VDI 3400 GRADE GUIDE · PHYSICAL COMPARISON
A high grade number signals a rougher position in the comparison scale, not a universal grip or scratch-resistance result. Validate the functional claim on the finished part if function depends on it.
Published grade on this site: VDI 39 · Indicative comparison value: Ra 9.00 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 39
Coarser finishes should be reviewed with the moldmaker for geometry, draft, and release considerations. VDI 39 is frequently requested for functional grip rather than pure appearance. If grip or wear resistance is the real requirement, test it directly on the molded part instead of assuming it from the VDI number.
Before you specify this grade
Separate appearance approval from any grip, wear, or scratch requirement; test the latter on the production material and 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.
Is the requirement visual, tactile, or functional — and has that function been tested?
Compare adjacent grades
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.