Grinding wheel selection for high stock removal: For fast removal of material during grinding operations (heavy roughing), which grain size specification should be preferred?

Introduction / Context:
Choosing the proper grinding wheel is critical for productivity and surface integrity. One of the most important parameters is grit size (grain size). When the objective is fast stock removal — for example, rough grinding to quickly reduce dimensions — the grit size and wheel structure must allow large chips to form and escape without loading or glazing.

Given Data / Assumptions:

• Abrasive machining of steels or common shop alloys.
• Goal is high material removal rate (MRR), not surface finish.
• Conventional bonded abrasives (aluminium oxide or silicon carbide).

Concept / Approach:
Coarse grits have larger cutting points that penetrate deeper, forming thicker chips and enabling higher MRR. They also create larger chip spaces, reducing wheel loading. Fine grits, by contrast, produce many small cutting edges, ideal for fine finishes but limited in chip thickness and MRR. Medium grits compromise between the two. Wheel structure (open vs dense) further modulates chip clearance, but the primary lever for stock removal is coarse grit size.

Step-by-Step Solution:

Verification / Alternative check:
Shop practice recommends coarse, open-structure wheels with soft-to-medium grade for aggressive roughing; trial cuts will show lower power spikes and less glazing compared to fine grit wheels for the same feed and depth of cut.

Why Other Options Are Wrong:

• Fine grained: optimized for finish, not for heavy MRR.
• Medium grained: balanced choice, still not optimal for maximum MRR.
• Micro-grained superfinish: designed for very fine finishes at minimal stock removal.
• Closed structure with small grit: tends to load up under heavy chip volume.

Common Pitfalls:
Confusing wheel grade (bond hardness) with grit size; both matter, but grit size primarily controls chip thickness for a given condition. Also, forgetting to ensure adequate coolant and wheel dressing for sustained roughing performance.

Final Answer:
coarse grained