What Are Engineering Drawings?

The abbreviated drawing of the project drawing is called the drawing below to express the projection surface of the object according to the projection method. According to the different projection methods, it can be divided into orthographic and oblique projection. One of the most common engineering drawings is one-dimensional projection, two-dimensional projection, and axonometric projection (stereoscopic projection is also called three-dimensional projection). Drawing frames are required according to Chinese regulations. According to the different drawing frames, they can be divided into Y-type drawings and X-type drawings.

Drawings are technical documents used by the engineering community to accurately express object shapes, sizes, and related technical requirements. In modern times, the design, manufacture, construction, use, and maintenance of all products and equipment such as machines, instruments, and engineering buildings are realized through drawings. Designers express design intentions and requirements through drawings, manufacturers understand design requirements, organize production and processing through drawings, and users understand product structure and performance, correct use methods, and maintenance methods based on drawings. Therefore, drawings as well as words and numbers are one of the important tools for expressing design intent, recording innovative ideas, and exchanging technical ideas. They are known as the technical language of the engineering community, and engineering and technical personnel must be proficient in this language. ^[1]

Engineering graphics take drawings as the research object. In engineering technology, mechanical drawings expressing machines and their parts and civil drawings expressing buildings are collectively referred to as engineering drawings. Engineering drawings can accurately and detailedly represent the shape, size and technical requirements of engineering objects. Drawings are inseparable in mechanical design, manufacturing and building construction. Designers express design ideas through drawings. Manufacturers manufacture, inspect, and debug according to drawings. Users understand structural performance with drawings. Therefore, the drawing is the collection of the whole process information of product design, production and use. At the same time, engineering drawings are also an indispensable tool for engineering and technical exchanges between domestic and international countries, and the technical language of the engineering community.

Today, the information age has given new tasks to engineering graphics. With the development of computer science and technology, computer drawing technology has promoted the development of engineering design methods (from manual design to computer-aided design) and engineering drawing tools (from rulers to computers), changing the thinking and work of engineers and scientists program. ^[2]

Drawing format and format

Frame format

The frame must be drawn with thick solid lines on the drawing, and its format is divided into two types without binding edge (Figure 1.1) and binding edge (Figure 1.2).

Paper size

When drawing drawings, the size of the paper format specified in the figure below should be used.

Title bar

The bottom right corner of each drawing shall have a title bar. The format and size of the title bar shall be in accordance with the provisions of GB 10609-1 1989. It is recommended to use the format shown in Figure 1.3 in the drawing operation.

Under normal circumstances, the direction of the picture is consistent with the direction of the text in the title bar. When the two are inconsistent, the direction symbol can be used to indicate the viewing direction.

proportion

The ratio of the linear size of the figure in the drawing to the corresponding element of the real thing is called the ratio. When drawing the drawing, it should be drawn as much as possible according to the actual size of the parts in a 1: 1 ratio, so that the true size of the parts can be seen from the drawing. Because the size and complexity of the parts are different, the reduction ratio can be used for large and simple parts; the enlargement ratio can be used for small and complicated parts. When drawing drawings in proportion, appropriate proportions shall be selected from the series specified in Table 1.2, and the proportions given in Table 1.3 may also be selected when necessary.

When drawing a drawing, the selected scale should be noted in the title column. When dimensioning, regardless of the enlargement or reduction ratio, the actual dimensions of the parts must be marked.

Each view of the object should choose the same scale as much as possible, otherwise the scale can be marked below or to the right of each view name, such as: BB / 1: 100 and plan view 1: 100.

Font

The Chinese characters, numbers, and letters written in the drawings must be neat: the font is neat, the strokes are clear, the spacing is even, and the arrangement is neat.

The number of the font is the height h of the font.

Chinese characters

The Chinese characters on the drawings should be written in the imitated Song style, and simplified characters officially announced by the state should be used. The characteristics of the long imitation Song style are: the rectangular shape, straight strokes, consistent thickness, clear rise and fall, sharp skimming, and uniform structure. The height h of the Chinese character should not be less than 3.5mm, and the width of the character is generally about 0.7h, as shown in Figure 1.4.

Numbers and letters

Numbers and letters can be written in italics or straight. The italic prefix is inclined to the right, about 75 ° from the horizontal line, as shown in Figure 1.5 and Figure 1.6. When mixed with Chinese characters, you can use straight.

