What Notch Wear Looks Like

Most flank wear spreads fairly evenly along the cutting edge. Notch wear (often labeled Vg on a wear chart) doesn't — it forms as a concentrated groove on the flank and rake faces at the depth-of-cut (DOC) line, the exact boundary where the engaged cutting edge exits the workpiece into free air. That boundary sees a very different thermal, mechanical, and chemical environment than the section of edge buried in the cut, and the edge wears fastest right where those two zones meet.

What Causes It

• A work-hardened layer from the previous pass. Austenitic stainless steels and nickel- or cobalt-based superalloys work-harden aggressively wherever a tool has already passed. That hardened skin sits right at the DOC line on the next pass and concentrates abrasive and mechanical wear there.
• Oxidation and chemical wear at the air-material interface. The exposed edge of the cut is exposed to atmosphere while the buried section isn't, and that difference drives localized chemical attack on the tool right at the boundary.
• Abrasive scale or a hardened skin on hot-rolled or cast stock. Mill scale, sand inclusions, and case-hardened casting surfaces are all harder and more abrasive than the base material underneath, and they sit exactly at the depth the edge is riding.

Why It Matters

Notch wear rarely stays a cosmetic groove. As it deepens it weakens the edge locally, and a burr starts forming at the cut that grows along with the notch. Left unaddressed, it progresses into full edge chipping or fracture — often forcing an insert change even though the rest of the cutting edge still has useful life left. In practice, notch wear is a diagnostic: it's telling you the tool is repeatedly wearing the same exact spot.

How to Manage It

The most effective fix is to vary the depth of cut between passes so the DOC line doesn't land on the same point of the edge every time. When that's not possible, reducing cutting speed and stepping up to a stronger, more wear-resistant edge geometry or grade slows the notch's growth. On scaled or hardened stock, addressing the surface condition before finish passes — or taking a cleanup pass beneath the hardened skin — removes the root cause rather than just working around it.