The algorithm and formulas to determine the size of tip relief modification of pre shaving gear hobs are put forward.A principle to determine the lead width of tooth roots is also presented.

• 给出了剃前齿轮滚刀修缘尺寸的计算方法和计算公式，并对滚刀齿根的齿间槽宽提出了更为合理的判断原则。