Key Takeaways
- Finishing turns raw prints into production-quality parts.
- Options: sanding, smoothing, painting, dyeing, plating.
- Each adds time and cost — specify what the part needs.
- SLA finishes easier than FDM.
A part that exits a 3D printer is a raw workpiece. Layer lines, support witness marks, porous surfaces — none of these belong on a finished product. Post-processing is what bridges the gap between a prototype and a production-ready component, and at Layer X in Ahmedabad it accounts for up to 40% of total part cost on some orders. Understanding these techniques helps you specify the right finish from day one and avoid expensive surprises.
Sanding and Abrasive Finishing
Wet sanding is the workhorse for FDM and SLA parts. Start at 120–180 grit to knock down layer lines, progress to 400 for blending, and finish at 800–1200 for a near-gloss surface. For SLS nylon, sanding is less effective because the powder-bed fusion surface is more uniform — bead blasting delivers better results at scale.
When to use: Visual prototypes, master patterns before moulding, parts that need paint adhesion. When to skip: Functional parts with tight tolerances (sanding removes 0.1–0.3 mm per surface).
Bead Blasting and Tumbling
Glass bead blasting at 60–80 psi is standard for SLS nylon at Layer X. It removes loose powder, closes surface porosity by ~15%, and produces a consistent matte finish that paint adheres to without primer. Tumbling (vibratory finishing with ceramic media) is used for small SLA resin parts in batches — uniform finish without operator variance.
For metal DMLS parts, shot blasting in steel grit removes support stub witness marks and creates a uniform grey surface with Ra 3–6 µm. Further polishing or electropolishing brings this below Ra 1 µm for medical and fluid-path applications.
Vapour Smoothing (ABS and ASA)
Acetone vapour smoothing chemically dissolves the surface of ABS and ASA FDM parts, reflowing the thermoplastic into a glossy, nearly isotropic surface. Layer lines disappear completely. Surface roughness drops from Ra 15–25 µm (as-printed) to Ra 0.5–2 µm after smoothing.
Critical constraint: Wall thickness must exceed 1.5 mm — vapour smoothing can collapse thin walls. Tolerances shift by 0.05–0.2 mm, so design with this in mind. PA12 SLS parts can be smoothed with EtO or CO₂ vapour, achieving similar results without dimensional loss.
Painting and Coating
FDM and SLA parts accept automotive-grade rattle-can primer and paint well after bead blasting or sanding to 400 grit. For production-quality results, two-part epoxy primers offer superior adhesion and UV stability. DMLS metal parts accept powder coating, anodising (aluminium), electroless nickel, and physical vapour deposition (PVD) coatings.
At Layer X we routinely apply RAL colour matching for customer-facing product prototypes and black oxide + oil for tool steel injection mould inserts.
Dyeing SLS Nylon
SLS PA12 parts are naturally off-white and porous enough to absorb fabric dye. Hot-dye immersion at 80–95°C for 20–40 minutes produces deep, consistent colour across complex geometries including internal channels — something painting cannot achieve. Black is the most popular colour because it hides surface texture variation. Colour penetrates ~0.3 mm, so re-machined surfaces will show white again.
Post-Processing Cost Guide
| Process | Typical surcharge | Best for |
|---|---|---|
| Bead blast only | +8–12% | SLS nylon standard finish |
| Sanding (120→800) | +15–25% | SLA master patterns |
| Vapour smooth (ABS/ASA) | +20–30% | Consumer product appearances |
| Primer + 2-coat paint | +35–55% | Trade show models, renders |
| SLS hot-dye (black) | +10–18% | Production SLS parts |
| Electropolish (DMLS SS/Ti) | +40–70% | Medical, food-contact parts |
Specifying the right finish from the outset avoids costly rework. Contact Layer X to get a finishing quote alongside your 3D printing order, or browse our shop for standard materials and finishes.