Metal cutting operations live on a narrow line between friction and heat. Too little lubrication and the chip rubs, welds, or tears against the tool. Too little cooling and heat builds in the tool, workpiece, and fluid, pushing dimensions, finish, and tool life out of control. Yet adding more of one does not automatically improve the other. A richer fluid may lubricate well while insulating the cutting zone; a leaner, faster-flowing fluid may carry heat away while leaving the tool without enough film strength. The balance is not a single recipe. It changes with the material, the operation, the tool coating, the machine, the finish requirement, and the downstream cleaning…