Notch wear: what it looks like, why it happens, how to fix it
A local notch or deep wear spot exactly at the depth-of-cut line, while the rest of the edge looks almost unworn. At the depth-of-cut line the edge meets the work-hardened layer left by the previous pass, the oxide or casting skin, and the burr at the free surface. That one point carries a load the rest of the edge never sees.
| What you see | Mechanism | First fix | Most affected |
|---|---|---|---|
| A local notch or deep wear spot exactly at the depth-of-cut line, while the rest of the edge looks almost unworn. | At the depth-of-cut line the edge meets the work-hardened layer left by the previous pass, the oxide or casting skin, and the burr at the free surface. | Vary the depth of cut so the notch never sits in one place, and use a smaller entering angle to spread the load. | ISO M (stainless steel), ISO S (superalloys and titanium) |
Why it happens
- Work-hardening materials (austenitic stainless, nickel and cobalt superalloys) leave a hardened skin exactly where the next pass engages.
- Scale, forging skin or casting skin is abrasive and sits at the outer edge of the cut.
- A constant depth of cut puts the same point of the edge into the same hard zone pass after pass.
How to measure and judge it
ISO 3685 treats notch wear as a localised wear form measured separately from the average flank land (VBN). In practice the notch is judged by its depth against the shop limit, because it is the point where the edge will break.
Fixes, in the order to try them
- Change ap between passes (ramping or staggered depths) so the notch position moves.
- Use a smaller entering angle (larger lead) or a round insert to thin the chip at the depth-of-cut line.
- Reduce Vc and choose a tougher grade for M and S materials.
- Remove scale or skin in a separate pass with a robust grade before finishing.
Do not confuse it with
Damage that runs along the whole engaged edge is flank wear or plastic lowering, not a notch. First ask: is it everywhere, or at one point? See tool wear mechanisms.
Other wear modes
Flank wear · Crater wear · Built-up edge (BUE) · Plastic deformation · Thermal cracking · Edge chipping and fracture · All eight failure modes in one table · Mechanisms in depth
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Frequently asked questions
What is notch wear?
Notch wear is localised wear at the depth-of-cut line. It forms there because that is where the edge meets the work-hardened layer, scale or burr at the outer edge of the cut.
How do you prevent notch wear in stainless steel?
Vary the depth of cut between passes, use a smaller entering angle or a round insert, lower the cutting speed and use a tougher grade suited to ISO M.