Rules for applying dimensions GOST 2.307 – 68 

Figure 2.1 

Figure 2.2 

Drawing dimensions on a drawing is one of the most important and responsible stages of its execution. It is performed in accordance with the following basic requirements of GOST - 2.307-68:

1. Each dimension is applied only once on the drawing. Repeating dimensions on images or when applying inscriptions is not allowed.

2. The total number of dimensions should be minimal, but sufficient to make it possible to manufacture a product according to this drawing and control the quality of its manufacture.

3. Regardless of the scale, the actual dimensions in millimeters are always indicated on the drawing without indicating the unit of measurement.

4. Dimension lines are limited at both ends by arrows, the ends of which abut against the corresponding line, which is the measurement limit (extension, axial, contour) (Figure 2.1). They are mainly applied outside the image contour. The size of the dimension line arrows depends on the thickness of the visible contour line (Figure 2.2). On training drawings, it is recommended to apply dimension arrows with a length of 5…7 mm.

5. The minimum distance between parallel dimension lines is 7 mm, and between the dimension and contour lines is 10 mm (Figure 2.1).

6. Extension lines are auxiliary. They are drawn from the measurement boundary perpendicular to the straight-line segment of the part element whose size is applied. Extension lines should extend beyond the ends of the arrows or serifs by 1…5 mm (Figure 2.1).

7. Contour, axial, center and extension lines cannot be used as dimension lines. Axial and center lines can be used as extension lines. For this, they must be extended (Figure 2.1). At the same time, it is not recommended to allow the intersection of dimension and extension lines.

8. Dimensional numbers of linear dimensions with different inclinations of dimension lines are placed as shown in Figure 2.3. If it is necessary to indicate the size in the shaded area, then the dimensional number is applied on the shelf - callout (Figure 2.3).

9. Arrows on the diameter of a circle or the radius of an arc must be turned to the line of the circle or arc. Dimensional lines of radii and diameters applied to circles must not occupy horizontal and vertical positions or coincide with center lines.

Figure 2.3

10. Dimensional numbers for radii must be supplemented with a designation according to the pattern R10, R25, where the height of the letter is equal to the height of the number. Dimensional numbers for diameters are supplemented with the conventional sign diametr, which is placed before the dimensional number according to the pattern (Figure 2.1).

11. If there is not enough space between the dimensional arrows when applying the dimensional number, it is applied as shown in Figure 4, placing the number on the right side if possible.

Figure 2.4

12. If there is not enough space for arrows when applying a dimension number, they can be placed on the outside or can be replaced with serifs, which are applied at an angle of 45⁰   to the dimension line along the course of the inscription or with clearly applied dots (Figure 2.5).

13. Conical chamfers made at the ends of cylindrical parts at an angle of 45⁰   are indicated as the product of the leg size and its angle: 2x45⁰. If there are several identical conical chamfers on the drawing of this part, then they are indicated as 2 chamfers 2x45⁰   (Figure 2.6). At other angles of execution of the chamfer, it is indicated as shown in Figure 6 b, that is, the leg size and the angle size are indicated separately.

Figure 2.5

Figure 2.6

14. When applying dimensions, other signs and conventions are also used that allow you to reduce the number of images and sizes.

15. Dimensions are placed according to the principle of an “open chain”, with the exception of construction drawings. A closed chain is allowed if one of the dimensions is indicated as a reference. This dimension is indicated by an asterisk (*), and in the technical requirements it is written: “Dimension for reference” (Figure 2.6, b).

16. Dimension numbers are placed in a checkerboard pattern above parallel or concentric dimension lines (Figure 2.7).

17. When there is not enough space for an arrow due to the close location of the contour line, the latter can be broken (Figure 2.8).

Figure 2.7

Figure 2.8

18. The dimensions of the angle, chord and arc of a circle are applied as shown in Figure 2.9. In the latter case, the sign “Arc” is applied above the dimensional number. Angular dimensions are applied as shown in Figure 2.10. At the same time, for small angles, the dimensional numbers are placed on the shelves of the leader lines in any zone.

Figure 2.9

Figure 2.10

19. If it is necessary to draw the coordinates of the vertex of the rounding angle or the center of the rounding arc, then the extension lines are drawn from the point of intersection of the sides of the rounding angle or from the center of the rounding arc (Figure 2.11).

20. If the view or section of a symmetrical object or individual symmetrically placed elements is depicted only to the axis of symmetry or with a break, then the dimension lines related to these elements are drawn with a break and the break of the dimension line is performed along the axis or along the break line of the object (Figure 2.12a).

21. Dimension lines can be drawn with a break and when depicting the size of the diameters of a circle, regardless of whether the circle is depicted in whole or in part, while the break of the dimension line is performed along the center of the circle (Figure 2.12b).

Figure 2.11

Figure 2.12

21. When depicting a product with a break, the dimension line is not broken (Figure 2.13).

22. Dimensional numbers cannot be divided or crossed by any lines of the drawing. It is not allowed to break the contour line when applying a dimension number and to apply dimension numbers at the intersection of dimension, axial or center lines. Axial, center lines and hatching lines are allowed to be broken (Figure 2.14).

                                                               Figure 2.13                                                    Figure 2.14

23. If, when drawing the size of the radius of an arc of a circle, it is necessary to draw a dimension that determines the position of its center, then it is depicted as an intersection of center or extension lines, and with a large radius, the center is allowed to be brought closer to the arc. In this case, the radius dimension line is depicted with a break at an angle of 90° (Figure 2.15).

24. When the centers of several radii coincide, their dimension lines may not be brought to the center, except for the extreme ones (Figure 2.16).

Figure 2.15 

Figure 2.16 

25. The dimensions of the diameters of a product of complex configuration can be applied as shown in Figure 2.17. In cases where the sphere is difficult to distinguish from other surfaces, the word “Sphere” or the sign according to Figure 2.18 is applied. The diameter of the sphere sign is equal to the size of the dimensional numbers in the drawing.

Figure 2.17 

Figure 2.18 

26. The size of the square is applied as shown in Figure 2.19. The height of the “square” sign is equal to the height of the digits of the dimensional numbers on the drawing.

                                                                               Figure 2.19                                      Figure 2.20 

27. If the drawing contains one image of a part, then the size of its thickness or length is applied as shown in Figure 2.20 and Figure 2.21 

Figure 2.21

28. Product dimensions are always nominal, regardless of the image scale. If an element is depicted with a deviation from scale, then the dimensional number is underlined (Figure 2.22). This rule does not apply to cases when some elements of the image are difficult to draw or it is desirable to increase their visual perception, as well as when depicting thin plates, gaskets, washers in M1:1.

29. Dimension lines are preferably applied outside the image contour, placing the internal and external dimensions of the part on different sides of the image as much as possible (Figure 2.23). However, dimensions can also be applied in the middle of the image contour, if the drawing does not lose clarity from this.

Figure 2.22

Figure 2.23

Conicity

Conicity is the ratio of the difference in diameters of the bases of a right circular cone to its height K=(D–d)/l. ​​

Before the dimension number of conicity, a conventional sign is applied, the apex of which is directed towards the apex of the cone (Figure 2.24)

                                                                                      A)                                                                                              B)

Figure 2.24