What methods are mainly used to draw mechanical samples?

When the machine tool projects on the projection plane, there are two relative positions between the observer, the machine tool and the projection plane: the machine tool is located between the projection plane and the observer, which is called the first angle projection method; The projection plane is located between the machine part and the observer, which is called the third angle projection method. Both projection methods can perfectly express the shape of machine parts, and ISO standard stipulates that both drawing methods can be used. The national standard of our country stipulates that the first angle projection method should be adopted. In this projection method, the main view is placed in the main position of the drawing, the left view is placed on the right side of the main view, and the top view is placed below the main view. If necessary, you can also draw views in other directions in the spare part of the drawing. In order to express the internal structure of the machine more clearly, we can imagine cutting the machine with a cutting plane, removing the part between the observer and the cutting plane, and projecting the rest onto the projection plane to get a sectional view. Section lines (thin 45 solid lines) should be added to the solid part in the section view. For some complex structures, such as threads, gears, splines, springs, etc. They can be represented by the diagram specified in the standard. The breadth, format, proportion, font and lines of mechanical drawings shall be implemented in accordance with the provisions of national standards. In order to make the parts more stereoscopic and intuitive, sometimes an axonometric drawing with oblique parallel projection is drawn. Traditional mechanical drawing is done by drawing pencil on the drawing board with the help of T-square, triangle and drawing instrument. With the development of electronic computers, various computer-aided drawing softwares have been developed. With the help of plotter, not only can all the work of mechanical drawing be carried out by man-machine dialogue, but also the graphics can be enlarged, reduced, translated and rotated at will as needed, which greatly improves the efficiency and quality of mechanical drawing.