3D Printing 101 Part 9: Post-Processing. Washing, Curing, Sanding, Painting, and Finishing Like a Pro

Part 8 covered slicing: the invisible translation layer between a 3D model and a physical object, where every setting you choose becomes a physical consequence. You learned how layer height, supports, and exposure times shape what comes out of the printer. Now something has come out. It's sitting on your build plate, still warm, maybe still dripping. And here's the thing nobody tells you when they're showing off their prints online: that moment is the beginning of the work, not the end.

Post-processing is where prints go from "technically complete" to actually good. It's unglamorous, it takes time, and it's the step most beginners skip entirely. This guide covers the full pipeline: washing, curing, support removal, sanding, and surface finishing. Whether you're running resin on an Anycubic Photon S or FDM on a FlashForge Inventor, the principles apply. Some steps take three minutes. Others take three hours. Both kinds are worth doing.

Why Post-Processing Is the Step Everyone Skips (And Shouldn't)

The Gap Between 'Printed' and 'Finished'

A raw print is a rough draft. It has all the information, all the geometry, all the intent. But it also has layer lines, support scars, sticky surfaces, and surface artifacts that make it look like exactly what it is: a machine-made object that hasn't been touched by human hands yet. Post-processing is the act of touching it.

Think of it the way you think about writing. A first draft gets the ideas down. Editing makes them land. Nobody publishes a first draft, and nobody should display a raw print if they care how it looks. The print is the draft. Post-processing is the edit.

What Post-Processing Actually Covers

The term covers a wide range of steps, and not all of them apply to every printer or material. For resin prints, washing and curing aren't optional finishing touches. They're mandatory safety and chemical completion steps. Skipping them means handling toxic uncured resin and ending up with prints that are sticky, weak, and structurally incomplete.

For FDM prints, the stakes are lower but the opportunity is real. Sanding, priming, and painting can transform a functional PLA part into something that looks injection-molded. The pipeline this article covers includes: washing (resin only), UV curing (resin only), support removal (both), sanding and surface prep (both), and primer and paint finishing (both). Some of these steps take minutes. Some take an afternoon. None of them are wasted time.

Resin Post-Processing: The Mandatory First Steps

Why Uncured Resin Is Dangerous and What to Do About It

Uncured photopolymer resin isn't just messy. It's a chemical irritant that can cause skin sensitization, respiratory irritation, and in some people, full allergic reactions. The danger isn't dramatic. It's cumulative. A single brief exposure might feel like nothing. Repeated exposures without protection build sensitivity over time, and once sensitized, even small amounts can trigger a reaction. This is not a theoretical risk.

Gloves are non-negotiable. Nitrile gloves, not latex. Resin can permeate latex faster than you'd expect, and some people are already latex-sensitive. Safety glasses matter too, especially when handling the build plate over a resin vat. Ventilation is the third pillar: an open window is better than nothing, but a proper respirator with organic vapor cartridges is the right call if you're printing frequently.

Never pour liquid resin down a drain. Never pour used wash solvent down a drain. Liquid resin in the plumbing is an environmental and legal problem, and it doesn't just disappear.

Tools You Need Before You Even Open the Printer

Before you pull a build plate out of the printer, have these ready: nitrile gloves (doubled if you're clumsy), safety glasses, a silicone mat or disposable surface to work on, paper towels, and your wash station. The author's current setup centers on the Anycubic Wash & Cure Machine, which handles both stages in one unit and makes the workflow significantly cleaner than juggling separate containers.

Drips happen. Resin will get on the build plate handle, on the vat edges, on the side of the printer. Have paper towels within arm's reach before you start, not after you've got resin on your hands and you're looking around the room for something to wipe it on. Preparation here isn't fussiness. It's how you avoid making the workspace unusable for the next session.

Washing Resin Prints: Step-by-Step with the Anycubic Wash & Cure

Choosing Your Wash Solution: IPA vs Dedicated Cleaners

The purpose of washing is simple: remove the uncured liquid resin still clinging to the print surface, pooling in cavities, and hiding inside support structures. If it stays there, it never fully hardens, the surface stays tacky, and fine details stay blurred under a film of sticky polymer.

Isopropyl alcohol (IPA) at 90% concentration or higher is the standard. It's widely available, inexpensive, and effective on most consumer resins. The critical word is "higher." 70% IPA, the kind sold for first aid, has too much water content to clean resin efficiently. It'll work in a pinch, but it's slower and leaves more residue.

