Double helical teeth

Double helical teeth is a teeth that consists of a toothing that makes a “bend” on the face width. It is, as it were, two identical cylindrical gears, 1 x with helical teeth right and 1 x with helical teeth left that imaginary are stuck against each other. The benefit of such gears is that the gears cannot displace axially. The benefits of the helical teeth are retained (quiet tube, larger coefficient of contact); the disadvantages are eliminated (axial forces).