3D Print Post-Processing: A Complete Overview of Your Options

You pulled a part off the printer and it looks… fine. Layer lines everywhere, a rough patch where the supports were, maybe a blob or two where the nozzle paused too long. That’s normal. Almost no FDM print is ready to use straight off the bed, and even resin prints need at least a wash and a cure before they’re done.Post-processing is everything that happens between “print finished” and “part ready,” from a five-minute pass with flush cutters to a multi-day paint job. This guide walks through the main categories so you know what exists and which direction to go for your project. Two of the techniques below, sanding and painting, get their own dedicated guides on this site if you want the full walkthrough.## Why Bother Post-Processing at AllThere are four real reasons to spend extra time on a finished print, and most projects only need one or two of them.**Looks.** Layer lines are the most obvious giveaway that something was 3D printed. Smoothing and painting turn a hobby project into something that reads as finished, useful for props, display pieces, or anything on a shelf.**Strength.** Some steps aren’t cosmetic at all. Threaded inserts and properly glued multi-part joints can make a functional part noticeably tougher than it came off the bed.**Sealing.** FDM prints are never fully watertight on their own, even at high infill. Vapor smoothing and epoxy coatings close up the microscopic gaps between layers if a part needs to hold liquid or resist moisture.**Fit and assembly.** Multi-part prints often need holes cleaned up, threads cut, or inserts added before they’ll actually bolt together right. Skip this and you end up forcing a screw into a hole that’s 0.2 mm too small.Not every print needs all of this. A bracket hidden inside an enclosure doesn’t need paint. A display miniature doesn’t need threaded inserts. Match the technique to the job.## The Main Techniques, One at a Time### Support Removal and CleanupThis is the step everyone does whether they think of it as “post-processing” or not. Pull off the raft, snip away the support structures, and knock down any obvious blemishes like elephant’s foot at the base or stringing between features.Flush cutters do most of the work. For supports touching the model directly, grip close to the attachment point and twist as you pull, which tends to shear the support off cleanly at its break point rather than tearing the surface. A hobby knife handles the leftover nubs. This step alone takes a print from “obviously printed” to “recognizable,” even before any sanding.### SandingSanding knocks down layer lines and support scars so the surface reads as smooth instead of ridged. Short version: start coarse (150 to 220 grit), step up through progressively finer grits, and do it wet whenever you can. Water keeps the sandpaper from clogging with plastic dust and gives a more even scratch pattern than sanding dry.This is one of the two techniques we’ve written a full guide on, so check our dedicated sanding guide for grit progressions and material-specific tips across PLA, PETG, and resin.### Filler PrimerFiller primer is a thick, sandable spray primer built to fill in shallow layer lines rather than just sit on top of them. Spray a coat, let it dry, sand it back, and repeat until the surface stops showing texture under raking light. It’s the step most people skip, then wonder why their paint job still shows every layer line underneath.### PaintingPainting is where a print stops looking like a print and starts looking like whatever it’s supposed to be: a prop, a model, a piece of art. It’s also the technique with the most room to get wrong. Wrong primer, wrong paint type for the plastic, no clear coat, and the job looks patchy or starts flaking within a week.We cover the full process (primers, paint types, layering, sealing) in a separate painting guide on this site. Short version: prime first, always seal your final coat, and match your paint chemistry to your plastic so it doesn’t react with the surface.### Acetone Vapor SmoothingThis one’s for ABS and ASA only. Never try it on PLA; PLA doesn’t dissolve in acetone the same way, and you’ll just end up with a gummy, uneven mess.The idea is simple: acetone vapor slightly dissolves the outer layer of the print, which flows just enough to fill in the ridges between layers, then re-hardens as the vapor clears. Done right, it gives ABS parts a glossy, almost injection-molded look in minutes.The safety part is not optional. Acetone’s flash point sits around minus 20 degrees C, meaning it can ignite at essentially any room temperature, and its vapor is heavier than air, so it pools at floor level instead of dispersing. Do this outdoors or with serious ventilation, wear a respirator rated for organic vapors along with gloves and eye protection, and keep every ignition source, pilot lights and space heaters included, well away from your setup.