🔍 Use an **up-cut spiral bit** for operations like deep slots, mortises, or profiles where chip evacuation is critical and the bottom face needs a smooth finish (for example, CNC cutting through a piece so the bottom exit edge is clean):contentReference[oaicite:3]{index=3}. Conversely, choose a **down-cut bit** for grooves or pockets where the top surface appearance matters – the down-cut shearing action will prevent splintering of the top veneer or fibers:contentReference[oaicite:4]{index=4}. In summary, up-cuts are best for clearing chips and protecting the bottom edge, while down-cuts are best for protecting the top edge. Many woodworkers keep both types on hand and switch depending on which face of the material needs the cleanest cut.

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