What is the meaning of the form control Straightness? When called out how to interpret it?
Straightness is a form control in GD&T . When applied to a surface , straightness basically controls the variation of each of the lines with respect to their peaks and valleys .
Here is an example of a block on which straightness is applied.
The line segments are inspected for variation from highest points to lowest points.
From the crest to the trough .
Tolerance zone is a 2 D rectangle with a width of 0.02 .
Each cross section of the surface is checked for straightness.
Inspecting planar surface straightness involves running probes or dial gauge indictors across the line segments of the surface as shown . The total indicator reading is taken m if it exceeds 0.02 for any instance then the surface is not acceptable in straightness.
When Straightness applied on a cylindrical surface the meaning remains the same but instead of a flat surface the surface is cylindrical.
Shape of the tolerance zone is still the same a 2D rectangle with width of 0.5 mm.
The inspection using dial gauge indicator :
Axis straightness
Axis straightness is a special type of straightness control . When straightness feature control frame is attached to the size dimension , it is said that axis straightness is being controlled.
Here is an example :
Tolerance zone definition is different in this case .
It’s a cylinder with a dia of 0.5
The fact that it’s a cylinder is indicated by the dia symbol .
Straightness in two directions is also a way of controlling straightness in perpendicular directions as shown in the views below :
The tolerance values can change if straightness in one direction is to be controlled more tightly as compared to the other.
Learn more about GD&T 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