Geometries of milling cutter

However, a positive rake tool is weaker than a negative tool, and the hardness of the workpiece material and its surface condition may dictate use of negative rake cutters. Negative rake tools generate greater cutting forces and higher cutting temperatures.

The geometry of the cutting edges themselves initiate and control the cutting action and cutting forces, and thereby affect the generation of heat. The edge of the tool where it meets the workpiece can be chamfered, rounded or sharp. Chamfered or rounded edges are stronger, but once again produce higher cutting forces and more heat. A sharp edge, while not quite as strong, reduces cutting forces and runs cooler.

The T-land behind the cutting edge directs the chip and can be positive or negative, with the same tradeoff of lower operating temperatures for the positive design against the stronger but higher-heat-generating negative arrangement.

Because the cutting action in milling is interrupted, chip control features of milling tools generally are not as important as they are in turning. However, depending on the workpiece material and arc of engagement involved, the energy involved in forming and directing the chip can be significant. Tight or hard-breaking chip control geometries immediately curl the chip and generate higher cutting forces and heat. More open chip control geometries produce lower cutting forces and operating temperatures, but may not be appropriate for use with some combinations of workpiece material and cutting parameters

Cooling questions
Manipulating coolant application is another way to manage temperatures generated in metalcutting operations. Excessive temperatures cause a cutting edge to wear rapidly or deform, so heat must be controlled as quickly as possible.

To lower temperatures efficiently, cooling has to be directed to the source of the heat. However, it is extremely difficult, if not impossible, to inject coolant into the high-temperature cutting zone where pressure between the chip and cutting edge is in the neighbourhood of 20,000 bar. In addition, coolant evaporates instantly in such a severe environment. Coolant may not be fully effective in removing heat in such a situation, but it may help to some extent.

Exactly how much difference a stream of coolant makes is unclear; coolant effectiveness is a subject on its own. It is like a religion; you believe in it or you don’t. In general, if excessive heat is anticipated, coolant can be applied. In slot milling, for example, coolant use generally will not be harmful. It can help but how much is a subject for discussion. In side milling, however, where cutting temperatures can remain low, it is probably best not to apply coolant.