control in GD&T can be a surface Straightness of a feature
or an axis Straightness of a cylinder. If the axis straightness
is called out, it is usually called out with an (MMC) maximum
of a surface
can be used on a feature to control the flatness without
refer to a datum. Straightness only measures the variance
on a straight line. In the following example, straightness
is only called out on the surface of the feature, the height
differences are measured to see how flat or straight the
line is along the indicated surface.
along axis in GD&T, the maximum
material condition ( MMC ) is
commonly called out together to ensure both the diameter and
it axial straightness are controlled.
: Cylinder of OD 10.0 +/- 0.1 with Straightness Tolerance
of 0.05 under Maximum material condition ( MMC )
straightness controlled at 0.05 if cylinder OD measured at
10.1 ( MMC ). Extract bonus can be applied if the cylinder
produced to a smaller diameter size.
Diameter 9.9 for instance, the allowable straightness can
be (10.1-9.9 )+0.05 = 0.25