机械制图 11 轴测图

几何体上的平行于坐标轴的直线段的轴测图,仍与相应的轴测平行;且该线段的轴测图长度是原线段长度与该轴测轴的轴向伸缩系数(简化系数)的乘积。(平行性)Chapter 11 Axonometric ProjectionBeijing Jiaotong University7/29三.轴测图的分类轴测图正轴测图正等轴测图p = q = r正二轴测图p = r ? q正三轴测图p ? q ? r斜轴测图斜等轴测图p = q = r斜二轴测图p = r ? q斜三轴测图p ? q ? r正等轴测图斜二轴测图工程中常用的是:Chapter 11 Axonometric ProjectionBeijing Jiaotong University8/2911-2 正等轴测图一.轴间角与轴向伸缩系数轴向伸缩系数:p = q = r = 0.82轴间角:?X1O1Y1 = ?X1O1Z1 = ?Y1O1Z1 =120°Z1X1Y1O1简化轴向伸缩系数:p = q = r = 1因p2+q2+r2=2用简化系数画出的正等轴测图约放大了1/0.82≈1.22倍。Chapter 11 Axonometric ProjectionBeijing Jiaotong University9/29二.平行于坐标面的圆的正等轴测图平行于H面的椭圆长轴⊥O1Z1轴平行于V面的椭圆长轴⊥O1Y1轴X1Y1Z1 平行于W面的椭圆长轴⊥O1X1轴都是椭圆椭圆可以由圆弧近似拼得Chapter 11 Axonometric ProjectionBeijing Jiaotong University10/29椭圆的近似画法:1. 画圆的外切菱形; 2. 确定四个圆心和半径; 3. 分别画出四段彼此相切的圆弧; 例画平行于H坐标面的圆的正等轴测图近似椭圆画法(四心椭圆法) ●●●●abefdddF1E1●●B1A1●●作图步骤