I. Introduction
The gear-hob was for long time the most productive gear cutting tool. Therefore, it was, and remains a permanent subject of research, these focusing on optimizing the precision and the cutting performance of the gear hob. The gear hob is derived from a basic worm, endowed with cutting properties that are obtained by allocating equiangular disposed, helical, or straight flutes for chip evacuation, and by relieving the addendum and side relief faces. Therefore, repeated resharpening (executed exclusively on the rake face) lead to the decrease of the characteristic diameters, and due to this, the hob cannot anymore reproduce the original worm. Thus, it can be concluded that due to its specific geometry and manufacturing technology, gear hob results with a theoretical profile error. To minimize this, beyond other geometrical restrictions, its top edge constructive rake angle is set to zero. The worm’s helix angle on the pitch diameter, considered as a main parameter, is limited to values smaller that 2°. In case of larger modules, this limit leads to an excessive increase of the pitch diameter. Due to this, helix angle must be increased, and therefore profile correction is needed [1], [2]. In the sources cited before is also considered the possible replacement of the originating involute worm with a straight normal tooth profile endowed convolute worm. Other authors [3], [4] state that the design of a gear hob must start from an involute worm. A detailed systematization and analysis of the gear hob errors is given in [5]. Here different rake face profiles are analyzed using mathematical models. It is shown that profile errors may vanish if the lateral cutting edges are tangent to the base cylinder. This affirmation somehow contradicts the result shown in [6] which demonstrates that even in case of reproducing the perfect involute helicoid of the generating worm, an involute profile error occurs on the machined gear, and this increases with the pitch helix angle of the hob.