I am looking for feedback on CNC machining coolants, we are currently using Hangsterfer's S-500 CF US., but we are in need of more coolant, so we are exploring the other coolants that people may use and if they suit our needs, we machine Stainless Steel, Mild Steel, Aluminum, Brass, Copper and alot of different plastics from Acetal to PVC. This current coolant leaves thick residue on the machines and on the parts if not washed off right away. We keep the refractometer setting from 7 to 9 as per our sales rep suggested. Any suggestions are welcome. Thanks.