Z　5163立式钻床的主电机轴上齿轮采用弹性联轴器与电机轴联接,如附图(a)所示。每次使用不久后,其齿轮根部开裂,迫使更换新齿轮。经分析该齿轮齿根开裂原因:①齿轮齿根壁厚太薄,根据其模数m=3mm、齿数Z=20、修正系数ζ5=　0.34和内孔直径　45mm,进行计算,齿根圆直径为54mm,得壁 The main shaft of Z 5163 vertical drilling machine is connected to the motor shaft with a flexible coupling as shown in the figure (a). Shortly after each use, the root of the gear cracked, forcing the replacement of a new gear. The analysis of the gear root cracking reasons: ① gear tooth root wall thickness is too thin, according to its modulus m = 3mm, the number of teeth Z = 20, the correction coefficient ζ5 = 0.34 and the hole diameter of 45mm, calculated root circle diameter 54mm, too wall