Mechanical drawing is the knowledge that factory technicians must master. Some technicians have not learned "mechanical drawing" before, and they can understand processing drawings by seeing more in production. However, it is this unfounded feeling that may cause errors, such as turning the processed parts back. This article summarizes the projection knowledge of mechanical drawing for your reference.

1. Mechanical drawing projection method

According to the projection principle, the shape of the object can be expressed. The object can be placed in any quadrant. Generally, the method of placing the object in the first quadrant to obtain the projection view is called the first angle projection method. Therefore, the second, third, Four-corner projection method.

The four quadrants of space

Click to receive it for free ☞ 10G tutorials on CNC turning (milling), ug programming, cad drawing, CNC simulation, CNC machinery books, etc.

Object and the four quadrants

The views obtained by the second-angle projection method and the fourth-angle projection method overlap, and drawing and reading are not easy, so it is not applicable.

2. The difference between the first angle and the third angle method

The first angle method: the method of obtaining the projected view when the object is placed in the first quadrant, which is called. Master-slave relationship: observer→object→projection surface

First angle method

The third triangle method: when the object is placed in the third quadrant, the projected view is obtained, which is called. Master-slave relationship: observer→projection surface→object

The third method

The first angle method: most of them are used in European countries (such as Britain, Germany, Switzerland, etc.);

The third triangle method: the same direction as we view the position of the object, so the United States, Japan and other countries use this projection method;

The Chinese national standard CNSB1001 stipulates that both the first angle method and the third angle method are applicable, but they cannot be used simultaneously in the same drawing.

In the mechanical drawing, the projection method used is generally indicated by the following icon: