Hole finishing around a fastener seat The machining operation used to smooth and square the surface immediately surrounding an existing hole (to seat a bolt head or washer) is called:

Introduction / Context:
Many assemblies require a flat, smooth bearing surface around a hole so that bolt heads, nuts, or washers sit properly and distribute load. A dedicated finishing operation is used for this purpose.

Given Data / Assumptions:

• An existing through or blind hole already drilled.
• Need for a flat circular land normal to the hole axis.

Concept / Approach:
Spot facing uses a spot facer (often piloted) to machine a shallow, flat seat around the hole. It corrects surface non-flatness, removes scale, and ensures consistent seating. This differs from counterboring (which enlarges the hole to a larger cylindrical section) and countersinking (which makes a conical entry).

Step-by-Step Solution:
Identify required geometry: a flat circular seat, not a deeper cylindrical enlargement.Select operation that produces a flat face at right angles to hole axis → spot facing.Use a piloted tool to maintain concentricity and prevent chatter.

Verification / Alternative check:
Engineering drawing notes often specify “SF” or a surface finish symbol adjacent to bolt holes indicating spot facing, not counterboring.

Why Other Options Are Wrong:

• Counter-sinking (A) produces a conical mouth for flat-head screws.
• Counter-boring (B) makes a larger cylindrical recess to recess a bolt head, not simply square the surrounding surface.
• Trepanning (C) cuts large circular holes or disks; not a seat finish.
• Reaming (E) improves hole size/finish internally; not the surrounding face.

Common Pitfalls:
Using counterbore when only a shallow seat is needed; neglecting pilot guidance causing off-axis faces.

Final Answer:
spot facing