ENB205 Lecture Notes - Lecture 4: Length Measurement, Road Texture, Concentric Objects
Document Summary
Exact dimensions of parts cannot be achieved due to the nature of manufacturing processes. The deviations of dimensions can occur and these deviations must not be so large that the part is useless. Designer specifies upper and lower limits to the dimensions. Tolerance is the difference between the maximum and minimum size limits of a part. Too tight tolerance -> high manufacturing cost. Too large tolerance -> part may not function as expected. Nominal size: it is the designation used for general identification and is usually expressed in common fractions. Basic size of basic dimension: it is the theoretical size from which limits of size are derived by the application of allowances and tolerances. Actual size: the measured size of the finished part. Allowance: is the minimum clearance space (or maximum interference) intended between the maximum material condition (mcm) of mating parts. Minimum hole diameter is taken as the basis, lower deviation for the hole is equal to zero.
