The short answer
On a CNC RFQ, a global **Ra 0.4 all over** note is not free. Tight roughness on non-functional faces forces fine finishes, polish, or extra passes that widen [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands. Silence on **where Ra applies** is often costlier than the number itself.
This guide is for buyers packaging aluminum and stainless RFQs where drawings scatter Ra notes without a functional map. Illustrations use an **Example part** only—not a customer enclosure. Related notes live in [surface roughness Ra for machined parts](https://3dwk.com/resources/surface-roughness-ra-for-machined-parts) and [as-machined before Type II anodize](https://3dwk.com/resources/as-machined-before-type-ii-anodize); here we focus on **Ra callouts that raise quotes** and how to package them so estimators do not guess.
What Ra callouts mean for quoting
Ra is an average roughness—common CNC bands are Ra 3.2 (typical as-milled), Ra 1.6 (finer mill/turn), Ra 0.8 / 0.4 (fine finish or polish territory depending on process). Process pages for semiconductor and electronics aluminum ([CNC 3-axis Al 6061 semiconductor](https://3dwk.com/en/cnc-3axis/al-6061/semiconductor.html), [CNC 5-axis Al 6061 semiconductor](https://3dwk.com/en/cnc-5axis/al-6061/semiconductor.html), [CNC turning Al 6061 electronics-thermal](https://3dwk.com/en/cnc-turning/al-6061/electronics-thermal.html)) assume localized Ra notes when lots mix sealing lands, cosmetic skins, and heat-spread faces.
Do not bury “smooth finish” inside a notes cloud. Put **Ra 3.2 GENERAL; Ra 1.6 ON SEAL LAND; Ra 0.8 ON DATUM PAD A ONLY** on the PDF and mirror it in RFQ text. Background: [DFM checklist before an online CNC quote](https://3dwk.com/resources/dfm-checklist-before-online-cnc-quote), [what files to send for a CNC quote](https://3dwk.com/resources/what-files-to-send-for-cnc-quote).
Where tight Ra raises bands fastest
Large cosmetic faces at Ra 0.4, deep pockets that need polish access, and turned journals that also carry tight runout all add minutes. Soft stock (PA66 time coeff ×0.8) still needs clear Ra maps on sealing faces. Harder alloys (17-4PH ×1.4, IN718/IN625 ×2.5) amplify fine-finish tool wear; aggressive “Ra 0.4 all over + hard alloy” asks frequently auto-route toward **needs_manual** when mid-line bands exceed planning thresholds under **rates.v1.1** estimates.
If anodize or chem film follows, say whether Ra is measured before or after finish—coatings change texture. Related: [how anodize choice changes CNC RFQ cost](https://3dwk.com/resources/how-anodize-choice-changes-cnc-rfq-cost), [chem film vs Type II anodize](https://3dwk.com/resources/chem-film-vs-type-ii-anodize-aluminum).
Bar $/kg planning bands (estimates only): PA66 ~5, 17-4PH ~9, IN718 ~55. Material cost is rarely the Ra story—area × finish class is.
Functional vs cosmetic Ra
Seal lands, bearing journals, and optical/thermal interfaces earn tight Ra. Hidden structural walls usually do not. Workholding can witness on fine faces—see [soft jaws vs vise CNC production lots](https://3dwk.com/resources/soft-jaws-vs-vise-cnc-production-lots) and [how workholding changes a CNC quote](https://3dwk.com/resources/how-workholding-changes-cnc-quote). Edge breaks interact with fine finishes—see [edge break chamfer deburr callouts](https://3dwk.com/resources/edge-break-chamfer-deburr-callouts-cnc).
Tolerance and inspection traps
Calling Ra without a measurement method note (contact vs optical) or demanding 100% Ra maps on every face fights automatic bands. Default non-critical envelope to ISO 2768-m with typical as-machined Ra; put functional Ra only where needed. Related: [GD&T callouts that raise CNC quote bands](https://3dwk.com/resources/gdandt-callouts-that-raise-cnc-quote-bands), [CMM sampling plans for CNC lots](https://3dwk.com/resources/cmm-sampling-plans-for-cnc-lots), [O-ring groove callouts on CNC housings](https://3dwk.com/resources/o-ring-groove-callouts-cnc-housings).
Illustration 1 shows an **Example part** with general Ra 3.2, a seal land at Ra 1.6, and one pad at Ra 0.8—Example part only.
Example part walkthrough
**Example part:** 6061-T6 plate ~150×100×15 mm electronics cover, seal land around a connector window, one thermal pad face, ISO 2768-m general. With STEP + **Ra 3.2 GENERAL; Ra 1.6 SEAL LAND; Ra 0.8 THERMAL PAD; MEASURE AS-MACHINED BEFORE TYPE II**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “Ra 0.4 everywhere / mirror finish” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“fine finish all faces”) versus a labeled Ra map and the clearer estimate path.
Cosmetic skins that will be painted or powder-coated rarely need ultra-fine as-machined Ra; the coating dominates feel. Say **AS-MACHINED Ra OK UNDER COAT** when that is the intent, so estimators do not price mirror finishes that disappear under paint—related finishing notes live in [powder coating vs painting metal parts](https://3dwk.com/resources/powder-coating-vs-painting-metal-parts) when coating is in scope.
What widens bands fastest
Global ultra-fine Ra, polish on inaccessible pockets, Ra after coating without saying so, and 100% profilometer of every face. Quantity breaks help unit minutes but do not erase finish area—see [how quantity breaks change CNC unit cost](https://3dwk.com/resources/how-quantity-breaks-change-cnc-unit-cost) and [what needs_manual means](https://3dwk.com/resources/what-needs-manual-means-preliminary-quote).
What to do next
Map **general vs functional Ra**, name measure stage (before/after finish), then upload on [quote-new.php](https://3dwk.com/quote-new.php). Service pages: [CNC machining](https://3dwk.com/cnc-machining-service.php), [materials](https://3dwk.com/materials.php). Treat **rates.v1.1** min/mid/max as estimates, not invoices. If the UI shows **needs_manual**, answer the Ra-map questions rather than forcing a fake firm price.
Common questions
Is Ra 3.2 good enough for most CNC parts?
Often yes for non-sealing structures under **rates.v1.1** estimates. Tighten only where function needs it.
Does Ra 0.4 always mean polish?
Not always—some turned or fine-milled faces can land near that band—but large milled areas at Ra 0.4 usually imply extra process. Say the intent.
How does anodize change Ra notes?
Measure stage matters. Dye and thickness alter texture—state before vs after Type II.
Should seal glands get their own Ra line?
Yes. Gland lands are classic functional Ra zones—see [O-ring groove design CNC housings](https://3dwk.com/resources/o-ring-groove-design-cnc-housings) and localized Ra maps on this page.