Basic Worm Gear Hob
The blades on both sides of the gear hob are the intersection line between the front and the surface of the lateral blade, which should be distributed on the surface of the worm screw, which is called the basic worm of the hob. There are three basic worm types:
1.The flank of the helical tooth of the involute worm is an involute helix, and the intersection line of the tangent plane and the involute helix is a straight line, and the end profile is an involute. The intersection line between the axial section of involute worm and the asymptotic spiral surface is a curve. The hob made of this basic screw has no design error of tooth profile and high precision of cutting gear. Manufacturing hobs, however, is difficult.
2.The flank of the spiral tooth of the Archimedes worm is the surface of the Archimedes spiral. The cross line between the spiral plane of the worm and the spiral plane of the Archimedes worm is a straight line. The hob made of this basic worm is simpler and more convenient to manufacture and examine than involute worm. But there is a slight tooth form error. However, this error is within the allowable range, for this reason, most of the basic worm of finishing hob are replaced by the Archimedes worm.
3.The tooth profile of normal profile worm profile is straight line and the end profile is extension involute. This kind of basic worm replaces the involute basic worm as hob, and its tooth profile design error is large, so it is generally used as large modulus, multi-head and rough machining hob.