Milling processing involves metal cutting with high-speed rotating tools to remove material. A horizontal machining center is a machine tool that achieves milling processing through a structure with a horizontally arranged spindle. Due to the horizontal arrangement of the spindle, the tool reciprocates along the workpiece side to effectively expel chips. Horizontal machining centers can also be equipped with a dual-changeover worktable for unattended operation and to shorten the workpiece processing cycle.