Boundary wear (groove-like wear at the depth-of-cut line)

?Likely causes

• Work-hardening or sticky materials (stainless steel, heat-resistant alloys)Agreed by 2+ makers^[1][2][3][4]
• Hard surface such as black scale, casting skin, or mill scaleAgreed by 2+ makers^[2][3][5][6]
• The depth-of-cut line is the boundary between the hot zone and air, so it oxidizes easilyOne maker^[3][5][7]
• Edge geometry is too negativeOne maker^[1]

✓Fixes

Cutting conditions

• Change the depth of cut with each pass to shift the position of the boundaryOne maker^[1][2]
• Reduce the cutting speedAgreed by 2+ makers^[2][8]

Tool

• Increase the lead angle (side cutting edge angle) or use a round insertAgreed by 2+ makers^[3][8][2]
• Increase the corner radius and keep the depth of cut at or below the corner radiusOne maker^[3]
• Use a sharp edge geometry with a large rake angleAgreed by 2+ makers^[8][5][1]

▦Notes by material

• Stainless steel: Rubbing on the work-hardened layer tends to cause boundary damage, and it also causes burrs on the machined surface^[4][1]
• Cast iron: The black scale layer is hard and unstable, and most cast iron troubles occur when machining includes black scale^[6]

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