The hardness of a grinding wheel is determined by the

A grinding wheel is made up of tiny cutting points called abrasive grains. These grains are held together by a bonding material — think of it like glue. Now, when we talk about the “hardness” of a grinding wheel, we’re not talking about how hard those grains are, but rather about how tightly the bond holds onto them.

Option A: Hardness of abrasive grains – This is about the toughness of each tiny grain. Yes, it matters for cutting performance, but it’s not what defines the wheel’s hardness.

Option B: Ability of the bond to retain abrasives – This is the real meaning of hardness here. A hard wheel has a strong bond that holds the grains for a long time, even when they get worn. A soft wheel’s bond lets go of the grains more easily, constantly exposing fresh cutting points.

Option C: Hardness of the bond – The bond might be physically hard, but if it can’t hold the grains well, the wheel won’t be considered “hard.” It’s the holding strength that matters.

Option D: Ability to penetrate the work piece – That’s about cutting action, not hardness. In fact, a softer wheel might cut faster because it exposes new grains more often.

In short: If the wheel holds onto its abrasive grains stubbornly, it’s “hard.” If it lets them go quickly, it’s “soft.” That holding power — the ability of the bond to retain abrasives — is what truly defines grinding wheel hardness.