The objective of any mechanical product dimensions are conveying to manufacturing and inspection the mechanical engineering needs for the end object. A given object can be dimensioned in various ways and each method should yield the same needs in practice this is true.
Below are the basic steps for mechanical design and drafting services:
Know the needs for the finished mechanical component and its interaction with the next level of assembly.
Work with mechanical design to define datum which are consistent with the functionality of the finished mechanical product.
Define a dimensioning method to suggest the finished part needs.
Identify a tolerancing method which insures the mechanical product will function throughout the range of manufacturing variability.
Do not inquire manufacturing or inspection for more than is absolutely essential to meet the design intent.
Basic Fundamental Rules for Mechanical Design and Drafting
Show enough dimensions so that the intended sizes and shapes can be determined without calculating or assuming any distances.
State each dimension clearly so that it can be interpreted in only one way.
Show the dimensions between points, lines, or surfaces which have a necessary and specific relation to each other or which control the location of other components or mating parts.
Select and arrange dimensions to avoid the accumulation of tolerances that may permit various interpretations and cause unsatisfactory mating of parts and failure in use.
A feature shall not be located by more than one toleranced dimension in any one direction
Where possible, dimension each feature in the view where it appears in profile and where its true shape is evident.
Do not show dimensions to lines representing hidden surfaces.
Where possible, express angular dimensions in degrees and decimal parts of a degree.
Where plus and minus tolerancing is used, the tolerance preference is bilateral and not unilateral.
Equal plus and minus values are preferred.
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