What is Engineering Tolerance, Types And Fit?

DALIAN, China - Jan. 24, 2022 - PRLog -- What Is Engineering Tolerance?

Engineering tolerances are the allowable deviations in measurements derived from basic measurements.

Assume that a 100 mm metal rod is processed. Even though all the steel bars are intended to be processed into the same shape, due to the size and direction of the steel bars, not all the steel bars can be manufactured to an accuracy of 100.00 mm. Although the design and manufacturing sites have been working hard to reduce such deviations, they still cannot be controlled to zero.

This size and shape deviation basically fluctuates up and down around the target value. Therefore, the upper limit value and the lower limit value of the upper limit value relative to the target size are determined based on the use of the metal rod. The difference (allowable range) between these two values is called "tolerance".

Tolerances can be applied to many different units. For example, working conditions may have tolerances for temperature (°C), humidity (g/m3), etc. In mechanical engineering, the tolerances we mainly talk about apply to linear, angular and other physical dimensions. Regardless of the unit, the tolerance indicates the acceptable measurement range from the base point (nominal value).

Engineering Tolerance Types

Engineering tolerances include dimensional tolerances, shape tolerances and position tolerances.

Dimensional Tolerance

The dimensional tolerance is the allowable amount of change in the size. This is the basis of engineering tolerances. The maximum allowable value is called the maximum size. The minimum value is called the minimum dimension.

Tolerance is the absolute value of the algebraic difference between the maximum upper limit size and the minimum upper limit size, and the absolute value of the algebraic difference between the upper deviation and the lower deviation.

Lower Deviation

Adding a lower deviation tells the manufacturer how much a certain measurement value can be smaller. This is indicated by the "-" symbol.

Upper Deviation

The upper deviation is the opposite of the lower deviation. Add it to show how much larger the measured value can be than the nominal value.

Bilateral Deviation

The third way to give a tolerance range is to use a bilateral deviation.

In the case of the same basic size, the smaller the dimensional tolerance, the higher the dimensional accuracy. The specified tolerance indicates the requirement of manufacturing accuracy and reflects the difficulty of processing.

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