Mechanical marking size
1. Basic rules
(1) The dimension (unit: mm) in the drawing does not need to indicate the code or name of the unit of measurement. If other units are used, the corresponding measurement unit or name must be indicated. The extension line is drawn with a thin solid line, usually the extension line of the contour line, axis or symmetrical center line of the figure, which is about 2 ~ 3 mm beyond dimension line. You can also directly use the contour line, axis or symmetrical center line as the dimension boundary. Extension lines are usually perpendicular to dimension line and can be tilted if necessary.
(2) dimension line and dimension line draw with thin solid lines, which must be drawn separately and cannot be replaced by other lines. Generally, they should not overlap with other lines or be drawn on their extension lines. And should try to avoid the intersection between dimension line and dimension line and the extension line. Dimension line should be parallel to the marked line segment, and the dimension line spacing marked in parallel should be uniform, and the spacing should be greater than 5mm, and the dimension line spacing in the same drawing should be equal.
When marking the angle, dimension line should be drawn as an arc with the center of the circle as the vertex of the angle.
(3) dimension line terminal dimension line terminal has two forms, arrow or diagonal. As shown in figure 1-9. Arrows are suitable for various patterns. When the dimension line terminal is in the form of thin diagonal, the dimension line must be perpendicular to the extension line. Only one dimension line terminal can be used in the same drawing. When using arrows, dots or diagonal lines are allowed to be used instead when the position is not enough. (4) Size Number The number of linear size is generally written above dimension line or at the breakpoint of dimension line. No drawing line can pass the dimension number, otherwise the drawing line should be disconnected.
2. Examples of various sizes
(1) Numbers with linear dimensions should be written in the direction shown in Figure1-1a, that is, the prefix in the horizontal direction is upward, the prefix in the vertical direction is left, and the prefix tends upward when tilted.
(2) When the angle is marked by the angle and dimension marking method, all dimensions and numbers are written horizontally, that is, the prefix is always upward, and it is generally marked at the dimension line break.
(3) Pay attention to the dimensions of circle, arc and ball.
[1] When a circle or an arc larger than a semicircle is marked, the symbol "φ" should be added before the size number; When marking arc radius, the symbol "R" should be added before the dimension number. Dimension line should pass through the center of the circle and end with an arrow.
[2] When the arc radius is too large, it is impossible to mark the position of the center of the circle within the drawing range, and only a part of dimension line can be drawn.
[3] When marking the diameter or radius of a sphere, an "s" should be added before the symbol "φ" or "r".
(4) Note method of small size For small size, when there is not enough space to draw arrows or write numbers, you can draw the arrows outside, or use a dot instead of two arrows, or you can use marginal notes or quotation marks to mark the size numbers.
(5) Marking chord length and arc length The dimension boundary between chord length and arc length should be perpendicular to the middle vertical line of the chord. When dimensioning arc length, dimension line should use an arc, and the symbol "⌒" should be added above the dimension number.
(6) Marking methods of other structural dimensions
[1] dimension line should be parallel to the line connecting the two intersections. ⑵ The thickness of plate-shaped parts with square structure and injection-molded plate-shaped parts can be marked with symbols before the size figures.
T. When the cross section of machine parts is marked with square structural dimensions, the symbol □ or "side length × side length" can be added before the number of side length dimensions.
[2] Injection method of uniformly distributed group structure. The evenly distributed group structure is marked by one of them, and the size label is composed of "number × size (evenly distributed)". When the positioning and distribution of the group structure are clear, the angle can be omitted and the word "evenly distributed" can be omitted.