Comparative process speeds: With equally rigid machines and identical tool–work materials, which operation is normally run at the lowest cutting velocity?

Introduction / Context:
Cutting velocity limits are set by tool material, heat dissipation, tool geometry, and system rigidity. Among common processes, practical speeds differ even for the same material because of tool overhang, engagement style, and stability.

Given Data / Assumptions:

• Machines are equally rigid overall (but tool setups differ).
• Same tool–work material pairing across processes.
• Typical production conditions (no special coatings or ceramics).

Concept / Approach:
Grinding generally uses the highest surface speeds due to abrasive hot hardness. Milling also permits relatively high speeds with intermittent cutting and efficient chip evacuation. Turning speeds are moderate and can be high with carbide. Boring uses a long, slender bar (overhang), reducing dynamic stiffness and increasing chatter risk; thus, boring commonly runs at lower speeds than an equivalent external turning job to maintain stability and surface finish.

Step-by-Step Solution:

Verification / Alternative check:
Shop guidelines often specify speed reductions (and feed adjustments) for internal turning/boring versus external turning on the same work material and insert.

Why Other Options Are Wrong:

• Grinding: typically the highest surface speeds (tens of m/s).
• Milling: intermittent cutting permits relatively high permissible speeds.
• Turning: external turning allows higher speeds than boring for the same tool system.

Common Pitfalls:
Equating machine nameplate rigidity with setup rigidity; boring bar dynamics often govern allowable speed regardless of base machine stiffness.

Final Answer:
Boring