Introduce the differential principle of vertical machining center: vertical cnc machining center processing helical gear cylindrical gear requires two movements: one is to generate involute generative movement, this movement is the same as when machining spur gear, namely hob rotation and workpiece Rotational movement; the other is the forming movement that produces the spiral, which can also be decomposed into two parts, namely the linear movement of the tool post and the additional rotation of the workpiece. The motion that produces the spiral is the same as when we turn the thread, that is, in order to form the spiral, when the tool needs to move a lead along the axis of the workpiece, the workpiece must make a full revolution.

When the hob makes one revolution, the cnc machining parts must rotate one tooth (using a single-head hob). In other words, when the vertical machining center forms an involute, the workpiece must rotate, and when the spiral is formed, the workpiece must also rotate; therefore, the rotational movement of the workpiece when forming the spiral must be added to the rotational movement when the involute is formed , That is, the composite rolling helical gears of two rotating motions form an involute and a spiral. The motions are all conforming motions, which are divided into two parts. Each motion requires an internal connection transmission chain and an external connection rotation chain. The inner connection transmission chain that forms the involute is the hob to the workpiece, and the outer connection transmission chain provides power: the motor to the hob; the inner connection transmission chain that forms the spiral line of the vertical machining center is the vertical screw (linear movement) to the Workpiece (rotating motion), this transmission chain is called a differential transmission chain, and the external connection transmission chain is the motor to the lead screw.

Since the formation of the involute requires the rotation of the workpiece, the differential transmission chain of the swiss machining center also requires the additional rotation of the workpiece. These two movements are transmitted to the workpiece at the same time, which will cause the workpiece to interfere. Therefore, a synthetic mechanism must be used in the transmission chain. The differential device is based on the principle of planetary gears, and its requirement is that two inputs are combined into one output, and its ratio is 2:1.