The principle of axial displacement method: (1) when the hob moves along the cutter bar, the thread of cutter teeth must be continuous to form a “lengthened hob” with enough length and integrity to ensure that the gear has correct tooth profile. (2) the cutting end of the hob starts to roll from the point that first hinders the “engagement” of the hob, that is, to cut off the beginning of the length direction of the alveolar metal, and then gradually move the hob along the axial direction of the tool bar to make the effective tooth of the hob cut to the end of the required length of the enveloping tooth profile, so as to obtain the correct tooth profile and smooth rolling. It is not easy to move the hob to and fro, which is time-consuming and inconvenient to measure. Therefore, in order to facilitate the operation in production, the method of hob “centering” or special cutter pad is used to move the hob axially with the reference point.
The hob “centering” method can be used to find the offset datum point. The so-called hob “centering” requires that the symmetrical line of a cutter tooth or groove in the middle of the hob passes through the center of the gear blank, so that the center line of the gear blank can be found, and the axial offset datum point of the hob can also be found, so as to meet the design purpose of super large modified gear and find the offset datum point conveniently, no matter whether the gear accuracy is normal or not It is required that the hob should be “centered”. When the standard hob is used to cut the super large modified gear, the hob should be “centered”, and it can be used for the gear hob with handle and sleeve; or the isosceles triangle method with the diameter of the rotary table of the gear hobbing machine as the bottom edge should be used, and then the apex point should be engraved on the tool holder with “■” as the symbol as the reference point.
There is a simple way to judge, that is, the point where the cutting end of the hob and the tooth blank first obstruct the “meshing”. This point is the starting point, and the distance from the point to the datum point is the length of the metal cutting off the tooth groove.
After hobbing, the hob moves I (I = 1,2,3) axial pitch along the axial direction, so that the cutter teeth with larger wear leave the maximum load area, while the cutter teeth with smaller wear move to the larger cutting load area at the other end, and the correct tooth profile can be obtained by segmented hobbing. It and hob “axial shifting” have the same thing that hob moves axially, but the direction is opposite, and their functions and purposes are different, so it is called standard hob axial shifting method. This method is mainly based on two basic requirements that the minimum length of hob should meet. Firstly, the cutting amount of the maximum load area is cut off, and then it moves a distance axially into the enveloping tooth length area. After several cycles, the whole gear is enveloped.