在加工工件大圆弧尺寸过程中，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，我厂设计了一种专用测量工具，满足了加工过程和检验的需要。　　一、量具的结构该测量工具结构如图１所示。由基础板１、装表夹具２、定位销４（２件）及千分表３组成，基础板 In the processing of large arc size of the workpiece, the workpiece can not be directly measured due to the irregular shape of the workpiece or the circumference of the arc less than a semicircle (such as a sector). To this end, our factory designed a special measuring tools to meet the needs of the processing and testing. First, the measuring structure The measuring tool structure shown in Figure 1. The base plate 1, the fixture 2, positioning pin 4 (2) and dial indicator 3, the base plate