圆弧样板的半径,一般是在“大工显”或“万工显”上用“弓弦法”进行测量的。当被测圆弧的轮廓有形状误差时,“弓弦法”往往不能反映被测圆弧半径的实际状况。再者,被测半径相同时,弦长和弓高越小,半径误差越大。所以“弓弦法”不适应那些大半径圆弧样板的测量。为了提高大半径圆弧样板的测量精度,本文推荐一种在“万工显”上用“旋转法”测量 The radius of the arc model is generally measured in “Daxiangxian” or “Gongxianxian” by “bowstring method”. When the contour of the measured arc has a shape error, the “bowstring method” often can not reflect the actual state of the measured arc radius. Furthermore, the same measured radius, the smaller the chord length and bow, the larger the radius error. Therefore, the “bowstring method” does not adapt to those large-radius arc template measurements. In order to improve the measurement accuracy of a large radius arc model, this paper recommends a “rotation method”