| Datum
References in the Second Segment Control
Orientation.
When using composite tolerancing,
the second segment tightens the location between features in
the pattern. If datum references are repeated in the second
(lower) segment, the orientation of the pattern is tightened
to the value specified in that segment. In the assembly shown
below, if you want the mounting holes to line up but are not
concerned about the rotation of the parts relative to one
another (as illustrated by the arrow), the datum references
would not be repeated in the lower segment. This is
illustrated on the drawing shown.
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To limit this
rotation, the datum references should be repeated in the
lower segment as illustrated on the drawing below. It is
important to note that even though rotation between the
parts has been limited to 0.3mm, the parts may still
move 0.8mm relative to each other. Next months tip will
illustrate how to restrict movement in one direction
only. |
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