  Tolerancing of assembly mechanisms is a major interest in the product life
cycle. One can distinguish several models with growing complexity, from
1-dimensional (1D) to 3-dimensional (3D) (including form deviations), and two
main tolerancing assumptions, the worst case and the statistical hypothesis.
This paper presents an approach to 3D statistical tolerancing using a new
acceptance criterion. Our approach is based on the 1D inertial acceptance
criterion that is extended to 3D and form acceptance. The modal
characterisation is used to describe the form deviation of a geometry as the
combination of elementary deviations (location, orientation and form). The
proposed 3D statistical tolerancing is applied on a simple mechanism with lever
arm. It is also compared to the traditional worst-case tolerancing using a
tolerance zone.
