Sunday, 2 September 2018

International tolerence (IT) grade

          IT Grade refers to the International Tolerance Grade of an industrial processes defined in ISO 286. This mechanical tolerence grade identifies what tolerences a given proces can produce for a given dimension.
The specific tolerence for a particular IT grade is calculated by the following formula
Where :
               . T is the tolerence in micrometers {µm}
               . D is the geometric mean dimension in millimeters [mm]
               . ITG is the IT grade, a positive integer.

The larger the ITG, the looser the tolerence that can be achieved.

          Almost all manufacturing processes have an IT grade associated with, indicating how precise it is. IT grade offer guidence for typical manufacturing method capability or how precise one can expect manufacture of a specific option or feature.
          When designing a part, an engineer will typically determine a key dimention (D) and Tolerence on that dimension. Using this formula, the engineer can determine what IT Grade is necessary to produce the part with those specifications. For example, if injection molding has an IT Grade of 13 and a part needs an IT Grade of 5, one cannot injection mold that part to those specifications. It is useful in determining the processes capable of producing parts to the needed specification.

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