There are many methods to modify the helical gear drum shape. At present, there are mainly the following two methods;
One method is more complex, that is, numerical calculation by calculation. This method is accurate and reliable, but the amount of calculation is large, and the final result can only be determined through repeated calculation.
The other method is to investigate and find the previous empirical formula. The drum shape determined according to the seed feeding method usually has specific figures. Its advantages are simple and fast, and its disadvantages are obvious. The empirical formula is not necessarily accurate.

In addition, songlemin of Liming company, a state-owned enterprise in Shenyang, and others designed the drum shape of helical gear according to the equal radius arc method, as shown in the figure. The advantage of this method is that the design method is simple and easy to process. At the same time, problems in the manufacturing process can be found and controlled in the processing process. This method has a wide range of applications.
To sum up, there is no unified method on how to reasonably determine the drum shape of helical gears. As a result, everyone may have different drum shape of helical gears with the same parameter, and the final effect will be different. According to experience, it is recommended to refer to the value of shape modification amount. This method is very limited. The same standard, different effects, can not be unified, so it is more difficult to select. Therefore, it is very important to determine the modification amount by numerical calculation. This paper will study how to establish the mathematical model of shape modification.