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Use the new free state symbol for
your plastic, sheet metal and other flexible parts. In section
1.4 FUNDAMENTAL RULES of Y14.5, paragraph (l) tells us that
"All dimensions and tolerances apply in a free state
condition. This principle does not apply to nonrigid parts as
defined in paras. 2.7.1.3(b) and 6.8." The default, then, is
that all parts are considered rigid unless there is some
indication that the part may be flexed or distorted for
inspection. A way to indicate that a part is not rigid is to
add a constraint note. If some tolerances are to be checked
with the part not constrained, the new free state symbol may
be added to specific tolerances. Many useable sheet metal and
plastic parts will pass inspection and be functional if
clamped to a condition that simulates the assembled or
functional state. Usually when a constraint note is applied
to a drawing, at least one tolerance should be inspected in
the free state to limit the free state variation. In this
example the entire part is inspected with the part constrained
except for the flatness spec which would be checked
unrestrained in the free state.
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