Beyond print: Finishing techniqu...
Introduction
The world of commemorative and collectible tokens has been revolutionized by additive manufacturing. offer unparalleled design freedom, allowing for intricate geometries, personalized logos, and complex reliefs that would be prohibitively expensive or impossible with traditional minting methods like creating . However, straight off the printer, a 3D-printed coin often reveals its layered origins—visible print lines, support marks, and a matte, plastic-like finish that lacks the heft and prestige of its metal counterparts. This is where the true artistry begins. Post-processing is not merely an optional step; it is the critical bridge between a raw print and a professional-grade collectible. It enhances not only the coin's visual appeal, giving it a polished, high-end look, but also its durability, protecting the surface from wear and tear. This article will cover a comprehensive range of post-processing techniques, from foundational cleaning to advanced finishing methods, that can be used to refine , transforming them from simple plastic discs into stunning, tactile works of art that rival the appearance of traditional and .
Removing Support Structures and Rafts
The first, and often most delicate, step in post-processing is the removal of support structures and rafts. These are essential during printing to prevent overhangs from collapsing, but they leave behind blemishes that must be addressed. The technique for removal depends heavily on the support material and the coin's base material. For common materials like PLA or ABS printed with breakaway supports, manual removal is standard. Using a set of precision needle-nose pliers, flush cutters, or a hobby knife, carefully snap away the supports. The key is to work slowly and methodically, applying pressure at the interface between the support and the coin's surface to minimize stress on the delicate printed details. For more complex geometries or soluble supports (like PVA used with PLA in a dual-extruder setup), chemical removal is a cleaner option. Simply submerging the coin in warm water will dissolve PVA supports over several hours, leaving a much cleaner surface with fewer tool marks. enamel coins
Regardless of the removal method, support "nubs" or scars will almost always remain. This is where initial sanding comes in. Start with a medium-grit sandpaper (around 220-320 grit) to carefully level these protrusions flush with the coin's surface. Use a light touch and sand in small, circular motions to avoid creating deep scratches or altering the intended contours of the design. For hard-to-reach undercuts or intricate text, consider using silicone sanding sticks or needle files. This stage is less about achieving a perfect finish and more about creating a uniform, scar-free canvas for the subsequent smoothing and finishing stages. Patience here prevents having to correct deeper imperfections later.
Sanding and Smoothing
Once supports are removed, the next mission is to eradicate the layered "stair-stepping" effect inherent to FDM 3D printing. This is achieved through systematic sanding. Understanding the difference between wet and dry sanding is crucial. Dry sanding is faster for material removal but generates dust (wear a mask!) and can clog sandpaper quickly. Wet sanding, using waterproof sandpaper dipped in water, keeps the surface and paper cleaner, reduces dust, and provides a smoother finish as the water acts as a lubricant. It is generally preferred for finer grits when working towards a polished surface.
The process follows a strict grit progression. Begin with a coarse grit (e.g., 220) to tackle major layer lines and the remnants of support marks. Once the surface is uniformly textured, move to a medium grit (400-600), then a fine grit (800-1000), and finally, ultra-fine grits (1500-2000+). Each successive grit removes the scratches left by the previous one. Sand in consistent, cross-hatch patterns to ensure even material removal. For coins with deep recesses meant to hold color (like the cells in ), be extra cautious not to sand away the dividing walls (cloisons).
Despite careful sanding, small pits, layer gaps, or printing artifacts may persist. This is where smoothing compounds come into play. Automotive fillers like Bondo spot putty or specialized 3D printing fillers (e.g., XTC-3D) can be applied with a spreader or brush. They fill imperfections and can even help seal porous prints. After application and curing, the surface must be sanded again, starting with a medium grit, to blend the filler seamlessly with the surrounding plastic. This step is invaluable for achieving the flawless, monolithic appearance of a die struck coin .
Painting and Finishing
With a perfectly smooth substrate, the coin is ready for color and protection. Priming is non-negotiable. A high-quality spray primer (filler-primer works excellently) creates a uniform, slightly textured surface that dramatically improves paint adhesion and prevents the plastic's color from bleeding through. Apply 2-3 light, even coats from about 30cm away, allowing proper drying time between coats.
Choosing the right paint depends on the desired effect. Acrylics are user-friendly, water-based, and quick-drying, ideal for hand-painting details. Enamel paints, known for their hard, glossy finish and rich colors, are a classic choice for model painting and mimic the look of traditional . Spray paints offer speed and an ultra-smooth base coat. Advanced techniques bring the design to life: layering thin glazes to build depth, dry-brushing highlights over raised details, and using masking tape or liquid mask to create crisp, multi-color sections. According to a 2023 survey of Hong Kong-based miniature painting and model-making communities, over 65% of artisans prefer a hybrid approach, using spray cans for base coats and high-quality acrylics or -inspired paints for detailed hand-work.
