The short answer
On SLM / laser-powder-bed RFQs, **downskin roughness** is not the same note as a general Ra title-block callout, and it is not a promise that every face will match an upskin coupon. Downskin (down-facing) surfaces typically come out rougher than upskin or vertical walls because the layer is built over powder or sparse support, with more dross and heat at that face. Orientation decides which faces are downskin; a machining stock, a named cosmetic class, or an allowed as-built band is what lets a buyer control the result. Silence on which faces may stay as-built, and on whether a skim or face mill is allowed, is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** / powder estimate bands—not the laser minutes alone.
This guide is for buyers packaging titanium or AlSi10Mg RFQs where CAD shows a sealing or cosmetic face with only “Ra 3.2 all over” and no orientation note. Illustrations use an **Example part** only—not customer flight hardware. Sibling notes live in [SLM build orientation notes](https://3dwk.com/resources/slm-build-orientation-notes-for-buyers) and [SLM support removal and skim notes](https://3dwk.com/resources/slm-support-removal-and-skim-notes); here we focus on **downskin roughness packaging**. We do not publish machine parameter sets or process certificates.
What downskin roughness means for quoting
**Downskin** is the face that looks downward during the build (or sits at a shallow down-facing angle). **Upskin** looks upward; vertical walls are a third family. A single Ra note copied from a [CNC roughness guide](https://3dwk.com/resources/surface-roughness-ra-for-machined-parts) does not tell the shop which of those families may stay as-built. Process pages for aerospace SLM ([SLM Ti-6Al-4V aerospace](https://3dwk.com/en/slm/ti-6al-4v/aerospace.html), [SLM Ti-6Al-4V](https://3dwk.com/en/slm/ti-6al-4v.html), [SLM AlSi10Mg aerospace](https://3dwk.com/en/slm/alsi10mg/aerospace.html)) assume orientation and facing-stock notes when lots mix as-built skins with sealing lands.
Do not bury “smooth as possible, orient as needed” inside a notes cloud. Put **FACE A SEALING: 0.5 MIN FACING STOCK, MACHINED; FACES B–C AS-BUILT DOWNSKIN ALLOWED; ORIENTATION SHOWN ON PDF** on the drawing and mirror it in RFQ text. Background: [DFM checklist before an online CNC quote](https://3dwk.com/resources/dfm-checklist-before-online-cnc-quote) still applies when a skim is planned, and [what files to send for a CNC quote](https://3dwk.com/resources/what-files-to-send-for-cnc-quote) should include the orientation sketch.
Orientation, support, and facing stock
Rotating the part can move a cosmetic face off the downskin, at the cost of support on another wall or a taller build—see [support strategy notes for thin walls](https://3dwk.com/resources/support-strategy-notes-slm-thin-walls) and [recoater clearance notes](https://3dwk.com/resources/recoater-clearance-notes-slm-tall-parts). If a face must hold a sealing Ra or a gasket land, the reliable pack is **additive stock plus a named skim**, not a hope that downskin will match a coupon. Shallow angles (faces that are almost flat-down) often look worse than a steep down-facing wall; if a shallow face cannot take stock, say whether blast, tumble, or as-built is acceptable.
Ti-6Al-4V and AlSi10Mg powder planning bands sit in **rates.v1.1** / powder estimate tables; powder cost is rarely the whole downskin story—orientation, support removal, and whether a CNC skim is in the pack are.
What not to invent on the RFQ
Do not send a laser power, hatch, or layer-thickness recipe and expect that to replace a face class. Shops will use their qualified parameters; buyers should state the **result** (which faces are machined, which may stay as-built, what inspection measures roughness). Do not attach a process certificate you do not have, and do not treat a marketing coupon photo as the as-built downskin on your geometry. [Powder-reuse notes](https://3dwk.com/resources/powder-reuse-notes-slm-buyers) and [build-plate removal](https://3dwk.com/resources/build-plate-removal-notes-slm-parts) can affect nearby faces, but they do not erase a missing downskin class.
Tolerance and inspection traps
Calling “Ra 1.6 all over” on an as-built SLM body, mixing a sealing face with no stock, omitting orientation so every face might be downskin, or asking for 100% roughness traces on every as-built wall, all force **needs_manual**. Default non-functional skins to an as-built or blasted class and put a machined Ra only on named lands. Related: [surface roughness Ra callouts that raise quotes](https://3dwk.com/resources/surface-roughness-ra-callouts-that-raise-quotes), [ISO 2768 general tolerances on CNC RFQs](https://3dwk.com/resources/iso-2768-general-tolerances-cnc-rfq) for the skim, [escape-hole notes](https://3dwk.com/resources/escape-hole-notes-slm-hollow-parts) when a hollow sits under a downskin skin.
Illustration 1 shows an **Example part** bracket with a labeled machined sealing face versus an allowed as-built downskin on the opposite wall.
Example part walkthrough
**Example part:** Ti-6Al-4V SLM bracket ~80×50×35 mm, face A a sealing land with 0.5 mm minimum facing stock, faces B–C allowed as-built downskin, orientation shown with face A up. With STEP + **FACE A: 0.5 MIN STOCK, MACHINED SEALING LAND; B–C AS-BUILT DOWNSKIN OK; ORIENTATION AS SHOWN**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “Ra 1.6 all faces, orient as needed” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“make downskin as smooth as CNC”) versus a labeled face-class pack and the clearer estimate path.
What widens bands fastest
A single tight Ra on every skin, no stock on a sealing face, orientation left to the shop with a cosmetic requirement on all sides, and 100% roughness inspection of as-built downskin. Quantity breaks help unit minutes but do not erase face-class ambiguity—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
Mark each functional face as **machined with stock** or **as-built downskin allowed**, attach an orientation sketch, then upload on [quote-new.php](https://3dwk.com/quote-new.php). Service pages: [3D printing](https://3dwk.com/3d-printing-service.php), [materials](https://3dwk.com/materials.php). Treat **rates.v1.1** / powder min/mid/max as estimates, not invoices. If the UI shows **needs_manual**, answer the downskin questions rather than forcing a fake firm price.
Common questions
Will a downskin face match my CNC Ra coupon?
Usually not as a silent default under **rates.v1.1** / powder estimates. Downskin is typically rougher than upskin or a milled coupon. If you need a sealing Ra, add facing stock and say the face is machined.
Can I write “orient as needed to make all faces smooth”?
That pushes every wall toward upskin or extra support and often still fails on some faces. Pick the faces that matter, then allow as-built or blast on the rest.
When should I add facing stock instead of changing orientation?
When a sealing or datum land must meet a machined Ra, or when rotating the part would create a worse recoater or support problem. Stock plus a skim is the predictable path.
Do I need to send laser parameters with the RFQ?
No. Send the result you need: face class, stock, orientation, and how roughness will be checked. Leave qualified parameters to the shop; do not invent a parameter card or a certificate.