Requirements of dimensioning in engineering surveying and mapping

Methods and requirements for dimensioning on surveying and mapping drawings;

(1) When dimensioning, you should start from the datum part.

(2) The dimensions on the mapping drawing shall be marked according to the general rules stipulated in the national standards for mechanical drawing. Numbers in vertical direction can be written straight, just like numbers in horizontal direction. Generally, the two sides are equal in size, so you can not draw them. If the positions of two adjacent dimensions are very narrow, you can draw a small point on the boundary of the dimension; If there are many continuous dimensions, you can also draw a short line at the intersection of the dimension line and the extension line instead of two connected arrows. The scale on the map is estimated and can't be very accurate. But the proportion and size of each part should be as symmetrical as possible.

(3) When dimensioning, dimensioning should be done according to the parts processing procedure. Because the size on the drawing will directly affect the processing procedure and working time. Therefore, when drawing any part, the position of the reference part should be determined first, that is, the measured size should be measured according to the processing procedure of the part, and the dimensions should be marked according to the measurement order.

Finally, we should talk about the matters needing attention in dimensioning. Summarized as follows:

1. When dimensioning, it is necessary to consider whether the dimensioning meets the technological requirements of parts processing;

2. Two parts are connected and matched with each other in the same size, and their positions and values must be consistent, so as to avoid assembling the processed parts;

3. The tolerance dimension marked on the mapping must be consistent with the surface smoothness of the reference surface. For example, the basic size of a workpiece is 50 mm, which requires 2-level accuracy, and the allowable deviation of the size is 0.008 mm The final processing procedure of this workpiece is rough grinding, and the surface finish should be marked with 6.3.

4. The dimensional deviation of the parts should be marked according to the mechanical equipment and technical level of the workshop, and the surface accuracy of the parts should be marked according to the requirements of the parts themselves, that is, their role in assembly, otherwise surveying and mapping is unrealistic and uneconomical.