Dedicated resin cleaners like the Anycubic Wash Solution are formulated specifically for photopolymer resins. They tend to be gentler on prints, less prone to causing brittleness with extended exposure, and often more effective on ABS-like resins that IPA struggles with. The tradeoff is cost. For high-volume printing, IPA is more economical. For precision work or expensive resins, dedicated cleaner earns its price.

The Washing Process: Settings, Timing, and Technique

With the Anycubic Wash & Cure, the process is straightforward. Fill the wash basket to the indicated fill line with your chosen solution, place the print (still on the build plate or removed, depending on your preference), set the timer, and run the cycle. The machine's internal agitation does most of the work.

Timing matters in both directions. Under-washing leaves resin residue that prevents clean curing. Over-washing is a real problem too: extended IPA exposure makes prints brittle, clouds translucent resins, and can cause surface crazing on detailed miniatures. Set a timer. Don't walk away and come back twenty minutes later.

After the wash cycle, remove the print and let it air-dry completely. Do not move to curing while the surface is still wet with solvent. Trapped IPA under UV light doesn't cure cleanly, and solvent vapor inside hollow prints can cause pressure issues during curing.

What to Do When You Don't Have a Wash Machine

Two containers and a soft brush. That's the manual method. Container one holds fresh IPA for the initial agitated rinse, where you submerge the print and swirl it. Container two holds slightly used IPA for a second gentler rinse. A soft-bristle toothbrush handles recessed details, support attachment points, and any area where resin tends to pool.

The two-container method extends the life of your IPA by keeping the dirtiest wash separate from the final rinse. It's slower than a machine, but it works. The toothbrush tip isn't optional for detailed prints: support bases, undercuts, and text embossing will trap resin that agitation alone won't reach.

Curing Resin Prints: Locking In Strength and Surface Quality

How UV Curing Works and Why It Matters

During printing, the UV light source inside the printer partially polymerizes the resin, layer by layer, just enough to solidify it. The print holds its shape, but the chemical reaction isn't complete. Post-curing finishes that reaction by exposing the cleaned, dry print to sustained UV light, triggering the photoinitiators left in the resin to complete the crosslinking process.

The result is harder, stronger, and more chemically stable than the as-printed state. An under-cured print is rubbery, prone to warping over time, and can leach uncured monomer. An over-cured print becomes brittle, yellows faster, and loses the slight flex that makes some resin types useful. Both extremes are worth understanding.

Under-cured prints feel slightly flexible when they shouldn't, have a tacky or waxy surface after washing, and may show white stress marks when bent. Over-cured prints are chalky, crack at thin sections, and look faded. Neither is what you want.

Using the Anycubic Wash & Cure Machine for Curing

After the print is fully dry, flip the Anycubic unit to curing mode. The turntable rotates the print under the UV array for even exposure. Place the print on the turntable without the basket, set your time, and run the cycle.

Cure times vary by resin type and print mass. Standard resins typically cure in two to four minutes under a dedicated station. ABS-like resins need longer, often four to six minutes. Flexible resins are the outlier: over-curing makes them stiff and defeats the purpose, so shorter cycles and manufacturer specs matter more here.

Curing Times, Temperatures, and the Warm Water Trick

Submerging prints in warm water (around 40°C) during UV exposure is a technique that improves surface hardness and reduces surface tackiness. The warmth accelerates the photoinitiator reaction slightly, and the water acts as a medium that helps distribute UV light more evenly around curved surfaces. It's not magic, but it's a meaningful improvement on prints that need a particularly clean surface finish before painting.

Sunlight curing works. It's free. It's also inconsistent in ways that matter: cloud cover, time of day, season, and glass filtering all affect UV intensity. A UV nail lamp is a reasonable budget alternative to a dedicated station. Just expect longer cure times, uneven exposure on complex geometry, and the need to rotate prints manually.

Support Removal: The Art of Not Breaking Your Print

When to Remove Supports: Before or After Curing?

This question has a real answer, and it depends on what the supports are doing. The argument for removing before final cure is that partially cured resin has flex. Supports bend and pull away cleanly rather than snapping and taking a chunk of the print surface with them. The argument for removing after curing is that fully cured resin has defined break points at the support tips, which in theory means cleaner separation.

