Hole bends or leans (poor straightness)

?Likely causes

• Mounting runout is largeAgreed by 2+ makers^[1][2][3][4]
• Lip height is large or the point is asymmetricAgreed by 2+ makers^[2][4]
• Pilot hole (guide hole) is inaccurate or shallowAgreed by 2+ makers^[2][5][3][4]
• Workpiece surface is tilted or not perpendicularOne maker^[1][4]
• Insufficient drill rigidityAgreed by 2+ makers^[4][3]
• Chip clogging or unsuitable feedOne maker^[1]

✓Fixes

Cutting conditions

• Increase the feed to break chips and reduce the step amount to prevent cloggingOne maker^[1]

Tool

• Regrind with equal lip heightsAgreed by 2+ makers^[2][4]
• Use a high-rigidity drill (large web thickness, short flute length)Agreed by 2+ makers^[4][3]

Setup

• Reduce mounting runoutAgreed by 2+ makers^[1][2][3][4]
• For deep holes, drill a pilot hole (L/D 1-3) with a short drill first, then use a long drillAgreed by 2+ makers^[5][6][4]
• If the surface is tilted, center drill or machine a flat seat before drillingOne maker^[1][4]

Where sources differ: Using a pilot hole reduces hole runout by 70-80% compared with not using one (Mitsubishi e-learning).

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