Basic knowledge of mechanical drawing recognition

Basic knowledge of mechanical drawing recognition

1. Concept of mechanical drawing (1) Engineering Drawing: in engineering technology, the drawing drawn for engineering construction or product manufacturing according to the projection method and the provisions of national standards is called engineering drawing, which is referred to as drawing for short

◆ engineering drawings can be divided into: mechanical drawings, architectural drawings, hydraulic engineering drawings, etc

(2) mechanical drawing: it is specialized in studying the theory and method of drawing mechanical drawing. It is the most basic technical document in production; It is the basis for designing, manufacturing, inspecting and assembling products; It is an engineering language for scientific and technological exchanges. Its main content is a set of machine views drawn by orthographic projection method, as well as the dimensions and technical requirements required for processing and manufacturing

2. Projection

(1) basic concept of projection

◆ when an object is illuminated with light or sunlight, it will produce shadows on the ground or wall. This phenomenon is called projection

◆ orthographic projection: when the projection rays are parallel to each other and perpendicular to the projection plane, the projection of the object on the projection tensile testing machine is used to test various conductor planes used in the project, which is called orthographic projection

(2) three side view: refers to the general name of the main view of the object on the orthographic projection plane, the top view on the horizontal projection plane and the left view on the side projection plane

◆ front view: it shows the shape and length of the object from the front to the rear, the size in the height direction, and the positions in the left, right, up and down directions

◆ top view: it shows the shape, length, size in the width direction and the positions in the left, right and front and rear directions of the object

◆ left view: it indicates the shape and width of the object viewed from the left to the right, the size in the height direction, and the positions in the front, back and up and down directions. 3. Drawing viewing angle

(1) viewing angle defines the drawing method: two forms: the first viewing angle and the third viewing angle

◆ ISO international standard stipulates that in expressing the structure of mechanical parts, the first angle and the triangular projection method are equally effective

China's 100% production of chemical coke focuses on the first angle drawing method (Britain, Germany, etc.), while our company focuses on the third angle drawing method (the United States, Japan, Hong Kong and Taiwan funded enterprises)

◆ definition of perspective

the first perspective: the method of making the graphics obtained by orthographic projection according to the relative position of human (observer) - object (machine) - plane (projection plane)

the third angle of view: it is a method of making a figure obtained by orthographic projection according to the relative positional relationship between man, face and object

(2) angle of view example identification

◆ first angle of view:

◆ third angle of view:

(3) view of the third triangular projection

◆ when each projection plane of the third triangular projection method is expanded, it is the same as the first angular projection method, stipulate that the V plane does not move, and rotate other projection planes to form a plane with the V plane

◆ the expanded top view is located above the front view, and the right view is located to the right of the front view

◆ the names of the six basic views obtained by the triangular projection method are: front view, top view, right view, rear view, bottom view and left view

(4) name and configuration of the first corner and the third triangular view

(5) comparison of the two projection methods

◆ similarities

-- the views drawn by the two projection methods are the projection planes obtained by orthographic projection on three mutually perpendicular projection planes

-- expand the projection planes, both stipulate that the V plane does not move, and rotate the H plane and W plane to form a plane with the V plane, so the long alignment and high level are still maintained between the views in the third triangular projection, Projection law of equal width

◆ differences

-- the first corner projection is to place the object between the observer and the projection plane, that is, the figure figure figure

-- the third triangle projection is to place the projection plane between the observer and the object, that is, the person figure and object. And generally pay more attention to some basic configurations of the experimental machine. It can be assumed that the projection plane is transparent and the view is obtained by the observer looking at the object through the transparent projection plane