How do up milling and down milling primarily differ?

Up milling and down milling are two distinct methods of milling that primarily differ in the direction of the cutter's rotation relative to the feed of the workpiece. In up milling, also known as conventional milling, the cutter rotates against the direction of the feed. This means that as the cutter engages with the workpiece, it starts to cut from the top surface and moves downward. This creates a thicker chip at the beginning of the cut, gradually reducing the thickness as the cut progresses, which can lead to a higher cutting force initially and greater wear on the tool.

Choosing the correct answer highlights a fundamental aspect of up milling—where the cutter's rotational speed is indeed opposite to the direction in which the workpiece is fed. This principle is vital for understanding how cutting forces, tool wear, and chip formation vary between the two milling methods.

On the other hand, other options suggest characteristics of milling that do not accurately define the differences:

• Describing how the workpiece moves past the tool does not capture the core distinction between the two methods.

• Stating that the cutter rotation in down milling is opposite to the feed direction is incorrect, as it actually moves with the feed direction.

• The notion of down milling using a stationary cutting tool is inaccurate,