The usual question is “how much is your W14 pellet”. But W14 is only a grit size. What actually decides whether a pellet works is the combination of bond hardness and diamond concentration — and that has to follow the glass.
K9 / BK7: the generalist, judged on consistency
K9 is the most common optical glass: moderate hardness, chemically stable, not difficult to grind. The goal here is a stable removal rate. On a running line, if pellet-to-pellet cutting force varies, thickness tolerances drift. A standard resin formulation is right; the requirement is batch consistency, not a special recipe.
ZF flint: soft, lead-bearing, scratch sensitive
ZF heavy flint is soft and contains lead, and tends to scratch and orange-peel. The cause is rarely the grit size but excessive stress at each cutting point. Soften the bond so dull grains release, and lower the concentration slightly to spread the load across more grains. Going finer usually just loads the pellet and raises grinding heat.
Borosilicate: brittle, chip sensitive
Borosilicate glass for automotive lighting has low thermal expansion and marked brittleness, so edges chip easily. Beyond the formulation, pellet layout and tooling matter: on a curved part, a layout that does not follow the surface concentrates pressure and chips the edge. That is why lamp parts are supplied as plated sets, not loose pellets.
Sapphire: hard and brittle at the same time
Sapphire is second only to diamond in hardness, so removal is slow; but it is also brittle, so chipping risk is high. The usual answer is two stages: bronze-bond pellets to take the stock, resin-bond pellets to control the surface, with a moderate concentration in the finishing stage. One grade from start to finish gives either poor efficiency or a high reject rate.
What to tell us when enquiring
- The glass type (K9, ZF7, borosilicate, sapphire) — “optical glass” is not enough
- Part size and curvature, which determine pellet diameter and layout
- Current cycle time and defect mode (chipping, scratching, thickness drift)
- Machine model and plate interface
With those four, selection is usually right first time.