Grit Calculator
Select material, process and target roughness – you get an initial orientation for the right diamond or CBN grit size.
View data basis, estimation method and limitations
Where the values come from
The calculator works in three stages. First: if a documented value exists for the material, grit and process, only that value is used – shown in the result as manufacturer data or EHWA validated. Second: if a grit is missing within a documented material group, we scale linearly by mean grain size from the nearest documented point. Third: if a material group has no documented values at all, we transfer the ladder of a related group using a reasoned factor. Stages two and three are engineering estimates and are always labelled as such in the result. A process factor applies on top; the value for creep feed and flute grinding comes from our own documented case.
Documented values: diamond on cemented carbide
| Grit | Grain size approx. | Ra range | Basis |
|---|---|---|---|
| D181 | 167 µm | 0.4–0.7 µm | Manufacturer data |
| D126 | 118 µm | 0.4–0.5 µm | Manufacturer data |
| D91 | 83 µm | 0.3–0.4 µm | Manufacturer data |
| D64 | 63 µm | 0.2–0.3 µm | Manufacturer data |
| D46 | 47 µm | 0.1–0.2 µm | Manufacturer data |
| D76 | 72 µm | 0.4–0.6 µm | EHWA validated |
Documented values: CBN on hardened steel
| Grit | Grain size approx. | Process | Ra range |
|---|---|---|---|
| B181 | 167 µm | Plunge grinding | 1–1.1 µm |
| B181 | 167 µm | Oscillating / traverse grinding | 0.9–1.1 µm |
| B151 | 140 µm | Plunge grinding | 0.9–1 µm |
| B151 | 140 µm | Oscillating / traverse grinding | 0.8–0.9 µm |
| B126 | 118 µm | Plunge grinding | 0.8–0.9 µm |
| B126 | 118 µm | Oscillating / traverse grinding | 0.6–0.8 µm |
| B107 | 99 µm | Plunge grinding | 0.6–0.8 µm |
| B107 | 99 µm | Oscillating / traverse grinding | 0.5–0.6 µm |
| B91 | 83 µm | Plunge grinding | 0.5–0.6 µm |
| B91 | 83 µm | Oscillating / traverse grinding | 0.4–0.5 µm |
Only these values are documented. Everything else is derived from them and labelled as an engineering estimate.
What this calculator does not do
The output is an initial orientation, not a guaranteed Ra value. Bond, machine, dressing condition, coolant and process parameters shift the result. End mills, indexable inserts and PCD/PCBN cutting materials are not covered here – their internal grain size is not a FEPA wheel grit; grinding such tools, however, is covered.
Roughness parameters per DIN EN ISO 21920, areal parameters per DIN EN ISO 25178, grit sizes per DIN ISO 6106 (FEPA). Values must be verified under the corresponding measuring conditions.