In a complex assembly, there are lots of parts that must work in a very good relationships between them. This relationships between parts can be done by producing them with specified tolerances and dimensions. Parts in an assembly generally have physical contact between them to work properly. These physical contacts are adjusted with tolerances and dimensions of the parts. If you want to work youe assembly or mechanism in the desired way, you need to design individual parts with required dimensions and tolerances. Also producing parts in these dimensions and tolerances is an another tough business in manufacturing.
If we take a look at the definition of ‘dimension’ term in ANSI; ‘‘a numerical value expressed in appropriate units of measure and indicated on a drawing and in other documents along with lines, symbols, and notes to define the size or geometric characteristic, or both, of a part or part feature.’’ The definitions is very straightforward that you need to give the dimensions of designed part in an appropriate way with the language of engineering called as ‘technical drawing’. There are bunch of rules to show ‘dimensions’ of parts in technical drawings.
But in manufacturing of that designed part, dimensions of that part can not be produced accurately as in technical drawing. There are always deviations of defined dimensions at technical drawing in manufacturing phase. So you need to define the ‘tolerances’ of each dimensions of parts for its production in manufacturing processes. Tolerances defines the boundry of these deviations around the exact dimension that defined at technical drawing.
ANSI definition of ‘tolerance’ terms says; ‘‘the total amount by which a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits.’’. So you understand that the maximum limit must lie upon the exact dimension and the minimum limit must lie below the exact dimension of part that defined in technical drawing. Also there are bunch of definition rules of tolerances of a part dimensions in technical drawing language around engineers.
The basic definitions of tolerances of parts and dimensions of parts in technical term can be explained like above. Leave your comments and questions about ‘dimensions of parts’ and ‘tolerances of parts’ below!