Grinding wheels: Which letter range denotes hard grade wheels in the standard grade scale?

Introduction / Context:
Grinding wheel grade indicates the bond’s holding power on the abrasive grains. It is different from hardness of the abrasive itself. Selecting an appropriate grade prevents glazing, burn, and poor stock removal.

Given Data / Assumptions:

• Standard grade lettering from A (very soft) to Z (very hard).
• Application covers general purpose vitrified or resinoid wheels.
• We are identifying the range representing hard grades.

Concept / Approach:
Soft grades (A–H) release dulled grains readily, good for hard materials. Medium grades (I–P) serve balanced conditions. Hard grades (Q–Z) retain grains longer, suited to soft, ductile materials where self-sharpening is less needed and chip loads are lower per grain.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturers’ catalogs and handbooks confirm these typical groupings, though exact boundaries can vary slightly by supplier.

Why Other Options Are Wrong:

• A to H: soft grades.
• I to P: medium grades.
• A to P: mixes soft and medium; not the hard range.

Common Pitfalls:
Confusing “grade” with “grit size” or “abrasive hardness.” Grade is about bond retention, not grain size or material hardness.

Final Answer:
Q to Z