Flatness and Parallelism: A Comparison
In GD&T the important terms are Flatness and Parallelism as the way of representation is the same as well as the tolerance zone shape is also the same hence these two terms often cause confusion in representing as well as usage.
Navin Baskar·30 Nov 2022·2 min read
Flatness and Parallelism: A Comparison
In GD&T the important terms are Flatness and Parallelism as the way of representation is the same as well as the tolerance zone shape is also the same hence these two terms often cause confusion in representing as well as usage. of these similar symbols
What is a surface flatness in GD&T?
A surface is said to be flat when all of its components are in the same plane.
What is parallelism in GD&T?
A surface, line, or axis that is parallel to a datum plane or axis is said to be parallel.
Differences between surface flatness and parallelism
The common differences under which GD&T symbol these are classified below:
Flatness is classified under form tolerance and by definition, this is a tolerance that does not require a datum that is to be mentioned during the application of the datum. Whereas the orientation tolerance determines the orientation for the form in relation to a reference. It is a geometric tolerance for features related to datums since a datum is always required to express orientation tolerance.
The same concept can be explained using a block where one by one flatness and parallelism are applied.
Consider a table on which the same is applied to a work table:
The above figure represents how parallelism is implied in the part.
Here the floor surface is my datum reference and the tolerance is applied to the top of the table which is marked using the chained line. We have applied the parallelism hence we can see that with res[ect to the Datum the tabletop is parallel as well as it is flat.
To explain the fatness case try removing one leg of the table and we can see that the surface is no more parallel to the datum surface and is also inclined but the flatness of the table top is still the same as shown in the figure:
Hence from the above, we can conclude that if parallelism is given it also makes sure that the correct shape is maintained and in the case of flatness it doesn't make sure the shape is maintained any flat plane orientation is accepted for flatness throughout the plane.
