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Dimensioning Rules In Mechanical Drawings

Dimensioning Rules In Mechanical Drawings
Issue Time:2019-08-26

Dimensioning Rules In Mechanical Drawings

Basic rules

1. The actual size of the machine should be based on the size of the size noted on the drawing, regardless of the size of the graphic and the accuracy of the drawing.


2. The dimensions of the drawings (including technical requirements and other instructions), in mm, do not need to indicate the code or name of the unit of measurement. If other units are used, the code or name of the corresponding unit of measurement must be indicated.


3. The dimensions indicated in the drawings are the final dimensions of the parts shown in the drawings, otherwise they should be further explained.


4. Each dimension of the machine is generally only marked once and should be marked on the graphic that reflects the clearest structure of the structure.

Size composition

As shown in the figure below, a complete size should generally include size numbers, dimension lines, extension lines, and arrows or diagonal lines that indicate the end of the dimension line.

Size composition of bearing drawing

1, size figures

Linear size numbers should generally be written above the dimension line and also allowed to be written at the break of the dimension line.


2. Size line

Dimensional lines are drawn with thin solid lines and cannot be replaced by other lines. Generally, they must not coincide with other lines or draw on their extension lines. When dimensioning a linear dimension, the dimension line must be parallel to the dimensioned line segment; when there are several parallel dimension lines, the large dimension should be outside the small dimension to avoid the dimension line intersecting the dimension line. When dimensioning a circle or radius on a circle or arc, the dimension line should generally pass through the center of the circle through the center of the circle or extension. The terminal of the dimension line has two forms, as shown in the figure: the arrow is applicable to various types of patterns, b in the figure is the width of the thick solid line; the oblique line is drawn with a thin solid line, and h in the figure is the font height. The end of the circle diameter, arc radius and angle dimension line should be drawn as an arrow. When using the slash form, the dimension line and the extension line must be perpendicular to each other.

Size line of bearing drawing

3. Dimension line

The dimension line is drawn with thin solid lines and should be drawn from the outline, axis, or centerline of the symmetry of the graph. It is also possible to use a contour line, an axis or a symmetrical center line as the extension line. The extension line should generally be perpendicular to the dimension line and should be about 2 mm beyond the end of the dimension line.

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