The main recommendation is to use as much milling as possible.
When the cutting edge is just cutting, the chip thickness can reach its maximum value in the down-cut milling. In the case of up-cut milling, it is the minimum value. In general, tool life in up-cut milling is shorter than in down-cut milling because the heat generated in up-cut milling is significantly higher than in down-cut milling. When the chip thickness is increased from zero to maximum in up-cut milling, more heat is generated because the cutting edge is subjected to a higher friction than in the down-milling. The radial force is also significantly higher in up-cut milling, which has an adverse effect on the spindle bearings.
In down-cut milling, the cutting edge is mainly subjected to compressive stress, which is much more advantageous for cemented carbide inserts or solid carbide tools than for the tensile forces generated in up-cut milling. of course there are exceptions. When using a solid carbide end mill for side milling (finishing), especially in hardened materials, up-cut milling is preferred.
This makes it easier to obtain wall straightness with a smaller tolerance and a better 90 degree angle. If there is a misalignment between the different axial passes, the tool marks are also very small. This is mainly due to the direction of the cutting force. If a very sharp cutting edge is used in the cutting, the cutting force tends to "pull" the knife toward the material. Another example of the use of up-cut milling is the use of old-fashioned manual milling machines for milling, where the screw of the old-fashioned milling machine has a large gap. Up-cut milling produces a cutting force that eliminates the gap, making the milling movement smoother.