The first is down milling. The rotation direction of the milling cutter is the same as the feed direction of the cutting. At the beginning of the cutting, the milling cutter bites the workpiece and cuts off the last chips.

The second is up-cut milling. The rotation direction of the milling cutter is opposite to the feeding direction of the cutting. The milling cutter must slip on the workpiece for a period before starting to cut, starting with the cutting thickness of zero, and ending at the end of the cutting. The cutting thickness reaches the maximum. The cutting force has different directions in the face milling cutter, some end milling or face milling. When face milling, the milling cutter is just outside the workpiece, and the direction of the cutting force should be paid special attention. During climb milling, the cutting force presses the workpiece toward the table, while in up milling, the cutting force makes the workpiece leave the table.

Because the cutting effect of down milling is the best, down milling is usually the first choice. Only when there is a thread clearance problem on the machine tool or a problem that cannot be solved by down milling, up milling is considered. Ideally, 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 very easy to produce burrs. The direction of the radial cutting force will change continuously as the cutting edge enters and exits the cut, the machine tool spindle may vibrate and be damaged, the insert may chip and the machined surface will be very rough, the milling cutter will be slightly off center, and the cutting force direction will no longer fluctuate - The milling cutter will receive a preload. We can compare center milling to driving in the center of the road.

There are two ways to rotate the milling cutter

Every time a milling cutter insert enters a cut, the cutting edge is subjected to an impact load, which depends on the cross-section of the chip, the workpiece material and the type of cut. When cutting in and out, the correct engagement between the cutting edge and the workpiece is an important direction. When the axis of the milling cutter is completely outside the width of the workpiece, the impact force during cutting is borne by the outermost tip of the insert, which means that the initial impact load is borne by the most sensitive part of the tool. The milling cutter also leaves the workpiece with the tip, that is to say, from the beginning of cutting to the departure, the cutting force acts on the outermost tip until the impact force is unloaded. When the centerline of the milling cutter is exactly on the edge line of the workpiece, the insert is released from the cutting when the chip thickness reaches the maximum, and the impact load reaches the maximum when cutting in and out. When the axis of the milling cutter is within the width of the workpiece, the initial impact load during cutting is carried by the part farther from the most sensitive tip along the cutting edge, and the blade exits the cutting relatively smoothly when the tool is retracted.

For each insert, the way the cutting edge leaves the workpiece when it is about to exit the cut is important. Remaining material near retraction may reduce blade clearance somewhat. As the chips break away from the workpiece, a momentary tensile force is created along the rake face of the insert and often produces burrs on the workpiece. This tensile force compromises the safety of the chip edge in dangerous situations.