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We describe the design and implementation of a coherent sweep plane slicer, built on top of a topological data structure, which “slices” a tessellated 3-D CAD model into horizontal, 2.5-D layers of uniform thickness for input to layered manufacturing processes. Previous algorithms for slicing a 3-D b-rep into the layers that form the process plan for these machines have treated each slice operation as an individual intersection with a plane, which is needlessly inefficient given the significant coherence between the finely spaced slices. An additional shortcoming of many existing slicers that we address is a lack of robustness when dealing with non-manifold geometry. Our algorithm exploits both geometric and topological inter-slice coherence to output clean slices with explicit nesting of contours.