Post-processing¶

What to do with a print after it comes off the bed — removing supports, sanding, priming and painting, chemical smoothing, annealing, coating, installing inserts, and gluing parts together. Several of these steps involve flammable solvents, heat or resins: read the safety notes in each section and the Safety page first.

Starting points

Times, temperatures and grit numbers below are starting points from the manufacturer and guide sources listed at the bottom. Where sources disagree the range covers them. Always test on a scrap print or offcut of the same material before working on the real part.

Support removal & cleanup¶

Pull supports while the part is still slightly warm, or after it has fully cooled — whichever your material releases cleanly at. Work away from yourself; supports snap suddenly.
Tools: flush cutters, needle-nose pliers, a deburring tool for hole edges, a hobby knife with a fresh blade (cut away from your hands), and small files.
Scars on supported faces are normal. Knock them back with a file or coarse sandpaper before the sanding sequence.
Stringing and blobs — a quick pass with a heat gun on low melts fine wisps away; keep it moving or thin walls will sag.
Fewer scars start in the slicer: support Z distance, interface layers and tree supports — see Print settings → Supports. Dissolvable supports (PVA/BVOH/HIPS) leave no scars at all — see Filaments → Support materials.

Sanding¶

Work coarse → fine, and don't skip more than about one grade at a time or the scratches from the coarse paper never come out.

Stage	Grit	Purpose
Remove	120–220	Support scars, blobs, heavy layer lines
Smooth	220–400	Layer lines; ABS tolerates starting at 240–320
Refine	400–600	Before primer, or between primer coats
Polish	800–2000	Clear or unpainted gloss finishes

Wet sanding from about 400 grit up cuts dust, keeps the paper from clogging, and keeps the part cool. Dry thoroughly between grits.
Heat is the enemy of PLA. Power sanders and rotary tools generate enough friction heat to smear or gouge PLA — sand by hand, or use light pressure and keep moving. Even aggressively sanding body filler on a PLA part can soften it (Polymaker).
Wear a dust mask — sanding plastic and fillers makes fine dust.
Sanding sticks, foam-backed pads and needle files reach detail that flat paper can't.

Filler, priming & painting¶

Fill¶

Filler primer (a high-build spray primer) is the main tool for layer lines: spray, let it cure, sand it back, repeat until smooth. Polymaker sands primer filler at 800–1200 grit between coats; Raise3D suggests 2–3 thin coats.
Spot / glazing putty for small pits and seams; body filler for large gaps and seams on split parts.
On ABS, an ABS-in-acetone slurry fills seams and sands like the part itself — see Gluing.

Prime¶

Clean the part first — dust, oils and support residue stop paint sticking (compressed air, a tack cloth, or an IPA wipe).

Material	Primer advice	Source notes
PLA	Optional — acrylics bond directly; use filler primer to hide lines	Golden's acrylic test: excellent adhesion without primer
PETG	Optional — acrylics bonded excellently unprimed; some primers reduced adhesion	Golden's test; scuff-sand glossy faces
ABS / ASA	Plastic adhesion primer	Golden's test: weaker unprimed; plastic adhesion primer worked best
Nylon (FDM)	Plastic adhesion primer needed	Golden's test
TPU / flexibles	Plastic adhesion primer; flexible paints	Polymaker: rigid acrylics crack when flexed

Water-drop test

Not sure whether a primer is needed? Put a drop of water on the part. If it beads up, paint will bead too — use a plastic adhesion primer (Golden).

Paint¶

Spray primer and paint in light, even coats from about 15–30 cm (6–12 in) — several thin coats beat one thick one, which runs and buries detail. Allow the label's recoat time; Polymaker allows primer ≥ 2 h before painting.
Acrylics (water-based) are the default for hand painting — quick-drying and easy to clean up. Enamels and lacquers give a harder gloss but need solvents and more ventilation (Raise3D).
Use primer and paint from the same system where possible to avoid incompatibility (Formlabs).
Finish with a matte, satin or gloss clear coat to protect the paint. Formlabs suggests letting paint harden for a week before heavy handling.

Spraying

Spray outdoors or in a ventilated spray booth, wear a respirator rated for paint/organic vapours, nitrile gloves and eye protection, and keep aerosols and solvents away from heat and flames. See Safety.

