The hobbing machine must adhere to the same direction of motion as the teeth of the gear to be cut, but due to the hobbing teeth being located on a helical line, the direction of the hobbing teeth and the axis of the teeth are not straight with the hob. Therefore, it is necessary for the hobbing machine to turn the tool holder at an angle to align it with the tooth direction of the gear. When hobbing, the rotation angle is the helix angle of the hob. When hobbing helical gears, the hobbing machine also determines the size and direction of the turning angle based on the helix direction and helix angle of the helical gear.

When hobbing, it is necessary to maintain the direction of motion of the cutting teeth of the hob in the same direction as the teeth of the gear being cut. However, due to the fact that the cutting teeth of the hob are located on a helical line, the teeth of the hob shaft in the direction of the cutter are not straight. Therefore, it is necessary to rotate the tool holder to an angle that aligns with the tooth direction of the gear. When rolling spur gears, the angle of rotation is the helix angle of the hob. When entering a helical gear, the size and direction of the steering angle must be determined based on the helical direction and helix angle of the helical gear.

The accumulated error of tooth pitch during gear machining exceeds the tolerance range. The indexing worm pair on the hobbing machine workbench is not properly adjusted or worn, which leads to the accuracy of the machined parts exceeding the tolerance, resulting in the accuracy of the machined gears exceeding the tolerance, and the radial circle of the machined gears also exceeding the tolerance range. The large amount of error and axial movement of the hob spindle can also lead to this excessive error.