Grinding Wheel Selection Guide: Grain, Bond, Grade and Grit Explained
Published 15 May 2025 · Drishti Powertech LLP
Every grinding wheel is defined by five key parameters: abrasive grain type, grain size (grit), grade (hardness), structure (spacing), and bond type. Getting these wrong results in either rapid wheel wear (uneconomical), burning or glazing the workpiece surface, or — in the worst case — a wheel fracture. This guide demystifies the wheel marking system and helps you select the right specification the first time.
Abrasive Grain Types
The four main abrasive grains: (1) Aluminium oxide (A) — the most versatile, used for steel, stainless steel, cast iron, and general-purpose grinding. (2) Silicon carbide (C) — harder and sharper than Al2O3, ideal for non-ferrous metals (aluminium, brass), cast iron, ceramics, and stone. (3) Ceramic aluminium oxide (Tyrolit's Cerabond X) — self-sharpening micro-fracturing grain that stays sharp longer, runs cooler, and removes more material per unit of wheel wear than conventional aluminium oxide. Best for stainless steel and high-alloy steels. (4) CBN (cubic boron nitride) and diamond — superabrasives for hardened steels, carbide, ceramics, and precision grinding. Very long life but high initial cost.
Grit Size (Grain Size Number)
The grit number indicates the sieve size used to grade the abrasive particles — the higher the number, the finer the grain. Coarse grit (16–30): fast stock removal, rough surface finish, used for rough grinding and heavy material removal. Medium grit (36–60): general-purpose grinding balancing stock removal and surface finish. Fine grit (80–120): finishing passes, smoother surface. Very fine (150–220): superfinishing. For most manual angle grinding and cut-off work, grit 24–36 is standard.
Grade (Hardness)
Wheel hardness refers to the strength of the bond holding abrasive grains — not the hardness of the abrasive itself. A harder-grade wheel retains grains longer (slower wear); a softer-grade wheel releases worn grains faster, exposing fresh cutting surfaces (self-sharpening). The key rule: use a softer wheel on hard materials (hardened steel, carbide), and a harder wheel on soft materials (aluminium, mild steel). A wheel that glazes (polishes without cutting) is too hard; a wheel that wears away rapidly is too soft.
Bond Types
Vitrified bond (V): ceramic glass bond — the most common for precision grinding. High strength, rigid, porous (good coolant access), and thermally stable. Resinoid bond (B): synthetic resin — flexible, absorbs vibration, used for cut-off wheels and rough grinding. Rubber bond (R): used for high-finish centreless grinding regulating wheels. Metal bond (M): used for diamond and CBN wheels, highest precision grinding. Electroplated bond: single layer of abrasive bonded by electroplated nickel — maximum material removal rate, lowest profile accuracy retention.
Reading the Full Wheel Marking
Example marking: A 46 K 5 V. A = aluminium oxide grain. 46 = medium grit. K = medium-hard grade (A=softest, Z=hardest; mid-range is J–N). 5 = medium-dense structure (1=densest, 15=most open). V = vitrified bond. For a standard steel-grinding wheel on an angle grinder, a specification of A 36 R BF (aluminium oxide, 36 grit, soft grade, resinoid bond, fibreglass reinforced) is typical. Tyrolit's product range includes wheel specifications optimised for every material and application — from stainless steel to titanium to concrete.
Conclusion
Matching the grinding wheel specification to your workpiece material, machine power, and required finish is essential for safety, productivity, and economy. Never use a wheel rated for a lower peripheral speed than your grinder's maximum RPM. As an authorised Tyrolit distributor, Drishti Powertech supplies the full Tyrolit catalogue and provides free application support to help you select the optimal specification for your workshop or production line.
Frequently Asked Questions
Why does my grinding wheel burn the workpiece?
Burning (discolouration of the workpiece surface) indicates the wheel is cutting inefficiently — too hard a grade for the material, wrong grain type, excessive feed rate, or insufficient coolant. Try a softer grade wheel, ensure the wheel is dressed correctly, reduce feed pressure, and apply coolant if applicable.
How do I safely store and handle grinding wheels?
Store wheels vertically in a dry environment away from vibration. Never drop a wheel — even invisible cracks will cause fracture at speed. Always perform a ring test (tap gently with a mallet — a clear ring indicates no cracks; a dull thud indicates damage) before mounting. Mount correctly using flanges of equal diameter with blotting paper gaskets.
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