Vapour smoothing¶

A solvent vapour softens the outer skin of the print so layer lines flow together into a glossy surface. It only works where a solvent dissolves that plastic:

Material	Solvent	Notes
ABS / ASA	Acetone	The classic method; also seals the surface
PVB (e.g. PolySmooth)	Isopropyl alcohol (IPA)	Purpose-made for alcohol smoothing — see Filaments
PLA, PETG	None practical	Acetone is ineffective on PLA (Raise3D); sand and prime instead

Solvent vapour is a fire and health hazard

Acetone has a flash point of about −18 °C (0 °F) and a lower explosive limit of 2.5 % in air (NIOSH). IPA flashes at about 12 °C (53 °F), LEL 2.0 %. At room temperature both give off enough vapour to ignite from a spark.
Work outdoors or in a strongly ventilated space, never in a living area. No flames, cigarettes, gas appliances, heaters, or sparking electrics (switches, motors, thermostats) nearby. Keep a suitable fire extinguisher to hand (see Safety → Fire safety).
Never heat solvent over a flame or a hob, and never seal a heated container — vapour pressure can burst it (MatterHackers).
Don't breathe the vapour. Wear an organic-vapour respirator, solvent-resistant gloves and eye protection. NIOSH's 8-hour exposure limit for acetone is 250 ppm; for IPA, 400 ppm.
Store solvent in its original closed container, away from the printer.

Cold vapour (recommended)Heated vapour (higher risk)IPA for PVB

The slower, safer method — no heat source.

Line a glass or metal container that has a lid with paper towel and dampen it with solvent (no pooled liquid touching the part).
Stand the print on a small non-reactive platform (glass, metal, foil) so it doesn't touch the wet towel.
Close the lid loosely and leave it. Check every few minutes at first — the process is much slower than heated vapour but easy to stop early.
Remove the part and leave it to dry fully before touching; the surface stays soft for a while.

Polymaker notes that cold vapour baths reduce fire risk. Vapour is heavier than air and sinks, so lower sections smooth faster.

Published guides speed acetone up by warming it: MatterHackers holds a container at about 55 °C on a hot plate for ~15 minutes; Polymaker describes 65–75 °C with 1–3 minute exposures repeated as needed.

This is much faster — and much easier to overdo — and puts a heat source next to a cloud of flammable vapour. Only consider it outdoors, with an electric heat source with no exposed elements or open flame, a vented (not sealed) lid, the part hung above the liquid, and a fire extinguisher ready. MatterHackers lets parts set for ~30 minutes before handling; exposures past ~20 minutes start to blister the surface.

PVB smooths with isopropyl alcohol instead of acetone:

Misting chamber — Polymaker's Polysher nebulises 70–90 % IPA around a rotating part.
Manual — spray or brush a thin coat of IPA, let it dry 15–20 minutes, repeat until smooth.
Polymaker: IPA is less flammable than acetone but still volatile — don't heat it above 40 °C. Smoothing reduces strength and heat resistance, so keep it for cosmetic parts.

Side effects: smoothing rounds sharp edges and fine detail, can close small holes and change fits, and over-exposure can leave the part prone to cracking (Polymaker). Smooth before final dimensions matter, or mask critical features.

Annealing¶

Annealing means heating a finished print above its glass transition and holding it there so the polymer can crystallise (semi-crystalline materials) or relax internal stress (amorphous ones). It can raise heat resistance substantially — at the cost of shrinkage and warping.

Material	Typical cycle	What you gain	What you risk
Standard PLA	~100 °C, ~45 min, cool slowly (CNC Kitchen)	Better heat resistance; small strength gain in XY (+7–16 % in CNC Kitchen's tests)	Up to ~10 % shrink in XY and growth in Z, uneven and hard to compensate; no improvement in layer adhesion
Annealable / HT PLA (e.g. Polymaker HT-PLA Pro)	100 °C; 30–60 min under 4 mm thick, up to 3–6 h at 10 mm	HDT rises from 56 °C to 108 °C (0.45 MPa)	Only 0.3–0.6 % dimensional change — the point of these grades
PETG	Mostly amorphous — no real crystallisation. Polymaker suggests trying ~70 °C right after printing for stress relief	Reduced internal stress, steadier dimensions	Prusament PETG's HDT is 68 °C — go much above and the part sags
Nylon (PA)	80–100 °C for 6–16 h (Polymaker); e.g. 100 °C / 16 h for Fiberon PA6-CF20	Full crystallinity → best stiffness and heat resistance	Slight shrink; part comes out bone-dry and must re-absorb moisture (moisture conditioning) to regain toughness
Polycarbonate (PC)	Into a 90 °C oven straight off the printer, ≥ 2 h, cool slowly (Polymaker)	Relieves stress that causes cracking/delamination	Not a crystallinity gain — heat resistance doesn't jump

Standard PLA's HDT is only about 60 °C (PolyLite PLA TDS) — that's what annealing is trying to fix. Compare materials in the HDT table.

