在机加工过程中 ,对工件大圆弧尺寸精度的加工及检验 ,往往由于工件异形或圆弧圆周小于半圆（如扇形）而无法直接测量。为此 ,我们设计了一种专用工具 ,满足了在加工过程中测量和检验的需要。１结构如图１所示 ,基础板为一小型平板 ,先设定其纵向中心线 ,再设定零线与纵向中心 In the machining process, the machining and inspection of the precision of the large arc size of a workpiece often can not be directly measured because the shape of the workpiece is irregular or the circumference of the arc is smaller than a semicircle (such as a fan shape). To this end, we have designed a special tool to meet the needs of the process of measurement and inspection. 1 structure shown in Figure 1, the basic plate for a small flat panel, set its vertical centerline first, then set the zero line and vertical center