Post-Processing 3D Prints: Sanding, Painting, and Finishing

From Printed to Presentable

A part off the printer is rarely the finished product. Layer lines, support scars, and matte thermoplastic surfaces are fine for a fixture, but customer-facing hardware and appearance models deserve better. The good news: 3D printed plastics finish beautifully with ordinary techniques, and knowing the sequence — and which steps your part actually needs — is most of the skill.

The Sanding Ladder

Sanding is the foundation of every quality finish. The grit sequence that works on FDM and SLA alike:

• Start at 120-150 grit only if layer lines are pronounced or support scars need leveling; otherwise begin at 220.
• Progress 220 -> 400 -> 600, wiping dust between grits. Never skip more than one step — deep scratches from a skipped grit reappear under paint.
• Wet-sand from 400 up: water carries away swarf and prevents the gummy melting that dry-sanding causes on PLA and PETG.
• For a polished-plastic look, continue 800 -> 1200 -> 2000, then buff with plastic polish.
• Radiused corners and flat faces sand fast; deep recesses may be better filled and primed than chased with folded paper.

Priming and Painting

Primer is what turns a sanded print into a paint-ready surface: filler primers (high-build automotive types) bridge remaining micro-lines in one or two coats. Sand the primer at 400-600, re-coat thin, and inspect under raking light — primer shows every defect paint would amplify. For color, acrylic and urethane rattle-can systems bond well to all our materials; ABS additionally takes solvent-based paints. Two light coats beat one heavy coat every time, and a clear topcoat (matte or gloss) adds scratch resistance worth having on handled parts.

Vapor Smoothing: The ABS/ASA Superpower

ABS and ASA dissolve slightly in acetone vapor, and controlled exposure melts the outer surface into a sealed, glossy skin with layer lines gone entirely — the closest a printed part gets to looking injection molded with zero sanding. It also seals parts against moisture and bacteria harborage. The tradeoffs: sharp edges soften by a few hundredths of a millimeter, and precision bores should be masked or re-reamed after. PLA and PETG have no comparably safe solvent, which is one more quiet argument for ASA on cosmetic outdoor parts.

SLA-Specific Finishing

SLA parts start life nearly finished — after wash and cure, surfaces are already smooth. Finishing work is lighter: nip support touchpoints with flush cutters, one pass at 400-600 grit on the touchpoint marks, and the part is display-ready. Clear resin deserves a note of its own: sanding through the grits followed by a gloss clear coat produces genuinely transparent windows, light pipes, and fluid-visualization parts.

Functional Post-Processing

Finishing isn't only cosmetic. The functional operations we perform routinely: heat-set threaded inserts (stronger than any printed thread), drilling and reaming bores to true diameter, tapping threads in thick bosses, and bonding large assemblies from plate-sized sections with structural adhesives. Specify any of these in your order notes and the part arrives ready to install.

Order It Finished

Every technique in this guide is available as a service — sanding, priming, painting to a target color, vapor smoothing, inserts, and machining operations. Upload your part, note the finish requirement, and we'll quote the complete job so what arrives in the box is done.