When using cylindrical spiral milling cutters to cut flat surfaces, the following points need to be noted: 1. When installing, the first thing to pay attention to is the spiral direction of the milling cutter. After installation, the reaction force generated by the milling cutter during the cutting process will push the milling cutter towards the spindle along the axis of the cutter shaft. 2. When the surface being milled exceeds the width of the milling cutter, a combination of two cylindrical milling cutters with left and right helical lines is generally used. In this case, we need to pay attention to whether the diameters of the two milling cutters are completely equal; Otherwise, the milled surface will exhibit unevenness. In addition, it is important to clean the side of the milling cutter before installing the cutter shaft. If it is not wiped clean, although the diameter of the milling cutter is exactly the same, there may also be a convex seam in the middle part of the processed surface. At the same time, due to the combination of two left and right helical cylindrical milling cutters, attention should also be paid to the direction and position of the helical lines of the two milling cutters during installation, so that the axial thrust generated by the milling cutters can offset each other. That is to force the two milling cutters to move closer to each other. 3. Whether using straight or helical cylindrical milling cutters, attention should be paid to the rotation direction of the tool shaft before cutting. If the direction of rotation is opposite to the direction of the cutting edge, not only cannot the workpiece be cut, but it will quickly damage the milling cutter.