When milling irregular workpieces and using vises, indexing heads, and special fixtures to hold workpieces, the center of gravity of the irregular workpieces, as well as the vises, indexing heads, and special fixtures, should be placed in the middle of the workbench as much as possible to avoid uneven stress on the workbench and deformation. During fast or automatic feed milling, it is not allowed to move the workbench to two extremes to avoid damaging the screw rod.