Concentration is the amount of diamond held in a given volume of bond, and 100 concentration is defined as 4.4 carats per cubic centimetre, or 72 carats per cubic inch. Higher is not better. It is a trade between shape retention, chip clearance and cost, and the right number depends on the process far more than on the price of diamond.
What The Number Actually Means
Concentration is written against a fixed reference. 100 concentration means 4.4 carats of diamond in one cubic centimetre of working volume. 50 means half of that, 75 means three quarters, 125 means a quarter more than the reference.
Because the reference is fixed, concentration is comparable across suppliers and across bond types. That is the useful part. The unhelpful part is that the same number behaves differently in a resin wheel than in a sintered segment, because the bond around it behaves differently.
Why Lower Concentration Is Often Better
At lower concentration each diamond particle carries more load. That sounds bad, and in a hard, high-pressure operation it is bad. But in a free-cutting operation it is exactly what you want: the particle sits proud of the bond, the chip has somewhere to go, and the wheel stays open.
Low concentration also matters on thin sections and on parts that burn easily. Fewer particles in contact means less heat per unit area at the same feed. On a thin-walled component, that difference is the gap between a good part and a scrapped one.
Why Higher Concentration Is Sometimes The Only Answer
Shape retention is the main reason. A form wheel that has to hold an edge profile, a saw segment that has to keep cutting to the end of its life, a honing stick that must not go out of round: these need enough particles per unit volume that as one dulls, the next is already in position.
The second reason is load. High-pressure, high-feed operations break particles. If the concentration is too low there is nothing behind the broken particle, and the bond starts doing the cutting. That is the point where a wheel stops cutting and starts rubbing.
Typical Starting Points
Resin bond wheels for carbide and tool steel generally run between 75 and 100. Metal bond saw segments for stone and concrete usually run higher, because the segment has to survive impact loading. Electroplated tools are a different case entirely: there is a single layer of grit, so “concentration” is expressed as coverage, and the bond is the plating.
Diamond wire and thin cut-off work sit at the low end of the range for diamond content in the working layer, because the wire has to stay flexible and the slurry has to clear quickly.
Fine grit usually runs at higher concentration than coarse grit for the same job. Smaller particles mean more of them per carat, and the bond has to hold them densely enough to present a continuous cutting surface.
The Cost Argument, Reversed
It is tempting to read concentration as a cost dial: lower concentration, less diamond, lower price. On paper the arithmetic works. In a real process it often fails, because a wheel that wears out of shape in half the time costs more in dressing, downtime and scrap than the diamond saved.
The honest way to compare two concentrations is cost per finished part, not price per wheel. Most buyers who switch to a lower concentration and then switch back do so because their own scrap rate moved, not because the wheel price was wrong.
What Decides The Number
Four inputs are enough to make a first recommendation: the process (grinding, sawing, honing, polishing), the workpiece and its hardness, the bond system, and whether shape retention or surface finish is the limiting requirement. If two of those point in opposite directions, the process usually wins, because the machine and the part are harder to change than the wheel.
Ask the supplier to state the concentration basis along with the grade. A concentration number without a stated reference volume is not a specification, it is an opinion.
Next Step
For bonded tools, start from MBD high-strength grit where shape retention matters, and HDG micron powder for finer resin bond work. Coated grades for high-load bonds are covered in nickel-coated diamond.
Application detail by process: resin and vitrified bond wheels, saw blades and core drills, CMP pad conditioners.