### Epoxy and Resin CoatingsFor a glass-like, glossy finish that also adds UV and chemical resistance, a clear epoxy or resin coating (XTC-3D is the product most makers reach for) goes on after sanding and priming. These coatings level themselves out as they cure, filling fine scratches and adding a depth to the finish that paint alone doesn’t achieve. They’re common on cosplay props and resin-printed miniatures.Formlabs’ finishing guidance for SLA resin parts recommends applying spray coatings only after the part has been thoroughly sanded, since leftover texture will still show through a clear coat. Same logic applies to FDM parts getting an epoxy finish: the coating shows off whatever surface is underneath, good or bad.### Drilling, Tapping, and Heat-Set InsertsPrinted threads work for low-stress, one-time assembly, but they wear out fast under repeated screwing and unscrewing. That’s where heat-set inserts come in: small brass inserts with external ridges that you press into a slightly undersized hole with a heated soldering iron tip. The heat softens the plastic just enough for it to flow around the ridges, then it cools and locks the insert in place, giving a durable metal thread instead of a plastic one.Quick reference: design the hole slightly smaller than the insert’s outer diameter, heat the insert with a low-temperature tip, and press it in slowly and straight so it doesn’t cant sideways. Tapping plastic directly works for lighter-duty jobs, but if the part gets assembled and disassembled repeatedly, an insert will outlast a tapped hole by a wide margin.### Gluing Multi-Part PrintsBig models often get split into pieces to fit the build plate, which means gluing is part of the plan from the start. Cyanoacrylate glue (superglue) works fine for small, low-stress joints and sets in seconds. For bigger structural bonds, a two-part epoxy gives more working time and a stronger joint. On ABS specifically, you can also solvent-weld pieces together using acetone, which melts the two surfaces into each other rather than just gluing them, so the bond becomes part of the print itself rather than a separate joint.Whichever adhesive you use, dry-fit the pieces first. Glue doesn’t fix a bad fit, it just locks in whatever gap you had going in.## Matching the Technique to the PartBefore picking a process, figure out what category the part falls into. **Decorative pieces** (miniatures, props, display models) benefit most from the full chain: sand, prime, maybe smooth, paint, seal. **Functional parts** (brackets, enclosures, tool holders) usually just need cleanup and maybe a coating if they’re exposed to weather or chemicals. **Assembly parts** (anything with screws, multi-part builds, moving joints) need drilling, tapping, or inserts before anything cosmetic happens, since sanding and painting won’t fix a hole that’s misaligned.A lot of real projects mix all three, one bracket that needs an insert and a coat of paint, for instance. That’s fine. Just work through the steps in an order that doesn’t undo earlier work.## A Logical Order to Work InDoing these steps out of sequence usually means redoing one of them. A rough order that works for most projects:1. Remove supports and clean up obvious defects 2. Rough sand to knock down major layer lines and support marks 3. Drill, tap, or add inserts if the part needs them (before painting, not after) 4. Apply filler primer and sand again with finer grit 5. Paint or apply your chosen coating 6. Seal with a clear coat if the finish needs protectionAcetone vapor smoothing usually replaces steps 2 through 4 for ABS parts going for that glossy, injection-molded look, since it’s smoothing chemically instead of mechanically. Gluing multi-part assemblies typically happens either right after cleanup, if you’re painting the whole assembly, or right before painting, if it’s easier to paint the pieces first.## Safety Basics Across the BoardA few habits carry across almost every technique here. Work in a ventilated space, especially for spray primer, paint, or solvents. Wear nitrile gloves when handling resin, epoxy, or acetone. A basic particulate mask covers sanding dust, but switch to a proper respirator with organic vapor cartridges for anything involving solvents or spray finishes. If acetone or any flammable solvent is involved, keep it away from open flames, pilot lights, and anything that sparks. None of this needs to be intimidating, it’s mostly common sense once you know which technique calls for what.## Where to Go From HereSanding and painting are deep enough topics that they each get their own guide on this site. If your next print just needs cleanup and a quick sand, start there. If it’s going to end up painted, that guide covers primers, paint types, and sealing in more depth than this overview does. For anything involving ABS and acetone, treat the safety section above as the minimum, not a suggestion.

A few more specialized techniques sit outside the six-step order above and get their own guides: annealing for extra heat resistance, polishing for real gloss once sanding stalls out, and laser engraving for adding text or logos after the fact.