A spoilboard cutter (also called a surfacing bit or spoilboard surfacing bit) is a wide-diameter, flat-bottomed router bit used to machine the top of a CNC spoilboard flat and level. Its whole job is to resurface the sacrificial board your workpieces sit on. First, what’s a spoilboard? It’s the replaceable sheet of MDF (or similar) fastened to a CNC router’s table. Workpieces are clamped or held down on top of it, and the bit is allowed to cut slightly into it during through-cuts. Over time it gets scarred with grooves, holes, and uneven spots. What the cutter does: It takes a very shallow pass across the entire board, shaving off a thin layer so the surface becomes flat and parallel to the machine’s travel. That gives you a consistent Z-zero reference and a good holding surface for vacuum or clamps.

Canadian Woodworker stocks and sells spoilerboard cutters in various sizes from CMT, as well as the replacement carbide insert blades.