SECTION 3.2
The Cooler the Better

At 33 surface feet per minute (SFPM) and a 0.003" rise per tooth (feed rate), cutting edge temperatures are measured at 400°C [750°F]. At 100 SFPM, temperatures rise to 600°C [1112°F]. These temperatures are not conducive to good tool life. Poor tool life will occur if there are poor techniques for reducing or preventing high temperatures at the cutting edge.

Now, consider the empirical equation for tool life. It automatically follows that if we had a coolant which removed heat better, reduced friction more, and more effectively cooled the tool, we would improve tool life. It is that simple, but let's examine some physical problems.

In an attempt to support this theory, refrigerated coolants have been used. Messrs. Boston, Gilbert, and McGee observed tool wear with applied coolant temperatures of 40°F to 150°F for both a water soluble and an oil. The best results, strictly in terms of tool life, were at 40°F with oil. But, at temperatures of 150°F, the soluble gave better tool life. Another scientist, named Palitzch, was not happy with these results as he felt the varying viscosity of the oil confused the results. He worked with compressed air at various temperatures and had the same results. The conclusion? The cooler the better!