Many operators don't understand the concept of down milling and up milling. When can down milling be used and when can up side milling be used, we often use up milling to rough machining parts and down milling to finish machining parts. In the machining process of the universal milling machine, down milling and up milling are two words that appear frequently. The milling method in which the direction of the tooth rotation is consistent with the feed direction of the part is called down milling. The direction of the tooth rotation and the part feed are called down milling. The milling method that gives different directions is called up-milling. In the face milling cutter, some end milling, and face milling, the cutting force has different directions. When face milling, the milling cutter is just outside the workpiece, and special attention should be paid to the direction of the cutting force. During down milling, the cutting force presses the work piece against the worktable, and during up milling, the cutting force pushes the work piece away from the worktable. Because the cutting effect of down milling is more ideal, this method is generally chosen. Only when the universal milling machine has thread clearance problems or problems that cannot be solved by down milling, then up milling is considered. Under ideal conditions, the diameter of the milling cutter should be larger than the width of the workpiece, and the axis of the milling cutter should always be slightly away from the centerline of the workpiece. When the tool is placed directly on the cutting center, it is easy to produce burrs. When the cutting edge enters and exits cutting, the direction of the radial cutting force will continuously change. The spindle of the universal milling machine may vibrate and be damaged, the blade may be chipped, and the machined surface will be very rough. The milling cutter is slightly off-center and the cutting force The direction will no longer fluctuate-the milling cutter will gain a preload. We can compare center milling to driving in the center of a road. When the blade performs each cut, the cutting edge must bear an impact load, and the load depends on the chip cross section, workpiece material, and cutting type. When cutting in and out, whether the cutting edge and the workpiece can be properly engaged is an important direction.