The world of challenge coins, once dominated by traditional manufacturing methods like and intricate , has been revolutionized by the advent of 3D printing. offer unparalleled flexibility in design, allowing for complex geometries, personalized text, and rapid prototyping that traditional methods cannot match. From commemorative pieces for corporate events to unique tokens for gaming communities, 3D printing empowers creators to bring their visions to life with relative ease and affordability. However, this convenience comes with its own set of challenges. The layer-by-layer additive process is sensitive to a myriad of factors, and what looks perfect in a digital model can sometimes manifest as a flawed physical object. This article will address the most common problems encountered when 3D printing challenge coins and provide practical, step-by-step solutions to help you achieve the high-quality finish your designs deserve. By understanding these issues, you can bridge the gap between the digital precision of your design and the tangible reality of a flawless coin.
A successful 3D print begins with a perfect first layer. For the fine details and often small footprint of challenge coins, bed adhesion is paramount. Two primary issues plague this initial stage: warping and the first layer not sticking.
Warping occurs when the corners or edges of your print lift away from the print bed during the printing process. This is caused by uneven cooling and material contraction. As the molten plastic from the nozzle cools and solidifies, it shrinks slightly. If the adhesion to the bed is not strong enough, this internal stress pulls the edges upward, ruining the coin's flatness and dimensional accuracy. Common causes include an unheated or inadequately heated print bed, drafts in the printing environment, and a bed surface that lacks proper grip.
Solutions are straightforward but crucial. First, ensure you are using a heated bed. For materials like PLA, a temperature of 50-60°C is often sufficient, while ABS may require 90-110°C. Applying a thin layer of adhesive, such as a glue stick, hairspray, or a dedicated 3D printing adhesive, significantly improves grip. For small, detailed items like coins, using a "brim"—a single-layer flat area extending from the object's outline—provides extra surface area for adhesion and is easily removed post-print. In severe cases, a "raft" (a thick, disposable foundation) can be used. Finally, enclosing your printer helps maintain a consistent ambient temperature, eliminating drafts that cause uneven cooling. This is especially important when aiming for the precision required for , where even minor warping can distort fine lettering or emblems.
If the filament simply doesn't adhere to the bed and gets dragged around by the nozzle, the print fails immediately. This is often due to an incorrect nozzle height (the "Z-offset"). If the nozzle is too high, the filament is laid down in the air and doesn't press into the bed; if it's too low, it can scrape the bed and block extrusion. A dirty print bed covered in oils from your fingers or leftover adhesive from previous prints is another common culprit. An insufficient bed temperature can also prevent the plastic from staying soft long enough to bond.
To solve this, start with a meticulous bed leveling procedure. Modern printers often have assisted leveling, but manual paper-leveling remains a reliable method. The goal is to have a slight friction between the nozzle and a piece of paper at all points on the bed. Next, clean the print surface thoroughly with isopropyl alcohol (IPA) before every print to remove any contaminants. If problems persist, fine-tune the nozzle height in your printer's settings during the first layer. A well-adhered first layer should be slightly squished, with adjacent lines merging together without gaps. Ensuring this foundational step is correct is more critical for a 3D printed coin than for a large, simple print, as the entire detail rests upon it.
Once the print is anchored, the next battle is achieving clean, sharp details without unwanted artifacts. Stringing and blobs are the enemies of a coin's crisp features and smooth surfaces.
Stringing, or "oozing," appears as thin wisps of plastic stretched between separate parts of the print, like across the open center of a coin or between raised letters. It happens when molten filament drips from the nozzle during non-printing travel moves. The primary causes are insufficient retraction settings, a printing temperature that is too high (making the filament too runny), and travel moves that are too slow, giving the filament more time to ooze.
Combating stringing requires tuning your slicer settings. Retraction is the key setting: it pulls the filament back slightly when the nozzle moves to a new location, creating a negative pressure to prevent dripping. Increase the retraction distance (typically 2-6mm for direct drive extruders, 4-8mm for Bowden) and speed. Lowering the printing temperature by 5-10°C can dramatically reduce oozing without compromising layer adhesion. Finally, increasing the travel speed ensures the nozzle moves quickly between points, minimizing time for filament to leak. For a challenge coin with intricate separations, perfecting these settings is essential to avoid a web of plastic that obscures the design, a flaw never seen in precision .