In practice, on the Anycubic Photon S, the better approach is a hybrid: remove the majority of supports before the final cure cycle, especially the fine ones on detail areas where a snap could damage surface geometry. Leave structural supports, the ones bracing large flat sections or overhangs under real mechanical stress, until after curing. Then remove those with more confidence in where the break will happen.

Tools and Techniques for Clean Support Removal

Flush cutters are the primary tool. Get a dedicated pair for resin work and keep them sharp. A dull cutter crushes rather than cuts, leaving a worse scar than a clean snap. Dental picks and hobby knives handle the fine work: scoring around support bases, lifting support rafts, and cleaning up the attachment point before it's fully hardened.

The technique for resin supports is a twist-pull, not a straight pull. Grip the support close to its base on the print, rotate slightly to break the adhesion at the tip, then pull. Straight pulling drags the support tip across the surface and leaves a longer scar. The twist-pull concentrates the break at the contact point.

For FDM prints on the FlashForge Inventor, PLA supports snap off with much less drama. They're stiffer, the layer adhesion between support and print is intentionally weak, and a pair of needle-nose pliers handles most of them. PVA supports (if you're running dual extrusion) dissolve in warm water, which is the cleanest option of all.

Dealing with Support Scars and Witness Marks

Witness marks are normal. Every support leaves something: a small bump, a shallow divot, a slightly rough patch. They're not failures. They're the cost of printing geometry that needed support. The question is what you do with them.

Small bumps from support tips sand down quickly with 220-grit paper. Divots need spot putty before sanding. Score around the edge of the scar with a hobby knife before pulling a support if you want a cleaner break point to start from. The sanding and filling steps in the next section handle what's left.

Sanding and Surface Finishing: From Rough to Smooth

Sanding Resin Prints: Grit Progression and Wet Sanding

Sanding a resin print is precision work. The geometry is often complex, the details are fine, and aggressive sanding removes the things you spent hours printing. The principle is grit progression: start coarse enough to remove what needs removing, then work up through finer grits until the surface is where you want it.

For resin, start at 220 grit to address support scars and obvious surface artifacts. Move to 400, then 800, then 1200 or higher if you're chasing a smooth finish before paint. Each stage removes the scratches left by the previous one. Skipping grits means the coarser scratches survive under a surface that looks finer than it is, and they show up under paint.

Wet sanding is the technique for fine grits on resin. Dip the sandpaper in water, sand in small circular motions, rinse frequently. The water reduces friction, prevents the paper from clogging with resin dust, and keeps heat from building up in the print surface. It also keeps resin particles out of the air, which matters for the same respiratory reasons that apply to uncured resin handling.

Sanding FDM Prints: Working with Layer Lines

FDM layer lines are a different challenge. They're regular, predictable, and run perpendicular to the print direction, which means they sand consistently. Start at **120

Painting and Coloring Your Prints

You've washed it, cured it, sanded it smooth. Now comes the part that transforms a grey lump of resin or a striped FDM print into something people actually stop to look at. Painting is where post-processing becomes craft.

Primer: The Step You Cannot Skip

Primer does two things. It gives paint something to grip, and it tells you exactly where your surface still needs work. Skip it and your paint will peel, chip, or look uneven no matter how carefully you apply it. Apply it and you'll immediately see every scratch, seam, and low spot you missed during sanding.

For large flat surfaces, spray primer is the right call. A few light coats from a rattle can gives even coverage without brush marks. For small detailed miniatures or intricate geometry, brush-on primer gets into recesses that spray misses entirely. Use grey primer as your default. White primer makes colors pop. Black primer deepens shadows naturally.

Brush Painting vs Airbrushing vs Rattle Cans

Rattle cans are fast and forgiving. They're excellent for base coats and primer layers, and a decent rattle can finish is genuinely good enough for display pieces. Brush painting gives you control. You can work color into specific areas, blend transitions, and fix mistakes with a damp cloth. It requires patience but zero equipment investment beyond the brushes themselves. Airbrushing produces results that look factory-applied. Smooth gradients, precise coverage, zero brush marks. The investment is real, though: a decent airbrush setup runs $80 to $200 before you buy compressor and cleaning supplies.

Most hobbyists start with rattle cans and brushes, then add an airbrush once they've caught the bug. That's a completely sensible path.

