浅析第三角画法图样的表达特点及识图方法

A Brief Analysis of the Expression Characteristics and Reading Methods for the Third Angle Projection Drawings

机械图样中第三角画法的投影原理和第一角画法相同,但因其观察视线与投射线方向相反,而且其投影面的翻转方式与第一角画法也大不相同,在图样表达上还有一些独特的表达习惯和规定,这些都给我国工程技术人员的读图带来了较大困难。本文在查阅大量外文文献资料的基础上,总结出了第三角画法的一些常见的表达形式,并分析了第三角画法图样的识图方法,以供我国工程技术人员参考。

In mechanical drawings, although the projection principles of the first angle projection and the third angle projection are identical, it is very difficult to read the third angle projection drawings for our engineering and technical personnels. In the third angle projection drawings, the observing line of sight and the projecting line of the objects toward the projection plane are in the opposite direction, the developing manner of the projection planes is quite different from the fist angle projection, and there are a lot of unique expression habit and rules.The three factors mentioned above take difficulties to read the third angle projection drawings.Based on consulting a large number of foreign literatures, some common expression forms in the third angle projection drawings have been summarized, and the reading methods of the third angle projection drawings have also been analysed. Then references have been presented for the engineering and technical personnels in our country.