ForMatter/Finishes/mold_finish/SPI A2 (high mirror polish, #3 diamond)
finish_mold_spi_a2

SPI A2 (high mirror polish, #3 diamond)

mold_finish · mirror · SPI A-2, high optical mold finish, lens mold polish

The mold cavity polished with #3 grade diamond paste — Ra ~0.05 µm. The molded plastic part comes out optically transparent where the mold was clear, mirror-bright where the part is metallic-look. Lens covers, transparent display windows, the inside of a clear water bottle, optical-grade injection-molded parts.

Society of the Plastics Industry (SPI / SPE) finish standard A2 — diamond-paste polish using #3 grade (0–2 µm particle) on a hard tool steel cavity (P20, H13, or hardened S7). Surface roughness Ra 0.025–0.05 µm. A1 is finer (#1 diamond, Ra ~0.025); A3 is coarser (#6 diamond, Ra ~0.1). All A-series are mirror finishes; the mold cost rises sharply with the smaller numbers. A2 is the practical optical-injection-molded standard. Releases molded parts cleanly only with sufficient draft (3°+) and high-flow resin; transparent grades of PMMA / PC / COC reproduce the polish faithfully.

character — optical mirror, glassy, transparent in clear resin, no draft lines visible.

Finish properties

  • levelmirror
  • subcategorySPI / SPE diamond polish
  • Ra (µm)0.05
  • applies topolymer

Second life

reversibilityzero on the molded part — the mold-cavity surface is transferred at the moment of forming and cannot be undone without re-molding from a different cavity.
blocks substrate recyclingno
renewabilityzero on the existing part; the mold cavity itself can be re-polished or re-textured by the toolmaker for subsequent runs.

SPI / SPE Mold Surface Finish standards (A-1 through D-3); VDI 3400 mold-cavity texture reference plates.

Citations