Kerf

Kerf is the width of material removed by a cutting process—in CNC routing, laser cutting, plasma, sawing, and similar operations, it is the gap left between the two finished cut edges. In CNC/millwork terms, kerf is the amount the tool path must be compensated so the finished part matches the programmed dimension, with software or controller typically offsetting the tool path by half the kerf for inside versus outside cuts.

On a CNC router, a part programmed at exact nominal size will cut undersized or oversized if tool compensation is not applied, because the cutter removes material on both sides of the centerline. Inside profiles and holes are offset inward by roughly half the kerf; outside profiles are offset outward by roughly half the kerf so the final part lands on spec. In nesting and sheet goods production, kerf affects part spacing and yield, because adjacent parts must be separated enough to account for material removed. In millwork, kerf bending uses a series of cuts to reduce stiffness so plywood or sheet stock can conform to a radius; the width, depth, spacing, and count of kerfs control the bend behavior and finished radius quality. Shops verify kerf with test cuts from the same material and thickness, then adjust offsets in CAM or nesting software rather than assuming a catalog value.

• ⚠️Ignoring tool wear or process drift: A worn router bit, dull saw blade, or changing laser focus alters the actual kerf, so parts that were on size in the morning start fitting loose or tight later in the run.
• ⚠️Using the wrong compensation side: Offsetting an inside pocket like an outside contour makes the tool remove material in the wrong direction, leaving the hole too large or the part too small and causing press-fit failures or loose joinery.
• ⚠️Assuming kerf is constant across materials: Copying a setting from plywood to MDF, acrylic, mild steel, or thicker stock creates systematic dimensional error and nesting collisions, because different sheet goods and thicknesses produce different kerfs.