What is the best coolant for broaching?

A water soluble cutting oil mixed at a manufacturer’s recommended concentration (often 10-12%) is the best coolant for a broaching application. In some applications, a straight cutting oil provides a better surface finish, but has less heat capacity. Broaching applications usually require a cutting fluid designed for heavy duty machining applications. Often, a cutting fluid designed for general turning or milling applications does not contain enough lubricating elements to provide acceptable performance in broaching applications.