Annealing without ruining the part

Use an oven thermometer — kitchen oven dials can be well off, and an overshoot slumps the part. A preheated oven gives more even results.
Leave the part on its build plate and leave supports on while annealing (CNC Kitchen, Polymaker) — they resist warping.
Some people pack parts in sand or salt for support; CNC Kitchen found it helped but didn't eliminate distortion.
Cool slowly in the switched-off oven.
Anneal a test piece first and measure it; if dimensions matter, pick an annealable grade (see Material selection).
Don't use a food oven for materials that fume, and ventilate — see Safety.

Epoxy coating¶

A thin coat of two-part epoxy fills layer lines, gives a hard glossy surface, and seals the part.

Coating resins made for prints (e.g. Smooth-On XTC-3D) self-level into a thin film. XTC-3D mixes 2 A : 1 B by volume (100 : 42 by weight), has a ~10 minute pot life, is tack-free in ~2 h and cured in ~3.5 h at 23 °C; keep each layer under ~0.4 mm (1/64 in). One thin coat suits most prints; recoat when the previous coat is "tacky hard".
Tabletop / bar-top epoxy works too but cures slower and thicker; follow its own datasheet for ratio and layer thickness.
Brush with a disposable chip brush or foam brush, keep working the surface until it starts to set to avoid runs, and do intricate parts one section at a time. Pour mixed epoxy into a shallow tray to slow the reaction.

Epoxy hazards

Mixed epoxy is exothermic — a large mass in a cup can get hot enough to melt the cup, burn skin, or ignite combustibles. Mix only what you can use; if it starts heating up, move it outdoors (Smooth-On).
Wear nitrile gloves and eye protection and work ventilated; avoid skin contact and fumes (Smooth-On). Prusa warns that liquid epoxy is toxic. Don't speed the cure with heat on prints near their softening point.

Coating does not make a print food-safe

An epoxy coating only helps with food contact if that specific epoxy is certified for food contact and is fully cured at the correct ratio — under-cured epoxy can be toxic (Prusa). General print coatings such as XTC-3D make no food-safety claim. Coatings also wear through over time, exposing layer lines that trap bacteria. Prusa's own advice: don't use prints as food containers. See Safety → Food contact.

Heat-set inserts¶

Brass threaded inserts melted into a printed hole give a durable metal thread. Size the hole first — see Design for printing → Heat-set insert holes.

Tip: use a dedicated insert tip for your soldering iron (they centre in the insert). Larger inserts (M5+) want a thicker tip for more heat.
Temperature: about 10–20 °C above the print temperature — roughly 225 °C for PLA, 245 °C for PETG, 265 °C for ABS (CNC Kitchen). Too hot degrades the plastic around the insert; be careful with fixed-temperature irons that run hotter.
Press straight: set the insert on the hole and let the iron's weight do most of the work. Keep the iron vertical — a crooked insert means a crooked screw. A press/jig (a soldering-iron holder on a vertical slide, or a drill-press-style stand) makes repeatable, square installs.
Stop at ~90 %: melt the insert most of the way in, remove the iron, then press it flush with a flat tool while it is still hot.
Hold it a few seconds while the plastic re-solidifies — inserts tend to creep back up straight after melting.

Resin prints can't be melted: glue inserts in with thick CA or epoxy instead (CNC Kitchen).

Gluing¶

Prepare every joint the same way: sand the mating faces flat, clean them (IPA), dry-fit, then glue and clamp. Alignment pins or keyed seams in the design (see Splitting large parts) make clamping far easier.

Adhesive	Best for	Notes
CA (super glue), gel	Quick repairs, small or unclampable parts in PLA, ABS, PETG	Gel stays where you put it; thin CA wicks through gaps. Bonds can be brittle
Two-part epoxy	Gap filling, structural joints, mixed materials	Slow set gives time to align; gap-filling
Two-part plastic welder (methacrylate)	High-stress clamped assemblies (Polymaker, PLA)	Needs clamping while it cures
Solvent-type plastic glues	Seamless welds in PLA, PETG, ABS/ASA (material-specific formulas)	Partially dissolve both faces so they fuse (Polymaker)
Acetone (solvent welding)	ABS, ASA	Brush on both faces, press together — fuses the parts into one
Mechanical fixing	Nylon	Polymaker: glues bond poorly to nylon — use screws, clips or inserts

ABS glue and slurry. Dissolve ABS scrap in acetone overnight in a glass or metal jar (MatterHackers):

Glue — about 8 g ABS per 50 ml acetone (white-glue consistency) to weld parts.
Slurry — about 20 g ABS per 50 ml acetone (putty consistency) to fill seams and gaps; sands like the part.

The same acetone fire and fume precautions as vapour smoothing apply.