The final protective step is sealing. A clear topcoat locks in the paint job and provides durability. For a matte or satin military-style finish, use a matte varnish. For a glossy, lacquered look reminiscent of premium collectibles, a high-gloss polyurethane or acrylic clear coat is applied. Multiple thin layers are better than one thick layer to avoid runs or cloudiness.
Adding Metallic Accents
To elevate a custom 3D printed coin to truly mimic the feel of metal, incorporating metallic elements is key. The simplest method is using metallic paints. High-quality acrylic metallics or dedicated enamel metallic paints can be brushed or airbrushed onto raised areas for highlights. For a more realistic, burnished metal effect, rub-on metallic waxes or powders (like Rub 'n Buff) are exceptional. Apply a small amount with a fingertip or soft cloth and buff it onto the high points of the design; it adheres to the primer or paint, leaving a convincing, lustrous metal deposit. custom 3d printed coins
For the ultimate in metallic realism, the cold casting technique is unparalleled. This involves mixing fine metal powder (bronze, brass, aluminum) into a two-part epoxy resin or polyurethane casting resin before pouring it into a mold. However, for post-processing a printed coin, a modified approach can be used: create a slurry of metal powder and a thin binding resin or even clear paint, and apply it as a thick coating to the coin's surface. Once cured and polished, it yields a solid metal-like finish that has substantial weight and cool-to-the-touch sensation, closely approximating a die struck coin . The Hong Kong maker scene has seen a 40% increase in the use of cold casting powders for premium in the last two years, driven by demand for heirloom-quality pieces.
Polishing
Polishing is the process of refining a surface to a mirror-like shine, typically performed on already smooth surfaces or after metallic coating. If the coin has been painted with a glossy clear coat, polishing can further enhance its depth and clarity. For bare, sanded plastic or cold-cast metal surfaces, polishing is essential. Start with a coarse polishing compound (often labeled as "cutting" or "rubbing" compound) applied with a soft cloth or a low-speed polishing wheel attached to a rotary tool. This compound removes micro-scratches from the finest sanding stage.
After wiping away the residue, progress to a fine polishing compound ("finishing" or "polishing" compound). Finally, for a showroom-quality, high-gloss finish, a ultra-fine glaze or plastic polish can be used. Each stage uses a cleaner, softer cloth to avoid cross-contamination. The table below outlines a typical polishing progression for a PLA coin coated with a high-gloss clear resin:
| Stage | Compound Type | Application Tool | Purpose |
|---|---|---|---|
| 1 | Cutting Compound (Medium Abrasive) | Foam polishing pad (wheel) | Remove 2000-grit sanding marks |
| 2 | Finishing Compound (Fine Abrasive) | Soft microfiber cloth | Bring up initial shine, remove haze |
| 3 | Plastic/Resin Glaze (Non-abrasive) | Ultra-soft finishing cloth | Achieve final high-gloss, depth |
Epoxy Coating (Optional)
For a dramatic, durable, and glass-like finish, applying a clear epoxy resin coating is a superb option. This technique, often used for high-end bar tops and river tables, creates a thick, dimensional, and incredibly tough protective layer. For challenge coins, it encapsulates the entire design, giving incredible depth to colors and making metallic accents gleam. The process involves mixing a two-part epoxy resin according to the manufacturer's instructions, then carefully pouring or brushing it over the leveled coin. Using a heat gun or torch briefly helps pop surface bubbles. The resin self-levels, creating a perfectly smooth, high-gloss surface as it cures over 24-48 hours.
This method also opens creative possibilities for embedding objects within the coin—tiny LEDs, glitter, dried flowers, or even smaller printed insignias can be suspended in the resin layer. It's important to note that epoxy adds significant thickness and weight, fundamentally changing the coin's profile. While a die struck coin derives its authority from solid metal, an epoxy-coated 3D printed coin gains its presence from a pristine, jewel-like clarity. This technique represents the pinnacle of post-processing, transforming the piece into a unique art object.
Final Thoughts
The journey from a raw 3D print to a refined challenge coin is a testament to the synergy between digital fabrication and traditional craftsmanship. We have explored a comprehensive pathway: starting with the careful removal of supports, progressing through meticulous sanding and filling, applying color and metallic accents with precision, and culminating in polishing or epoxy coating for protection and brilliance. Each technique builds upon the last, and the importance of patience and attention to detail cannot be overstated—rushing any step will be evident in the final result. While carry the weight of tradition and showcase vibrant, cloisonné artistry, offer a new frontier limited only by imagination and finishing skill. We encourage you to view these techniques not as a rigid checklist, but as a toolkit. Experiment, combine methods, and discover the unique processes that allow you to achieve your desired results, creating personalized tokens that are truly beyond the print. die struck coins