Basic Concept Of Dimensional Chain
There are two characteristics of the dimensional chain: closedness-each size of the dimensional chain constitutes a closed system in a certain order; correlation-one of the size changes will affect other size changes.
The component ring that changes in the same direction as the closed ring is called an increased ring, that is, when the size of the component ring increases (or decreases) and the other component rings remain unchanged, the closed ring also increases (or decreases), as shown above D in a; n The component ring that changes in the opposite direction to the closed ring is called a reduced ring, that is, when the size of the component ring increases (or decreases) and the other component rings remain unchanged, the size of the closed ring decreases (Or increase), as d in the figure a above.
Classification of dimensional chain
- 1 Divided by application: assembly dimension chain, part dimension chain, process dimension chain.
- 2 According to the spatial position of each ring: linear dimension chain, planar dimension chain, spatial dimension chain. A common dimensional chain is a linear dimensional chain. The plane dimensional chain and the spatial dimensional chain can be converted into linear dimensional chain by the coordinate projection method. n According to the geometric characteristics of each ring size: length dimension chain, angle dimension chain.
- 3 This chapter focuses on the linear dimension chain in the length dimension chain.
In the dimension chain line diagram, the line segment with a single arrow is commonly used to indicate each ring, and the arrow only indicates the direction of searching the dimension chain to form a ring. The ring with the same direction as the arrow of the closed ring is the decreasing ring, and the ring with the opposite direction of the arrow of the closed ring is the increasing ring.
The parts shown, according to the dimensions A1 and A3 noted in the drawing, are not easy to measure during processing. Now they are processed according to the dimensions A1 and A2. To ensure the original design requirements, try to calculate the basic size and deviation of A2.
According to the title, according to the size A1, A2 processing, A3 must be a closed ring, A2 is the process size.
Then the basic size of the closed ring is 50-10 = 40mm
Lower deviation is 0
The upper deviation is -0.06-(-0.36) = + 0.30mm
There is no specific algorithm written above, so I will summarize it for everyone.
The opposite direction to the closed ring is the increasing ring, otherwise it is the decreasing ring.
The basic size of the closed ring is equal to the sum of the basic sizes of all the increasing rings minus the sum of the basic sizes of all the reducing rings
The upper deviation of the closed loop is equal to the upper deviation of the increasing loop minus the lower deviation of the decreasing loop
The lower deviation of the closed loop is equal to the lower deviation of the increasing loop minus the upper deviation of the decreasing loop
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