VDI 33 Surface Finish: Ra Reference & Plaque Guide

VDI 3400 GRADE GUIDE · PHYSICAL COMPARISON

For a visibly coarse finish, appearance and release need joint review. The same grade name should not be treated as a promise of identical tactile feel across different resins or suppliers.

Published grade on this site: VDI 33  ·  Indicative comparison value: Ra 4.50 µm

This Ra figure matches the widely published Charmilles/Agie-derived VDI 3400 comparison chart, cross-checked here against an independent EDM reference-standard supplier's published specification (see citations below), not only against this site's own material. It is an indicative comparison value, not a licensed-standard quotation, gloss measurement, texture-depth conversion, guaranteed molded appearance, or contractual tolerance. If another document (for example a downloadable PDF) shows a different rounded figure, treat this page as the controlling reference until confirmed otherwise with your supplier.

How to evaluate VDI 33

Coarser finishes should be reviewed with the moldmaker for geometry, draft, and release considerations. VDI 33 is a common automotive-interior callout, chosen as much for scratch-hiding as for pure appearance. Confirm which of those two goals is actually driving the specification, since they can call for different acceptance checks.

Before you specify this grade

Compare VDI 30 and VDI 33 on a physical reference, then make a production-resin trial on representative geometry.

  • Mark exactly which faces receive the texture and note the direction of draw.
  • Name the physical master and confirm its material and condition.
  • Approve appearance on a molded sample using the production resin and color.
  • Define the measurement method and acceptance limits if Ra is contractual.
Question to settle with your team:
Do design and tooling agree on both the visible grain and the release risk?

Compare adjacent grades

Compare VDI 30Compare VDI 36

Look at the reference plaques together rather than relying on a phone or monitor image. The physical plaque helps align design, tooling, purchasing, and inspection; a production-material trial remains necessary for final appearance approval.

Need the physical reference?

Review the available VDI reference plaques and confirm which scale or material version covers your target grade before ordering.

See VDI reference plaques View the complete VDI 12–45 guide