机械图样是用正投影的方法绘制的。正投影的基本性质有实形性、积聚性、类似性。直线或平面对投影面有三种位置,即平行、垂直、倾斜。物体上平行于投影面的平面,其投影反映实形;平行于投影面的直线的投影反映实长,我们称之为实形性。物体上垂直于投影面的平面,其投影积聚成一条直线;垂直于投影面的直线的投 Mechanical drawings are drawn using orthographic projection. The main features of orthographic projection are realism, accumulation and similarity. Linear or plane projection plane has three positions, that is, parallel, vertical, tilt. The object is parallel to the projection plane, the projection reflects the shape; parallel to the projection of the projection of the surface reflects the real length, we call it real. Objects on a plane perpendicular to the projection surface, the projection of a straight line; projection perpendicular to the projection of the surface of the vote