Upper deviation(also called upper limit deviation) refers to the upper limit dimension minus itsBasic dimensionsThe algebraic difference obtained.The upper deviation of the hole is represented by ES, and the upper deviation of the shaft is represented by es.
Dimensional deviation(Deviation for short) refers to the algebraic difference between a certain dimension and its basic dimension.Maximum limit dimensionSubtractBasic dimensionsThe algebraic difference obtained is called the upper deviation;The algebraic difference of the minimum limit size minus its basic size is calledLower deviation。The upper and lower deviations are collectively referred to asLimit deviation。The deviation can be positive, negative or zero.[1]
Represented in the figure
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Fig. 1 Schematic Diagram of Tolerance Zone
As shown in Figure 1, the upper deviation of the hole and shaft isTolerance zone diagramIs shown in Figure 1.
relationship
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Basic deviation, refers to the deviation near the zero line.When the tolerance zone is above the zero line, the basic deviation is the lower deviation;When the tolerance zone is below the zero line, the basic deviation is the upper deviation (Figure 2).
Fig. 2 Schematic Diagram of Basic Deviation[2]
Basic deviation code
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Figure 3 Basic deviation code
The basic deviation code is expressed in Latin letters, with 28 holes in uppercase and 28 shafts in lowercase.As shown in Figure 3 and Figure 4.
In Figure 3, there are 21 basic deviations represented by one letter, which is from 26 Latin letters, and is easy to be removed from other Latin letters
It is formed after I, L, O, Q, W (i, l, o, q, w) with mixed meanings, and it is specified that capital letters represent the basic deviation of holes;The lower case letters indicate the basic deviation of the shaft.There are 7 basic deviations represented by two letters. Among the basic deviations represented by two letters, CD (cd), EF (e1) and FG (fg) are basic deviations of intermediate nature.If the basic deviation of CD is between C and D, the purpose is to reduce the gap between two adjacent basic deviation values, so as to meet the needs of precision machinery and watch industry with the size below 10mm.The other three two letter basic deviations are ZA (za), ZB (zb) and ZC (zc) because they are specified after the basic deviation of Z (z).Its purpose is to meet the requirements of large interference fit
Yes, but the tolerance zone of the basic deviation of JS (js) is completely symmetrical across the zero line, and its upper and lower deviation values are ± IT/2.The tolerance zone of the basic deviation J (j) is approximately symmetrical to the zero line. Since the basic deviation of JS (js) that the tolerance zone is completely symmetrical to the zero line is specified, the standard only retains the basic deviation J in three tolerance classes for holes, and the basic deviation j in four tolerance classes for shafts.The basic deviation H and h are both zero, but the former is the lower deviation and the latter is the upper deviation.Obviously, the tolerance zone determined by the basic deviation of H is the tolerance zone of the datum hole;The tolerance zone determined by the basic deviation of h is the tolerance zone of the datum axis, and they offset the upper and lower sides of the zero line respectively.Therefore, the standard stipulates that the reference hole shall take H as the code;The datum axis takes h as the code.
The position of the tolerance zone determined by each basic deviation is shown in Figure 4.It can be seen from Figure 4 that part of the basic deviation of the same letter between the hole and the shaft is symmetrically located on each side of the zero line.The basic deviation of the shaft from a to h is the upper deviation CS. Except that h is zero, the rest are all negative values. For the same nominal size, its absolute value gradually decreases;From j to zc is the lower deviation ei, most of which are positive values. For the same nominal size, their absolute values gradually increase.For the single L, the basic deviation from A to H is the lower deviation EI, and J to ZC is the upper deviation ES, whose sign and absolute value are basically the same as the basic deviation of the shaft
contrary.Since the position of the other limit deviation of the tolerance zone changes with the level of tolerance, the other limit deviation position of each tolerance zone in Figure 4 is drawn as an opening form, which is to be determined.[3]