Acrylic Paints, Washes, and Dry Brushing for Detail

Acrylic paints are the right choice for almost every hobbyist application. They're water-based, so cleanup is easy, they dry fast, and the selection is enormous. Vallejo paints are widely respected for their consistency and dropper bottles. Citadel paints from Games Workshop are expensive but formulated specifically for miniature work. Apple Barrel craft acrylics from any craft store cost almost nothing and work fine for larger prints where you don't need fine detail.

Washes are thin, heavily diluted dark paint. You brush them liberally over a surface and they flow into every recess, pooling in recesses and panel lines. The result is instant depth and shadow. A single wash pass over a primed and base-coated print makes it look like you spent twice as long painting it.

Dry brushing is the opposite technique. Load a stiff brush with paint, then wipe almost all of it off on a paper towel until barely any remains. Drag that near-dry brush lightly across raised edges and surfaces. The tiny amount of paint left deposits on high points and catches every edge, creating highlights that make detail pop.

Seal everything when you're done. A matte varnish kills shine for a realistic look. Satin varnish sits in the middle. Gloss varnish is right for anything that should look wet, polished, or metallic. Two light coats protect the paint job from handling and give the piece a finished, intentional look.

FDM-Specific Finishing Techniques

Resin prints come off the build plate with smooth surfaces that just need cleanup. FDM prints come off with visible layer lines, and getting rid of them takes different tools depending on what filament you used.

Acetone Smoothing for ABS Prints

Acetone vapor smoothing is the one technique that genuinely feels like magic. Place an ABS print inside a sealed container with a small amount of acetone-soaked paper towel at the bottom. Don't let the print touch the acetone directly. The vapor fills the container and slightly melts the outer surface of the print, fusing the layer lines into a smooth, shiny finish.

The result is dramatic. A print that looked like a topographic map comes out looking injection-molded.

This technique works only on ABS. It does nothing useful for PLA, PETG, or PLA+. If you're printing on a FlashForge Inventor, which primarily runs PLA and PLA+, acetone smoothing isn't available to you without switching filaments.

Epoxy Coating for a Glass-Smooth Surface

XTC-3D and similar brush-on epoxy coatings work on PLA, ABS, and most common filaments. You brush on a thin coat, and the self-leveling formula flows into layer lines and fills them as it cures. Two thin coats produce a surface that looks nearly cast rather than printed. It adds a small amount of weight and slightly softens fine detail, so it's better suited to larger prints than intricate miniatures.

Heat Gun and Flame Polishing Tips

A heat gun passed carefully over a PLA print can reduce layer line visibility by slightly softening the surface. The key word is carefully. Too much heat warps the print in seconds. Keep the gun moving constantly and work in short passes from a distance of at least 15 centimeters.

Flame polishing uses a quick pass from a butane lighter or torch to achieve a similar effect on PLA. The technique requires an extremely light touch. One slow pass and you've melted the surface. Always test both techniques on a scrap piece of the same filament before touching your actual print.

Assembly: Putting Multi-Part Prints Together

Build volumes have limits. A 300mm tall figurine won't fit on most consumer printers, but it will fit if you split it into sections. Multi-part printing also lets you orient each piece for optimal layer strength, print complex geometry that would otherwise require impossible support removal, and design modular objects that ship or store flat.

The challenge is making the seams disappear.

Adhesives: Which Glue for Which Material

The right adhesive depends entirely on the material.

CA glue (cyanoacrylate, or super glue) is the standard choice for resin and PLA. It bonds fast, holds well, and is easy to find. Use medium viscosity for most joints; thin CA wicks into tight-fitting seams and bonds almost instantly. Epoxy is slower but stronger, making it the right call for structural joints that will bear load or stress. Plastic cement works on ABS by chemically welding the surfaces together. Flexible adhesive like E6000 is the right choice for TPU parts that need to flex at the joint without cracking.

Regardless of adhesive type, roughen the mating surfaces lightly with 120-grit sandpaper first. It takes ten seconds and meaningfully increases bond strength.

Mechanical Fasteners and Press-Fit Joints

Press-fit joints use precise tolerances to hold parts together through friction alone. A typical press-fit clearance is 0.1 to 0.2mm, though this varies by printer calibration and filament. Print a test fit before committing to a final assembly.

