What is General Tolerance? All you need to know
General tolerance is a concept used in engineering and design to simplify the specification of tolerances for dimensions. Instead of assigning specific tolerances to every dimension on a drawing, general tolerances are used to make the workflow faster while ensuring high quality of the final product. In this article, we’ll discover of what is general tolerance and explore how it sets itself apart from other tolerance types.
Difference between Dimensional Tolerances and General Tolerances
Dimensional tolerances are used for dimensions that require specific precision and are explicitly expressed, such as 100±0.1, to convey the designer’s intention clearly as the tolerance values can be arbitrarily determined.
General tolerances, on the other hand, allow for bulk specification of the tolerance range for individual dimensions, reducing drawing effort and enhancing clarity on the drawing.
What are the Grades of General Tolerances?
The choice of grade becomes significant when using general tolerances. In JIS (Japanese Industrial Standards), there are four grades: . These tolerances are further subdivided based on, for example, dimension types, including length dimensions, chamfer dimensions, angle dimensions, perpendicularity.
While the values for general tolerances are determined based on their grade, they can differ depending on the component’s dimension. For example, 1±0.1 and 100±0.1 have the same tolerance range, but when considering the ratio in relation to length, the difference in precision becomes 100 times greater. Therefore, JIS manages dimension precision uniformly by setting tolerance values for each division of standard dimensions within the drawing.
When you check the above tolerance table, you can see that
the tolerance values change based on the reference length. For instance, for an
18mm dimension in the fine grade, it automatically specifies a tolerance of
±0.1 without the need to note dimension tolerances on the drawing.
When applying general tolerances to a drawing, indicate the general tolerance along with the grade in the title block of the drawing.
Common Use of Tolerance Grades:
Fine Grade: Precision metal parts for precision machinery, etc.
Medium Grade: Common metal parts, etc.
Coarse Grade: Common resin molded parts, etc.
Summary
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