VDI 12 Surface Finish: Ra Reference & Plaque Guide

VDI 3400 GRADE GUIDE · PHYSICAL COMPARISON

A subtle texture can be difficult to judge from a compressed image. Compare the plaque under the lighting used for design review, then confirm with a molded sample in the production resin.

Published grade on this siteVDI 12 Indicative comparison value Ra 0.40 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 12

Fine-side finishes can be visually subtle; assess them under controlled, representative lighting. VDI 12 sits at the smoothest end of the 12-grade set, so the difference from a fully polished surface can be easy to miss on a monitor. Judge it beside both a polished (non-textured) reference and VDI 15 before approving.

Before you specify this grade

Compare VDI 12 beside VDI 15. Record the viewing distance, light source, resin grade, color, and approved physical reference.

  • 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:
Will the fine texture remain visible in the actual resin, color, and lighting?

Compare adjacent grades

Compare VDI 15

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

Reference and limitations

The VDI official catalog describes VDI 3400 as a guideline on electrical discharge machining. The Ra value here is reproduced as an indicative supplier comparison value, not represented as a certification or a complete statement of the licensed guideline. Published charts can vary in rounding. Agree the applicable reference and measurement procedure before contractual use.

Supplier information only. No VDI endorsement or certification is implied. Validate the selected finish on the actual tool and molded part.

Content last reviewed: 2026-09-24.