GD&T Parallelism
Mufaddal Rasheed 
What is meaning of Orientation control of Parallelism in GD&T ? what is the interpretation on the drawing?
If a feature has to be controlled with respect to the degree of parallelism with respect to another surface which is the datum reference then the orientation control of parallelism is used in GD&T
Here is an example of a simple block.
The feature control frame says that the surface pointed at should be within a tolerance zone of 0.02 mm with respect to its parallelism with respect to datum A which is the bottom surface.
Parallelism inspection:
- The component to be inspected when placed on the gauge block .
- The bottom surface of the part is datum feature and corresponding contacting surface on gauge block is called as the datum feature simulator .
- A dial indicator is moved across the surface which has to be inspected.
- The level of the dial indicator is adjusted as per the basic dimensions of the part
- If the variations + or – are beyond the tolerance zone then part is not acceptable in parallelism.
Parallelism vs Flatness:
Consider these two drawings one with parallelism and the other with flatness form control
- Both have same tolerance zone shape
- But Flatness of surface is with respect to itself whereas parallelism is with respect to another datum feature – bottom surface
- Even if the top surface is not parallel to primary datum A but can still be flat
- Manufactured part in which top surface is flat but not parallel to the datum
Another example of application of Parallelism in part drawing:
Parallelism has been applied to a feature of size which is the width (nominal 20) with respect to the axis of the hole.
Tolerance zone definition for parallelism control:
Learn more about how to Interpret GD&T callouts from this Free e-book on GD&T interpretations
To learn more about GD&T have a look at this course
Geometric Dimensioning and Tolerancing: Basics
Explore more topics in GD&T :
What is virtual condition in GD&T
Factors in Specifying tolerance
GD&T Regardless of feature size
GD&T maximum material condition
What is datum feature modifier
What is actual mating envelope
What is 3-2-1 principle in tolerancing
Applying GD&T scheme to a bracket
GD&T applied to patterns of features
Tolerance stack up analysis of a simple part
What are material conditions in GD&T
Composite position tolerance in GD&T
What are datum targets in GD&T
Verification of manufactured GD&T drawing
What are simultaneous requirements in GD&T
Calculating the geometric tolerance of a part
Developing GD&T scheme for a part
Traditional tolerancing vs GD&T
Categories: : GD & Tolerancing