Blobs and zits are small, protruding bumps on the surface of the print, often found at the start or end points of a perimeter. They are caused by inconsistent extrusion, often due to moisture in the filament that turns to steam and pops, or by poor management of the layer seam—the point where each outer layer begins and ends.
Start by ensuring your filament is dry. Many plastics, especially PLA and nylon, are hygroscopic. In humid climates like Hong Kong, where average relative humidity can exceed 80% for much of the year, filament can absorb enough moisture from the air in a matter of days to cause printing issues. Use a filament dryer or a food dehydrator to remove moisture before printing. Next, calibrate your extruder's E-steps to ensure it's pushing the exact amount of filament commanded. Finally, address the seam. In your slicer, you can choose to align the seam to a specific corner (less visible on sharp edges), set it to "random" (scattering the blobs, making them less noticeable), or use "sharpest corner" hiding. For a coin meant to be a smooth, display-worthy object akin to an enamel coin , managing these surface blemishes is critical.
The infill inside your coin provides structural integrity without using solid material. Problems here can lead to weak coins or visible internal patterns on the surface.
A coin that feels brittle or flexes easily likely suffers from weak infill. This is typically due to a low infill percentage (e.g., below 15% for a small object), an inefficient infill pattern, or a printing temperature that is too low, preventing proper layer bonding.
For a small, dense object like a challenge coin, a higher infill density is recommended—often 25% to 40%—to ensure it has a substantial feel. The choice of pattern matters greatly. While grid is common, patterns like "gyroid" or "honeycomb" offer excellent strength-to-material ratios and more uniform internal support. Increasing the printing temperature within the filament's recommended range can improve the melting and bonding of the infill strands, making the internal structure much stronger. A robust infill is what allows a custom 3D printed coin to have the heft and durability that approaches, even if doesn't fully match, the solid feel of a metal die struck coin .
If the infill pattern is not properly bonded to the outer walls (perimeters), it creates a weak point where the shell can separate from the core. This is often visible as gaps between the solid outer wall and the infill pattern when examining a broken print. Causes include a printing temperature that is too low for good layer adhesion and an insufficient "Infill Overlap" setting in the slicer.
The solution is to increase the printing temperature slightly to ensure the infill material is molten enough to fuse with the already-printed wall. More importantly, adjust the "Infill Overlap Percentage" setting. This controls how much the infill pattern extends into the wall area. Increasing this value from a default of 15% to 25-30% ensures a strong mechanical bond between the infill and the perimeters, creating a unified, solid object. This is crucial for coins that may have thin sections or intricate cut-outs.
For a challenge coin, size matters. Whether it needs to fit a standard holder or match a specific diameter, dimensional inaccuracies can render it useless.
If your printed coin consistently measures differently from your CAD model, the issue is systemic. Causes include incorrect calibration of the printer's motion system (steps per millimeter for X, Y, and Z axes), incorrect scaling factors in the slicer software, and material-specific shrinkage as the plastic cools.
Begin by calibrating your printer's steps per millimeter (steps/mm). Print a simple 20mm calibration cube and measure it with digital calipers. Use the formula: New Steps/mm = (Current Steps/mm * Expected Dimension) / Measured Dimension. Apply this correction for each axis. Ensure your slicer is not applying any unintended scaling (it should be at 100%). Finally, account for shrinkage. Materials like ABS can shrink by up to 0.8%. If precision is paramount, you may need to scale your model up slightly (e.g., 100.5% to 100.8%) in the slicer to compensate. This level of calibration is what separates a hobbyist print from a precision-made token.
