AutoCad 20
Unit 9 - Tolerance
Because of time constraints, we will not be spending much time in Tolerancing. Nevertheless, tolerancing is an important aspect of engineering design. Below you will find a brief introduction to tolerancing. Please read this section carefully.
There will not be any projects for this unit. However there will be a short (1 class) tutorial on Tolerncing in which you will be given the opportunity to practice tolerancing techniques in AutoCad LT. You must attend this tutorial before progressing to the next unit. |
The sizes of parts shown on a drawing are directly related to where and how the part fits into the product for which it is intended. If a part must fit against it or into another part, both parts must be dimensioned to a size that permits them to be assembled.
Most products are made of parts that are built in different factories. When these parts are assembled at a central location, any one must fit into the assembly. In other words, the parts must be interchangeable.
To ensure that parts are interchangeable, their sizes are toleranced on the engineering drawings. Tolerancing means that each dimension is allowed to vary in size within a specified range. The size of the tolerance depends on the degree of precision needed for the surface being dimensioned.
Each dimension on each part is tolerenced. Dimensions that are not critical to the final assembly have a general tolerance. The general tolerance is given on the drawing with a note or in supplementary documents. Such a note might read:
TOLERANCE ± 0.01 UNLESS OTHERWISE SPECIFIED
Often the general tolerance is shown in the title block. Parts that must join, called mating parts, usually have closer tolerances. These are applied directly to these dimensions.