Grinding wheel structure: A dense (closely spaced grain) wheel is most appropriately used for which application?

Introduction / Context:
Besides grit size and bond grade, wheel structure (spacing between abrasive grains) affects chip accommodation and heat generation. Dense structures have more grains per unit volume with smaller chip spaces; open structures have fewer grains and larger pores. Correct structure selection prevents loading and controls finish.

Given Data / Assumptions:

• Conventional vitrified or resinoid bonded wheels.
• Need to distinguish roughing vs finishing performance.
• Materials may range from soft ductile to hard/brittle substrates.

Concept / Approach:
Dense wheels place many cutting points in contact, distributing load and generating a fine finish at shallow chip thickness. They suit finishing operations and tight tolerances. For roughing soft or gummy materials, an open structure is preferred to provide chip clearance and reduce wheel loading. While dense wheels can be used on hard/brittle materials when finishing, stating “all of these” is overly broad; the most defensible single best answer is “finishing cuts requiring fine surface.”

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer selection guides associate dense structures (and finer grits) with finishing passes and dimensional grinding; open structures are recommended for heavy stock removal and soft, ductile materials.

Why Other Options Are Wrong:

• Hard materials: often finished with dense wheels, but for roughing hard materials, chip clearance may still be needed.
• Brittle materials: may also finish well with dense wheels, yet as a general rule the single most precise answer is the finishing application.
• All of these: too inclusive and not universally valid.
• Roughing soft, gummy materials: requires open structure to avoid loading.

Common Pitfalls:
Assuming “denser is always better.” Dense wheels can overheat work surfaces and load rapidly when asked to remove heavy stock on ductile materials.

Final Answer:
finishing cuts requiring fine surface