called Rocket Chemical Company and its staff of three set out to create a line of rust-prevention solvents and degreasers for use in the aerospace industry, in a small lab in San Diego, California.
It took them 40 attempts to get the water displacing formula worked out. But they must have been really good, because the original secret formula for WD-40®—which stands for Water Displacement perfected on the 40th try—is still in use today.
Convair, an aerospace contractor, first used WD-40 to protect the outer skin of the Atlas Missile from rust and corrosion. The product actually worked so well that several employees snuck some WD-40 cans out of the plant to use at home."
A few years following WD-40's first industrial use, Rocket Chemical Company founder Norm Larsen experimented with putting WD-40 into aerosol cans, reasoning that consumers might find a use for the product at home as some of the employees had. The product made its first appearance on store shelves in San Diego in 1958