机械制图立体的投影（2）

　　今天我们学习《机械制图》——立体的投影第二部分的内容。今天的主要内容是平面与平面立体表面相交。Today we are studying Mechanical Drawing - Projection of the three dimensions part 2. Today＂s main topic is the intersection of a plane with a flat three-dimensional surface.
　　No. 1 平面立体的截交线与断面
　　1.截交线的概念：平面与立体表面的交线，称为截交线。
　　2.断面的概念：当平面切割立体时，由截交线围成的平面图形称为断面。
　　3.平面立体的截交线是截平面上的一个平面多边形，它的顶点是平面立体的棱线或底边与截平面的交点，它的边是截平面与平面立体表面的交线。
　　1. The concept of intersection line: the intersection line between the plane and the three-dimensional surface, called the intersection line.
　　2. The concept of a section: when a plane cuts a three-dimensional, the plane figure enclosed by the intercept line is called a section.
　　3. The intercept line of a plane cubic is a plane polygon on the intercept plane, its vertex is the intersection of the prism or bottom edge of the plane cubic with the intercept plane, and its side is the intersection line between the intercept plane and the surface of the plane cubic.
　　No. 2平面立体的缺口
　　在形状较为复杂的机件上，有时会见到由几个平面与平面立体切割而形成的具有缺口的平面立体，只要逐个作出各个截平面与平面立体的交线，并画出截平面之间的交线，就可作出具有缺口的平面立体的投影图。In the more complex shape of the machine, sometimes seen by several planes and planes of three-dimensional cut and formed by the plane with the gap of three-dimensional, as long as each cut plane and the plane of three-dimensional intersection line, and draw the intersection line between the cut plane, you can make the projection of the plane with the gap of three-dimensional.
　　No. 3两平面立体相贯
　　两个或多个立体相交（也称为两个或多个立体相贯）形成的形体，称为相贯体，立体表面的交线，称为相贯线。相贯体是一个整体，将相贯体看作两个或多个立体相交，仅是在对相贯体各部分的形状和相对位置进行分析时的一种假设。
　　两立体相贯有两平面立体相贯，平面立体与曲面立体相贯，两曲面立体相贯三种情况。两平面立体的相贯线通常是一组或两组闭合的空间折线，折线的每一线段都是两立体各一个平面表面的交线，每一个折点都是一个立体的棱线或底边与另一个立体表面的交点。因此，只要分别作出一个立体的诸平面表面与另一个立体的平面表面的交线，就可连续成两立体的相贯线。
　　A form formed by the intersection of two or more dimensions (also known as the intersection of two or more dimensions) is called a coherent body, and the line of intersection of the three-dimensional surfaces is called the coherent line. The coherent body is a whole, and to consider the coherent body as the intersection of two or more dimensions is only an assumption in the analysis of the shape and relative position of the parts of the coherent body.
　　There are three types of three-dimensional coherence: two planes of three-dimensional coherence, two planes of three-dimensional coherence with curved surfaces, and two curved surfaces of three-dimensional coherence. The coherence of two planes is usually a set or two closed sets of spatial folds, each segment of which is the intersection of a plane surface of each of the two dimensions, and each folding point is the intersection of the prism or bottom edge of one dimension with the surface of the other. Thus, by making separate lines of intersection between the planar surfaces of one dimension and the planar surfaces of the other, the lines of intersection of the two dimensions are continuous.
　　No. 4平面立体的穿孔
　　在形状较为复杂的机件上，有时会见到平面与平面立体相交而形成的具有缺口或穿孔的平面立体。In the more complex shapes of the machine, it is sometimes possible to see flat surfaces with notches or perforations formed by the intersection of flat surfaces with flat surfaces.
　　参考资料：文字：百度；图片：微博；翻译：百度翻译
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