Hole position shifts or hole is not round (rice-ball shape)

?Likely causes

• The chisel edge slips at entry (drill walk)Agreed by 2+ makers^[1][2][3]
• Mounting runout is largeAgreed by 2+ makers^{[4][5][2][6][3]}
• Variation in lip height unbalances the cuttingAgreed by 2+ makers^[5][2][1]
• The center hole angle and the point angle of the main drill do not match, so contact starts at the shoulderOne maker^[7][4]
• Flute length is too longOne maker^[6]
• Workpiece surface is not perpendicularOne maker^[4][2]

✓Fixes

Cutting conditions

• If it wanders at the entrance, reduce the rotation speed and increase the feed to stabilize it with thrustAgreed by 2+ makers^[5][1]
• Reduce the feed at entryOne maker^[6][3]

Tool

• Use a point geometry with good entry, such as X-type thinningAgreed by 2+ makers^[1][6][3][2]

Setup

• Keep mounting runout within 20 μmAgreed by 2+ makers^[5][8]
• Center drill with a point angle equal to or larger than that of the main drill, and keep it separate from chamferingOne maker^[7][4]
• Locate with a bushing or guide holeAgreed by 2+ makers^[1][2]

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