When the rake face of the chip holding groove is unevenly distributed relative to the center of the inner hole after the grinding of the gear hobbing hob edge, the cumulative error ∆ t Σ of the peripheral pitch of the chip holding groove will be generated,
As shown in the figure. The accumulated error of the circumferential pitch of the groove will make the chip edge of the gear hobbing hob deviate from the position of the basic worm helical surface, and the tooth thickness of the hob teeth is not equal. When hobbing the gear, the phenomenon of “over cutting” or “Empty Cutting” of the blade will occur, resulting in tooth profile error, as shown on the right in the figure. The third cutter tooth has the maximum negative deviation, the cutter tooth is thickened, resulting in “over cutting” (i.e. more cutting allowance), while the tenth cutter tooth has the maximum positive deviation, the cutter tooth is thinned, resulting in “Empty Cutting” (i.e. less cutting allowance), resulting in linear error of the tooth shape, i.e. obvious edges on the tooth surface.
When the gear hobbing hob has accumulated pitch error after grinding, it can be seen from its indexing cylinder expansion surface, that is, from Figure 1 that there will be a maximum axial offset (i.e. BC in Figure 2) between the two cutter teeth with the maximum deviation (i.e. 3 teeth and 10 teeth in Figure 1).
It should be pointed out that the above axial offset ∆ T1 of the cutter occurs simultaneously on a row of blades along the axis direction of the same cutter tooth. Therefore, it does not affect the axial pitch error of the gear hobbing cutter, but only the position of the left and right edges of the cutter tooth.