Diamond grit numbers follow the GB/T 2481 series: the number after W gives the particle size range, so a lower number means a finer grain. The common mistake is to jump straight to the finest grade for surface quality — efficiency collapses, cost doubles, and the surface can end up worse because grains release too early and cut unevenly.
Four stages, four bands
- Roughing / stock removal: W28 – W40. Takes the bulk of the material; removal rate matters more than surface.
- Semi-finishing: W14 – W20. Corrects the surface left by roughing and leaves an even stock for finishing.
- Fine grinding: W7 – W10. Controls dimensional accuracy and roughness; this stage decides the final form.
- Super-finishing / polishing: W0.5 – W3.5. Surface quality is the objective, removal is minimal.
Three parameters beyond grit
1. Bond
Resin bonds self-sharpen and are slightly elastic, which suits finishing and polishing. Bronze bonds hold the grain firmly and keep form, which suits roughing and high-load stations. The same W14 behaves very differently in the two.
2. Concentration
Concentration is the diamond content in the working layer. High concentration gives life but raises cutting resistance; low concentration cuts freely but wears quickly. Roughing usually runs higher concentration for life, finishing lower for surface quality.
3. Machine and pressure
The optimum grit on a high-speed fine grinding machine is not the optimum for hand lapping. With high speed and pressure you can go one grade coarser without losing surface quality; at low pressure by hand you need a finer grade to polish out.
Micron powder spans a wider range
Diamond micron powder for grinding and polishing covers W0.5 to W100 — the coarse end removes stock quickly, the fine end produces a mirror. What matters is not how fine a grade you can buy but how tight the distribution is: a wide distribution with a few coarse particles will scratch a polished surface no matter what the label says.