At present, all gear hobs are Archimedes, and the basic worm is Archimedes worm. This kind of hob is similar to involute hob, so the theoretical error value of approximate modeling is very small and can be ignored. Because Archimedes hob is easier to manufacture than involute hob, stock is widely used.
At present, there are two kinds of materials commonly used for pitchgear hob: high speed steel and cemented carbide. High speed steel hobs are widely used in the processing of general steel and non-ferrous gears. As the gear is increasingly made of high strength, high hardness and stainless steel, the high-speed steel hob can not meet the needs of processing, so the carbide hob is gradually widely used. The use of carbide hob can increase the amount of hobbing chips, prolong the tool life, improve the tooth surface finish and ensure the stability of dimensional accuracy of parts.
The main difference between the small module gear hob and the medium and large module gear hob is that the chip holding groove is a straight groove. Generally, the chip holding groove of gear hob should be spiral and perpendicular to the spiral line of hob. In this way, both sides of the cutter teeth can obtain equal front angle and teeth
The shape angle makes the cutting conditions of both sides of the cutting edge consistent when cutting, and makes the tooth shape of the workpiece processed symmetrical. However, the grinding of the spiral groove edge is troublesome, and it is easy to produce errors that make the cutting edge of the cutter tooth separate from the basic worm helicoid and affect the accuracy of the gear to be machined. It is easy to cut because of its small helix angle.