Since the reform and opening up, my country has introduced a lot of foreign equipment, drawings and other technical data, and many developed countries have different projection methods for mechanical patterns from those used in my country. In order to better learn the advanced technology of developed countries, it is necessary to quickly understand foreign mechanical drawings.
1. Overview
In today's world, ISO international standards stipulate that the first and third angle projections are equally effective. Countries have their own priorities according to their national conditions. Among them, Russia, Ukraine, Germany, Romania, Czech Republic, Slovakia, and Eastern Europe mainly use first-angle projection, while the United States, Japan, France, Britain, Canada, Switzerland, Australia, and the Netherlands Countries such as Mexico and Mexico mainly use the third angle projection. Before the liberation, our country also adopted the third angle projection, after the founding of the People’s Republic of China, it switched to the first angle projection. Third-angle projection is often encountered in imported foreign mechanical drawings and scientific books. The ISO international standard specifies the projection marks for the first and third corners (Figure 1 and Figure 2). In the title bar, there are marked symbols. According to these symbols, the drawing method can be recognized, but some drawings have no projection marks.
Figure 1 The first angle drawing mark symbol
Figure 2 The third triangle drawing mark symbol
2 The third triangle projection
The space can be divided into eight areas by the front plane V, the horizontal plane H, and the side plane W, which are the first, second, third, fourth, fifth, sixth, seventh, and eighth sub-angles, as shown in the figure 3 shown.
picture
2.1 Putting the object in the first angle projection is called the first angle projection, also known as the E method-the European method.
2.2 The projection of the object in the third angle is called the third angle projection, also known as the A method-the American method.
Our country uses the third angle projection method.
The third triangular projection is an imaginary method of placing an object in a transparent glass box, using each side of the glass box as the projection surface, and making orthographic projections according to the position of the person, face, and object to obtain graphics, as shown in Figure 4 and Figure 5.
Figure 4 and Figure 5
2.3 The position of the six basic views in the third triangle projection
The ISO international standard stipulates that the positions of the six basic views in the third angle projection are shown in Figure 6.
Figure 6
The above view is obtained by projecting the object onto each projection surface of a closed rectangular (transparent) "projection box".
Each view can be understood as: when the observer's line of sight is perpendicular to the corresponding projection plane, the actual image of the object he sees.
The front view is the front projection of the object obtained by the observer assuming that he is in front of the object and moving his eyes point by point, and the line of sight is always perpendicular to an imaginary upright projection surface (transparent). Other views can be similarly used. get.
The reader should always treat the view as a side of the object itself. From the front view, you can see the height and width of the object, as well as the positions of the top, bottom, left and right sides of the object. The top view shows the depth and width of the object.
2.4 Advantages of the third triangle projection
(1) The view configuration is better for easy identification
The viewing direction is directly reflected between the views, which is convenient for viewing and drawing. The left view is on the left and the right view is on the right. And the first angle projection sometimes uses the "view" to make up for the unclear parts.
(2) It is easy to imagine the spatial shape of objects
The left and right views are facing inward, and the top view is facing downwards, so that it is easy to imagine the shape of the object.
(3) It is convenient to draw the side view
It is easy to imagine the spatial shape of an object, which directly helps to imagine the shape of the object when drawing an axial diagram.
(4) Conducive to expressing details of parts
Neighboring diagrams are arranged nearby, and generally do not need to be marked separately, as shown in Figure 7.
Figure 7
(5) The size and other annotations are relatively concentrated.
3 Comparison of the line width of some major countries (Table 1)
4. Introduction to mechanical drawing standards of several countries
4.1 American Standard (ANSI)
The United States only requires the use of the third angle projection (occasionally, the first angle projection is also used on architectural drawings and structural drawings, but it must be specified).
There are two types of view layout, the first is the same as the ISO international standard, as shown in Figure 6. The second is shown in Figure 8.
Figure 8
The dimensioning method in the American standard: the dimensions in the American drawings are rarely measured in mm, generally inches (1 inch = 25.4mm). Originally, the number of inches expressed in fractions, such as 9/16 inches, etc., was changed after 1966 Decimal, written in decimal form. When the value is less than 1, do not write 0 before the decimal point, and the number is recommended to be written horizontally. For the upper and lower deviation of the tolerance size, pay attention to the same number of decimal places as the basic size, such as or. For sizes above 6 feet, the inch symbol, such as "12'7", should be indicated.
(1) Diameter, radius, spherical code
① When the view is clearly reflected as a circle, the diameter code DIA (diameter) or D is not noted, as shown in Figure 9; when there is only one non-circular view, the diameter code DIA or D is added after the size number, as shown in Figure 10.
Figure 9
Figure 10
②The radius code R (radius) is not added after the radius size number. When the radius size is marked in the view that does not reflect the radius and the real shape of the arc, the code TRUER (TRUE RADIUS) (true R) is required after the radius size number. . For the sphere code, add the code SPHER DIA (ball diameter) or SPHERR (SPHER RADIUS) (ball radius) after the size number.
(2) The injection method of chord length (CHORD) and arc length (ARC) is shown in Figure 11.
Figure 11
(3) Chamfer CHAM (CHAMBER) as shown in Figure 12.
Figure 12
(4) The counterbore is shown in Figure 13.
Figure 13
(5) The keyway is shown in Figure 14.
Picture 14
(6) The thread mark is shown in Figure 15.
Figure 15
4.2 Japanese Standard (JIS)
The drawing representation method is similar to that of the United States. Generally, the third-angle projection method is used. In principle, the first and third-angle drawing methods should not be mixed in the same drawing. If necessary, the two drawing methods can be mixed locally, but the arrow must be used to show the other The projection direction of a painting.
Dimensioning method in Japanese standard:
(1) Code of diameter, radius, square, sphere
When there are diameter, radius, square or spherical diameter and radius in the figure, add "φ", "R", "□" before the size number. When the figure is clear, φ, R, □ can be omitted.
(2) Chamfer
Generally the same as our country, the 45° chamfer can be indicated by the letter "C", as shown in Figure 16, C2 is equivalent to 2×45°, and C3 is equivalent to 3×45°.
(3) When the plate thickness is not drawn, the letter "t" can be added, as shown in Figure 16, t10, which is equivalent to δ=10 in my country.
(4) Use "P" to indicate the rivet hole spacing, such as: P=100, P=98 (indicating that the hole spacing is 100 or 98).
(5) The size of the hole can indicate other content after the number
① Blind hole, as shown in Figure 17. The description of the processing method is usually marked after the size number, such as 深サ (indicating depth), キソ (indicating drilling), etc.
②The thread drawing method is similar to that of our country, and its marking form is shown in Figure 18.
4.3 British Standard (BS)
The view expression method is basically the same as the ISO international standard, and the dimensioning method is basically the same as that of my country's national standard (GB). The unit is also mm. There is a gap (about 1mm) between the size lead line and the outline. In the cross-sectional view, some draw a section line, and some do not draw a section line.
4.4 French Standard (NF)
The view expression method is basically the same as the ISO international standard, and the dimensioning is basically the same as that of my country.
4.5German (mainly referring to the former Federal Germany) standard (DIN)
The view representation method is basically the same as the ISO international standard. In the view projected as a circle, there is only one arrow on the dimension line, and Φ is added after the size; if there are two arrows, "Φ" is not noted. Other size notation can be understood.
4.6 Russia and other CIS national standards (ГОСТ)
The view expression and dimensioning are basically the same as in my country.
Others such as: Canadian standard (CSA), Polish standard (PN) and ISO national standard standards are also similar.
