Diamond Lapping Paste

Diamond lapping paste is diamond micron powder held in a carrier and thickened so it stays on the lap instead of running off. The powder in the jar is our own, from the same classification line as our loose micron grades — the grade printed on the label is the grade in the paste, not a repackaged purchase.

Monocrystalline or polycrystalline. Monocrystalline paste is built on blocky single crystals with sharp edges: it cuts quickly and leaves a defined, even scratch pattern, which is what you want on mould steel, carbide and hard coatings before the finishing step. Polycrystalline paste is built on particles that micro-fracture in use, exposing fresh edges instead of dulling, so the finish is finer and more uniform at a lower removal rate. Mirror work on sapphire, SiC, ceramics and gemstone usually goes better on poly; rough lapping and die work on mono.

Three carriers, and the choice matters. Water-based paste rinses off with water, keeps the workpiece cool and leaves no oil film — the default for glass, ceramics, silicon and work that has to be cleaned before inspection. Oil-based paste lubricates better and does not evaporate, so it stays workable through a long lapping cycle and protects steel parts from flash rust. Water-oil dual-use paste can be thinned and cleaned with either, which is what most job shops keep on the shelf when they run mixed materials through the same bench.

Grades from W0.5 to W50. W0.5 to W3 is final polish, with no scratch visible under a bright light. W4.5 to W9 is precision lapping ahead of polish. W13 to W25 is general lapping where you still want a controlled finish. W35 and W50 remove material and hold a dimension rather than refine a surface. W0.25 is available on request for the finest work.

Packing follows use. The 5 g and 10 g syringe (13 mm across, 150 mm long) lays a metered bead straight on the lap, with nothing wasted and nothing drying in an open jar. Jars at 300 g and 1 kg suit a line running the same grade every day. Bulk containers are quoted per order. Concentration, colour coding and label text are set per shipment.

Where paste beats loose powder. Loose micron powder has to be mixed, wetted and kept in suspension on the lap, and on a hand lap or a small machine that is a variable every operator introduces differently. Paste removes it — the concentration is already set, the carrier is already matched, and the only decision left is how much to lay down. For a shop running twenty different parts a week, that repeatability is worth more than the small difference in cost per carat.

What goes wrong, and why. Three failures cover most of the complaints we hear. Paste used too coarse for the required finish — stepping from W13 straight to a mirror specification never works, because the scratches are cut too deep to polish out afterwards. Carrier chosen against the cleaning step — oil-based paste on parts that go straight into an aqueous washer leaves a film that shows up later as haze under inspection. And paste allowed to dry on the lap — once the carrier is gone the powder clumps and cuts a gouge instead of a scratch. Keep the lap charged, keep the syringe capped, and none of the three happen.