Heat-set threaded inserts are the professional solution for FDM parts that need to be assembled and disassembled repeatedly. Press a brass insert into a slightly undersized hole using a soldering iron set to around 200 degrees Celsius. The insert melts in, cools, and gives you a proper metal thread that won't strip out the way printed plastic threads do.

Finishing Assembled Pieces Seamlessly

Glue the parts, let the adhesive cure fully, then address the seam. Fill the joint line with spot putty for a smooth result, or pack it with a mixture of CA glue and baking soda for a fast, sandable fill. Let it cure, sand it flush starting at 120 grit and working up, then prime and paint the entire assembled piece as a unit.

"A well-assembled multi-part print should look like it was printed as one piece. The seam is the enemy, and filler is your weapon."

Priming after assembly is the key step. Primer reveals any remaining seam imperfections, gives you one more chance to fill and sand, and then unifies the surface so the paint coat reads as one continuous object.

Post-Processing for Functional Prints

Not every print needs to look beautiful. Some prints need to hold a bracket to a wall, survive vibration inside an enclosure, or thread onto a bolt. For those parts, the post-processing priorities are completely different.

When Aesthetics Take a Back Seat to Function

Decorative prints succeed when they look good. Functional prints succeed when they work correctly under real conditions. That means focusing on dimensional accuracy, structural integrity, and fit rather than surface finish or paint.

Resin functional parts need a full post-cure before use. Under-cured resin is brittle and slightly flexible in ways that cause unexpected failures. Cure completely and consider ABS-like resin formulations for parts that will see impact or repeated stress. These resins are specifically engineered for toughness rather than fine detail.

For FDM functional parts, the FlashForge Inventor with PETG or PLA+ is well-suited to brackets, mounts, and enclosures that need light sanding and hardware inserts. PETG in particular handles heat and mild chemical exposure better than standard PLA.

Thread Tapping, Drilling, and Machining Printed Parts

Thread tapping is the cleanest way to add threaded holes to printed parts. Print the hole slightly undersized, then use a standard tap to cut clean threads. The result is far stronger than printed threads, which tend to strip under repeated use.

Drilling cleans up or enlarges printed holes that came out slightly off. Use sharp bits, run at low speed, and apply minimal pressure. Going too fast generates heat that melts the plastic and grabs the bit. Go slow and let the drill do the work.

Sanding mating surfaces matters for functional assemblies. Two parts that need to sit flat against each other won't seal or align correctly if the surfaces are rough from layer lines. A few passes on a flat sanding block fixes this quickly and improves the fit dramatically.

Lubricate moving printed joints with PTFE lubricant or white lithium grease. A small amount reduces wear and extends the life of the joint significantly.

Your Post-Processing Checklist: From Raw Print to Finished Piece

Post-processing is easier to remember as a sequence than as a set of rules. Run through the checklist in order and you won't skip a step.

Resin Print Workflow Checklist

FDM Print Workflow Checklist

Keep a short post-processing log for each filament or resin you use. Note what sanding grits worked, how long the cure took, and what primer adhered best. Your fifth print of a given material will go much faster than your first because you won't be guessing. Photograph prints before and after post-processing. The improvement will be obvious, and seeing it clearly is genuinely motivating. Not every print needs the full treatment, either. A functional bracket that lives inside an enclosure doesn't need primer or paint. Match the workflow to the purpose.

What's Next: Community, Sharing, and Where to Go From Here

Sharing Your Finished Prints

Post your finished pieces. The reaction from a community of people who understand exactly how much work went into a clean finish is different from showing a photo to someone who's never held a print. It's specific, enthusiastic, and useful.

Reddit is the most active general-purpose community. r/3Dprinting and r/resinprinting both have large, knowledgeable audiences. Instagram rewards well-lit photography and builds a following over time. Printables and Thingiverse let you share the model files alongside finished photos, which creates a record of your work that others can build on. Every post invites feedback, and feedback compresses the learning curve in ways that solo practice doesn't.

The first wash-and-cure you did was probably clumsy. The tenth will feel automatic. That's how this goes.

Preview of Part 10: Community and Ecosystem

Part 8 covered supports and bed adhesion. Part 9 gave you the full post-processing toolkit. Part 10 goes wider: where to find communities, the best model repositories, forums worth bookmarking, and the Discord groups where experienced printers answer questions in real time. The machine is only part of the hobby. The people around it are what make it last.