I had a 4,000 square foot machine shop for nearly 40 years, sold it and retired; rust was not a problem in the good old days when coolants had amines in them to prevent breakdown and consequent rusting. The scare over nitrosamines forced the removal of amines; after reformulating, rust was a big problem, especially on machines that were used infrequently, where tramp oil would prevent the coolant from being aerated and breakdown occurred . I had a large surface grinder where this was a regular event, and I did try bubbling air into the sump without much success. I have a power hacksaw in my home shop where rust is a big problem, it cements the fine chips into a solid mass that takes a hammer and chisel to break up. My plan with it is to use a 50/50 mixture of cutting oil and kerosene, as recommended by the maker of the Marvel power hacksaw that is in my old shop. The kerosene transmits heat better than oil, the cut off parts are quite noticeably cooler than when the oil is concentrated. I plan to also use this on my Brown & Sharpe universal mill at home. On most of my machines at home I use TapFree in a tuna can with a brush, in my lathe, a Regal Leblond 19", I use a modern coolant concentrate that does not seem to have so much potential for rust as the previous ones that I have tried; oil, when used for roughing makes way too much smoke, which I imagine does not do good for our lungs.
