Boring tool height effect: Setting an internal boring tool above the spindle centerline primarily causes which change in effective angles?

Introduction / Context:
Tool setting height relative to the work centerline changes the geometry seen at the cutting edge. In boring (an internal turning operation), improper height can alter effective rake and clearance, influencing cutting forces, chip flow, and surface finish.

Given Data / Assumptions:

• Internal boring with a single-point tool at nominal geometry.
• Small offsets relative to center height.
• Conventional right-hand tool and standard spindle rotation.

Concept / Approach:
Moving the tool above the centerline rotates the effective cutting wedge relative to the work. Geometrically, this tends to increase the effective rake angle (tool appears “sharper”), while reducing the effective clearance angle (greater risk of rubbing if excessive). The converse occurs if the tool is set below center.

Step-by-Step Solution:

Verification / Alternative check:
Sketching the tool at different heights relative to the bore center confirms the angular changes; shop practice warns about rubbing when boring tools are set too high.

Why Other Options Are Wrong:
Options showing rake ↓ with tool above center contradict the standard geometric effect.“No significant change” ignores the real geometric sensitivity to height.

Common Pitfalls:
Setting the tool so high that clearance vanishes, causing chatter or poor finish; misreading external vs. internal turning geometry.

Final Answer:

Increase in effective rake angle and decrease in effective clearance angle