Hole becomes oversized (reaming)

?Likely causes

• Reamer diameter is largeAgreed by 2+ makers^[1][2]
• Cutting speed or feed is highAgreed by 2+ makers^[1][2]
• Runout of the spindle or the reamer (lead chamfer)Agreed by 2+ makers^[1][2][3]
• Built-up edge, or welding on the marginAgreed by 2+ makers^[1][2]
• Misalignment between the pilot hole and the reamerAgreed by 2+ makers^[1][2]
• Poor lead chamfer geometry (short, inconsistent, or large lead angle)Agreed by 2+ makers^[1][3]
• Reaming allowance is largeOne maker^[2]
• Burnishing action is insufficient (narrow margin, large back taper)Agreed by 2+ makers^[2][3]
• Coolant oil content is too highOne maker^[1]

✓Fixes

Cutting conditions

• Reduce the rotation speedAgreed by 2+ makers^[2][1]

Tool

• Switch to a smaller-diameter reamerOne maker^[2]
• Use a reamer with a wider margin and a smaller back taperAgreed by 2+ makers^[2][3]

Setup

• Eliminate reamer runout (mounting accuracy, spindle runout, alignment)Agreed by 2+ makers^[2][3][1]
• Increase the pilot hole diameter to reduce the reaming allowanceOne maker^[2]
• Eliminate misalignment between the pilot hole and the reamerAgreed by 2+ makers^[2][1]

Where sources differ: The Sandvik reamer reference lists only causes and gives no countermeasures.

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