锥形螺纹平均螺旋升角的计算

在万工显上，采用影像法测量圆锥形外螺纹的诸参数（例如：牙距、牙形半角等）时，中央显微镜的立柱要倾斜一个角度。与测量普通的圆柱形外螺纹不同的是，该角度是一个平均值，称为平均螺旋升角。给出了平均螺旋升角的三种计算公式及其推导过程。

The Calculation of Mean Spiral Angle with Conical-shaped Thread

In the universal tool microscope, there would be tilted at an angle for the column of the central microscope by using image method to measuring the parameters (for example: pitch, half of thread angle etc.) of conical outer thread. And the difference from measuring the common cylindrical outer thread is that the angle called the mean spiral angle is a mean value. The three kinds of calculation formulas with their derivation processes for the mean helix angle are introduced.