Wire EDM and sinker EDM leave behind a recast layer — the thin, hard 'white layer' of resolidified material on the machined surface — along with a heat-affected zone that has to be removed before the cavity can be polished to production finish. That removal is the job of EDM polishing stones, which are formulated specifically for this task rather than for general deburring.
Grades: AM-8, AS-9, and orange
EDM polishing stones are sold in grades that define the abrasive type, bond hardness, and cutting behavior. In the DMS range:
- AM-8 (catalog e.g. 20120) — a general EDM finishing stone for the standard coarse-to-fine progression after the recast layer is broken through.
- AS-9 (catalog e.g. 21260) — a finer, harder grade for intermediate and final finishing, producing a smoother surface with less stone breakdown.
- Orange (catalog e.g. 82005) — a dedicated EDM stone grade for cleaning recast and bringing the surface to a consistent scratch pattern before diamond paste.
Within each grade, the stone is selected by grit: coarser grits cut the recast layer aggressively but leave a deeper scratch pattern; finer grits refine the surface but do not remove material quickly. The standard practice is a progression — coarse to remove the white layer, then medium, then fine — before switching to diamond compound for the final polish.
Size, shape, and holders
Stones are stocked in a range of sizes and cross-sections to match the cavity geometry: larger blocks for open areas, thin slivers for ribs and detail. For tight corners and small details, stones are mounted in holders — including ceramic and polishing stone holders — that give the toolmaker a stable grip without flexing, which keeps the stone flat against the surface.
Practical notes
- Always work coarse-to-fine; jumping straight to a fine stone on heavy recast loads it and cuts slowly.
- Keep the stone moving and light — heavy pressure breaks the bond and gouges the surface.
- For deep ribs and small details, use a thin stone in a holder instead of a hand-held block.
- Finish with the finest stone grade before moving to diamond compound so the scratch pattern is uniform.
If you are not sure what grade to start with, tell us the surface condition (heavy recast after roughing EDM, or a light cleanup pass) and the cavity geometry, and we will recommend the stone sizes, grades, and grit progression.
Catalog item plug: Tooling Components stocks DMS EDM polishing stones in AM-8, AS-9, and orange grades, in multiple sizes and grits, plus ceramic and polishing stone holders.