After the pretreatment of the end face spiral gear is completed, the next task is to establish the coordinate system. The establishment of coordinate system is the basis of all 3D modeling, because all features in the later stage are generated based on the coordinate system established at this time. At the same time, the establishment of coordinate system is also the difficulty of accurate reverse engineering modeling. The coordinate system is different from the actual features, and there are often no entities. For example, the coordinate system of rotating parts often contains an axis, and the accuracy of the axis can only be determined by the cylindricity of the selected rotating surface. If a rotating body contains multiple rotating surfaces, there may be a great deviation between the final parts generated by selecting coarse datum and fine datum during modeling. Accurate reverse engineering modeling of end face spiral gear requires modelers to master a certain degree of processing and design experience, and the coordinate system generated after selecting the appropriate benchmark can be closer to the original coordinate system of the real object.
After the coordinate system is established, start to select the plane for patch fitting. The first is to fit the teeth of end face spiral gear. There are three ways to fit the teeth of end face spiral gear. The first is to fit all the end face spiral gear teeth one by one. This fitting method takes a long time. Although it can restore the scanned object to the greatest extent, considering the machining error of the entity and the error generated in the process of patch fitting, the cumulative error of the final modeling may have a large deviation from the design value. The second is to establish a solid model of teeth and then array them. This fitting method takes a short time and the circumferential pitch of the model is good, but the final fitting effect depends on the accuracy of the array reference axis and the selected tooth model. Considering that modeling one by one is not conducive to the control of design parameters, the array method is selected for modeling. In order to avoid the machining defects of the selected teeth and improve the accuracy of modeling, we select 6 teeth from the middle spacing of the end face spiral gear teeth, and conduct surface fitting and array on the tooth surfaces on both sides of the end face spiral gear teeth one by one. Finally, by comparing the final deviation results of each array, The end face spiral gear teeth with the smallest comprehensive deviation are selected as the samples of the array. The fitting effect is shown in the figure.