几何形状位置公差中英对照21-27.doc

基准（续） 目标基准点 目标基准点用X形状符号表示，由两根相交90度的直线组成。符号显示标注在应用表面的平面图上（见下图的A面）。当平面视图上不可见时，符号可显示标注在两相邻视图上（见下图B面）。用基本尺寸定位基准目标点相对其他基准目标点和零件上其他基准的位置。 21 Datums (Cont.) Datum Target Point A datum target point is specified by an X-shaped symbol, consisting of a pair of lines intersecting at 90o. The symbol is shown and dimensioned on the plan view of the surface to which it is being applied (see panel A of the figure below). Where this type of view is not available, the symbol can be shown and dimensioned in two adjacent views (see panel B of the figure below). Basic dimensions should be used to locate datum target points relative to each other and the other datums on the part. 21  基准（续） 目标基准线 下图举例说明了定义目标基准线的3种方法：（A）平面图上的投影线，（B）X形状标在表面的边视图上，（C）综合前两者的方法。用基本尺寸定位目标基准相对其他目标基准和相关基准之间的位置。 在量具中，经常用量具销的侧边模拟基准目标线，下图举例说明了如何用量具来模拟目标基准线。 22  Datums (Cont.) Datum Target Line Figure below illustrates the three ways to specify a datum target line: a phantom line on the plan view of a surface, (B) an X on the edge view of a surface, and (C) a combination of a phantom line and an X. Basic dimensions should be used to locate the datum targets relative to other targets and datums. A datum target line is often simulated in a gage by the side of a gage pin. The figure below illustrates a gage for simulating a datum target line. 22基准（续） 基准目标区域 有3种方法指定基准目标区域。对于目标基准A，通过在零件表面绘出检具轮廓来模拟目标基准区域，并标注在图纸上。轮廓用虚线表示 ，阴影线填充，如下图A所示。区域形状，尺寸和位置用基本尺寸来描述。如果目标区域是圆形，在基准目标符号的上半部分指定直径，如下图B所示。对于圆形目标区域，可以在零件表面上显示“X”，在基准目标符号里标出直径大小，如下图C所示。 23 Datums (Cont.) Datum Target Area There are three ways to specify a datum target area. A datum target area is designated by drawing the outline of the gage for simulating the datum target area on the part surface. The outline is shown in phantom lines, and the shape is crosshatched as shown in panel A. the shape, size, and location of the area are described with basic dimensions. If the target area is circular, the diameter may be