Two ways of milling cutter rotation direction

The first is down milling. The direction of rotation of the milling cutter is the same as the direction of feed for cutting. At the beginning of cutting, the milling cutter bites the workpiece and cuts off the last chips.
The second is up-cut milling. The direction of rotation of the milling cutter is opposite to the direction of cutting feed. The milling cutter must slide on the workpiece for a period of time before starting cutting. The cutting thickness starts at zero, and the cutting thickness reaches 0 at the end of cutting. maximum.