The standard tolerance is specified by the national standard and is used to determine any tolerance of the width of the tolerance zone, which is represented by the "international tolerance" symbol "1T".
(1) The standard tolerance level determines the level of dimensional accuracy, which is called the standard tolerance level and is represented by Arabic numerals. According to the regulations, the standard tolerance of CNC machine tools is 20 grades, namely Ⅱ01. rro.rrl, ….IT17. IT18. The IT01 level of CNC machine tools is the highest, and the following are in descending order. When it forms the tolerance zone together with the letters representing the basic deviation, the CNC machine omits the letter "IT", such as F7, h6, etc.
(2) Standard tolerance value Standard tolerance value.
The standard tolerance value determines the width of the tolerance zone corresponding to each standard tolerance level of each basic dimension segment. Although it belongs to the standard tolerance of the same tolerance level, the numerical value corresponding to each basic dimension segment of the CNC machine tool is different, that is, the width of the tolerance band of each segment of the CNC machine tool Widen as the base size increases, but they are still considered to be equally accurate.
The tolerance class of dimensions without tolerances is specified as IT12. IT18, the length is specified as {ITo When necessary, the CNC machine tool can use ±÷IT (ie Js or Js) regardless of holes and axes.