Oooh! Sharp Objects! *coughs*
A Drag Knife. Name is fairly descriptive of its purpose. The Spindle drags the knife behind it, cutting through the surface material. The material has to be fairly thin (think X-Acto style blades) in order for this to work properly (having said that, some styles take a utility/boxcutter blade)
Thicker material you say? Plunge serrations needed? Enter the Tangential Knife.
Instead of freely rotating, a much stouter knife blade is held by a stepper motor, which is motion controlled to drag the blade through heavier materials.
WidgetWorks Drag Knife (for Vinyl)
Tormach’s Spring Loaded CNC Drag Knife (Carbide Blade, made by WidgetWorks 🙂 )
Rockcliff Machine – Drag Knife (three carbide blades, each of differing angle)