Font application example

The letters and numbers used as indices, scores, footnotes, and size deviations are generally one size smaller than the basic size numbers, as shown in Figure 1.7.

Graph line

When drawing drawings, the lines specified by the national standard shall be used, as listed in Table 1.4. The line width (b) size series is 0.13, 0.18, 0.25, 0.35, 0.5, 0.7, 1, 1.4, 2mm. When using, it is selected according to the size and complexity of the figure. The width of the graph line is divided into three types: thick line, medium thick line, and thin line. The width ratio is 4: 2: 1. In the same drawing, the widths of the same drawing lines should be the same. Thick and medium thick lines are usually selected between 0.5 and 2 mm, and as far as possible, no line with a width less than 0.18 mm appears in the pattern.

On architectural drawings, three line widths can be used, and the proportional relationship is 4: 2: 1; on mechanical drawings, two kinds of line widths, medium thick and thin lines, are generally used, and the proportional relationship is 2: 1. Common line types are: thick solid line, thin solid line, (thin) wavy line, (thin) double-fold line, (thin) dotted line, thick point drawing line, fine point drawing line, etc.

When drawing, it is recommended to use the line specifications listed in Table 1.5, and the line drawing methods are listed in Table 1.6.

Dimensioning

The figure can only express the shape of the machine, and the size of the machine is determined by the dimension of the mark. Dimensioning is extremely important and must be done carefully and meticulously. If the dimensions are missing or wrong, it will cause difficulties and losses to production.

Basic rules

(1) The dimensional value on the drawing should be based on the actual size of the machine, and has nothing to do with the drawing scale and drawing error.

(2) The default unit of dimensions in the drawing is mm (millimeter). If other units are used, it must be specified.

(3) Each dimension of the parts is usually marked only once, and is marked on the graphics that reflect the most clear structural features of the parts.

Size composition

As shown in Figure 1.8, a complete dimension shall generally consist of extension lines, dimension lines, dimension line terminals and dimension numbers.

(1) Extension lines; extension lines are drawn with thin solid lines and should be drawn from the contour, axis or symmetrical centerline of the figure. You can also use contour lines, axes, or symmetrical centerlines as extension lines. The extension line is generally perpendicular to the extension line and can be tilted if necessary. The extension line should be about 2 mm beyond the end of the dimension line.

(2) Dimension line: The dimension line is drawn with a thin solid line and must be drawn separately. It cannot overlap with other graph lines or be drawn on its extension line. When labeling linear dimensions, the dimension line must be parallel to the marked line segment. When there are several dimension lines that are parallel to each other, the spacing between each dimension line should be even, spaced 5 to 10 mm, and the large size should be outside and the small size should be inside. Try to avoid intersections between dimension lines and dimension and extension lines.

(3) Dimensional line terminal: There are two types of arrowhead and oblique line terminal, as shown in Figure 1.9.

The arrows are suitable for various types of patterns. The tip of the arrow is in contact with the extension line, and it must not exceed or leave, b in Figure 1.9 (a) is the width of the thick solid line.

The terminal of the oblique line is drawn with a thin solid line. The direction and drawing method are shown in Figure 1.9 (b), where A is the height of the font. When the dimension line terminal form is adopted, the dimension line and the extension line must be perpendicular to each other.

Only one dimension line terminal can be used in the same drawing. When using arrows, it is allowed to replace the arrows with dots or slashes if the status is not enough.

(4) Dimension figures: Linear dimension figures are generally marked above the dimension line or at the interruption. In the same drawing, a digital annotation form should be used as much as possible. The size of the font should be the same. If the status is not enough, the annotation can be drawn.

The direction of the size figures shall be based on the direction of the drawing. The prefixes of the size numbers in the horizontal direction point upwards, the prefixes of the size numbers in the vertical direction point to the left, and the prefixes of the numbers in the oblique direction should keep the upward trend.

On the drawing, regardless of the direction of the dimension line, the dimension numbers are also allowed to be written horizontally, as shown in Figure 1.10.

Dimension figures must not be penetrated by any drawing line, and when it is unavoidable, the drawing line should be broken.

Dimension annotation example

Table 1.7 lists some dimensional notations specified by the national standard. Figure 1.11 uses the method of right and wrong comparison to point out some common mistakes of beginner dimensioning. ^[2]

Table 1.7

Continued Table 1.7

Continued Table 1.7

Figure 1.11