Burrs at the hole exit (breakthrough)

?Likely causes

• Feed is large at breakthroughAgreed by 2+ makers^{[1][2][3][4][5]}
• Honing is largeOne maker^[1][2]
• Mounting runoutOne maker^[4]
• Cutting edge is damagedOne maker^[3]

✓Fixes

Cutting conditions

• Reduce the feed before breakthrough (to about half, a 20-50% reduction)Agreed by 2+ makers^{[1][2][3][4][5]}

Tool

• Reduce the honingOne maker^[1][2]
• Add a chamfer or radius to the drill shoulder, or increase the clearance angleOne maker^[4][5]
• For shallow holes (2D or less, or 3D or less with through-coolant), use a flat drillOne maker^[4][5]

Setup

• Reduce mounting runout and supply cutting fluid wellOne maker^[4]
• Remove burrs that have formed with a back-deburring toolOne maker^[4][5]

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