It is necessary for a hobbing machine to adhere to the direction of motion of the hob teeth and the direction of the gear being cut, but because the hob teeth are placed on a helical line, the direction of the hob teeth is not straight with the hob axis. Therefore, it is necessary for the gear hobbing machine to rotate the tool holder to a viewing point to make it harmonious with the tooth direction of the gear. When rolling and cutting spur gears, the viewpoint of turning is the helix angle of the hob. When hobbing helical gears, the hobbing machine also determines the size and direction of the turning viewpoint based on the helical direction of the helical gear and the size of the helix angle.

When hobbing, it is necessary to adhere to the direction of motion of the hob teeth and the direction of the gear being cut, but because the hob teeth are placed on a helical line, the direction of the hob teeth is not straight with the hob axis. Therefore, it is necessary to rotate the tool holder to a certain viewpoint to make it harmonious with the tooth direction of the gear. When rolling and cutting spur gears, the viewpoint of turning is the helix angle of the hob. When rolling and cutting helical gears, it is also necessary to determine the size and direction of the turning viewpoint based on the helical direction of the helical gear and the size of the helix angle.

The accumulated error of tooth pitch during gear machining is out of tolerance. Improper adjustment or wear of the indexing worm pair on the hobbing machine workbench results in some out of tolerance in the accuracy of the workpiece being machined, which leads to out of tolerance in gear machining. The radial circular runout error and large axial displacement of the hob spindle can also lead to this out of tolerance.