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 Smooth
the Surface with Profile on a Unit Basis
(in accordance with the ASME
Y14.5-2009 standard)
PDF of This Tip
 Past
standards have shown straightness and flatness
applications "on a unit basis". The purpose of
applying a profile tolerance on a unit basis is to
avoid abrupt changes in the surface. This revision
of the Standard states that profile of a surface may
be applied on a unit basis similar to straightness
or flatness. [8.3.2.1]
 The
location of the top surface of this part is
controlled by the 0.6 profile of a surface tolerance
relative to the datum established by datum feature
A. If this was the only tolerance applied to this
surface, there could be steps in the surface as
large as 0.6. The 0.1/Ř10 profile tolerance has been
applied to avoid these abrupt steps in the surface.
This tolerance means that any area within a diameter
of 10 mm on the top surface must meet the profile
tolerance of 0.1.
Think of this tolerance zone as a coin with a
diameter of 10 mm that is 0.1 mm thick. In this
limited area the profile tolerance is the same as a
flatness tolerance. The surface within this limited
area must fit “inside” the coin. Now imagine that
you can push the coin (tolerance zone) around on the
surface. No matter where the coin is on the surface,
that Ř10 area must be flat within 0.1.
Even though this is being shown on a flat surface,
it can be applied to contours as well but you would
need to imagine a flexible coin that could conform
to the basic contour to visualize the tolerance
zone.
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