Taking cordierite and topaz for example, the specific cone-apexAngle values are given, and the reason why the cone-apex angles are too small is analyzed.
并以堇青石和黄玉为例给出了具体的锥顶角数值大小，分析了锥顶角很小的原因。
2
Rotating the disc of the compound rest with an angle equal to half the apexangle of the cone.