How things work visualizations use a variety of visual techniques to

depict the operation of complex mechanical assemblies.We present

an automated approach for generating such visualizations. Starting

with a 3D CAD model of an assembly, we first infer the motions of

individual parts and the interactions between parts based on their

geometry and a few user specified constraints. We then use this

information to generate visualizations that incorporate motion arrows,

frame sequences and animation to convey the causal chain

of motions and mechanical interactions between parts. We present

results for a wide variety of assemblies.