Small holes for keychains or intricate design features on the coin appearing oval or misshapen point to mechanical issues. The primary culprits are loose belts on the X and Y axes, which cause slop and inaccuracy in movement, and backlash in the motion system. Additionally, using a layer height that is too large can create a "stair-stepping" effect on curved surfaces, making circles appear polygonal. enamel coins
Tighten the printer's belts so they twang like a guitar string when plucked, but are not overtightened. Check for any play or wobble in the carriages and tighten eccentric nuts as needed. To improve the roundness of holes and curves, reduce your layer height. Printing at 0.1mm or 0.08mm layer height will produce much smoother curves than 0.2mm, though it will increase print time. For a challenge coin, where aesthetic perfection is often the goal, this trade-off is usually worth it to achieve details that rival the sharpness of .
The final appearance of your coin is what makes it presentation-ready. Layer lines and elephant's foot can detract from an otherwise perfect print.
Visible, pronounced layer lines are the most common hallmark of an FDM 3D print. While some finishing can reduce them, preventing severe lines is best. Causes include using a large layer height, inconsistent extrusion leading to over- or under-extrusion bands, and mechanical vibrations or wobble in the printer frame.
To achieve a smoother surface suitable for a display coin, reduce the layer height. As mentioned, 0.1mm is a good target. Ensure your extruder is perfectly calibrated to provide consistent flow. Stabilize your printer by placing it on a solid, heavy surface or a vibration-dampening pad. For the ultimate finish, consider post-processing: light sanding, priming, and painting can create a surface that mimics the smooth, colored finish of . Some creators in Hong Kong's maker communities even use centrifugal polishing machines with fine media to achieve a near-professional sheen on their .
Elephant's foot is a slight bulge or flare at the very bottom of the print, where the first few layers are wider than intended. This can prevent coins from sitting flat or distort the lowest details. It is caused by the first layer being squished too much into the bed (often from a slightly too-low nozzle) and/or an excessive bed temperature that keeps the bottom layers soft and allows them to sag under the weight of the layers above.
The primary fix is to adjust your first layer settings. You can slightly increase the "Initial Layer Horizontal Expansion" setting in your slicer (a negative value of -0.1mm to -0.2mm) to compensate for the bulge by shrinking the first layer's dimensions. Alternatively, ensure your nozzle height is perfectly calibrated to avoid excessive squish. Lowering the bed temperature after the first few layers can also help. For a coin that needs a perfectly vertical edge, eliminating elephant's foot is a necessary step in pre-processing.
The quality and condition of your filament are fundamental. Two critical failures stem from the material itself: snapping and clogging. custom 3d printed coins
If the filament breaks in the extruder or feeder, the print will fail due to under-extrusion. This is common with old PLA that has become brittle from moisture absorption. A filament path with tight bends or excessive friction can also cause it to snap under tension. die struck coins
Always use fresh, well-stored filament. In humid environments, store filament in sealed bags with desiccant. If filament becomes brittle, drying it in a dedicated dryer or a low-temperature oven (around 45-50°C for PLA) for several hours can restore some flexibility. Optimize the filament path from the spool to the extruder, ensuring there are no sharp bends and that the spool can rotate freely. A local survey of Hong Kong-based 3D printing enthusiasts in 2023 indicated that filament moisture issues were the second most common cause of print failures, highlighting the importance of proper storage.
A clogged nozzle leads to under-extrusion, eventually stopping extrusion entirely. Causes include debris (carbonized plastic, dust) in the nozzle, printing at too high a temperature for prolonged periods (causing heat creep and filament expansion before the melt zone), and overly aggressive retraction settings that pull molten filament too far up into the cooler heat break, where it solidifies.
Regular maintenance is key. Perform "cold pulls" or "atomic pulls" to clean the nozzle: heat the nozzle, insert filament, cool it down to just above the glass transition temperature, and then pull it out sharply, which should bring contaminants with it. Lower your printing temperature to the lower end of the filament's recommended range if you are experiencing heat creep. Review your retraction settings; excessive retraction distance is a common cause of clogs in Bowden setups. Ensuring a clean, well-tuned extrusion system is the final piece of the puzzle for reliably producing high-quality coins.
3D printing challenge coins is a journey of balancing creativity with technical precision. From ensuring the first layer sticks perfectly to eliminating stringing and achieving dimensional accuracy, each challenge has a logical solution rooted in understanding the process. While a custom 3D printed coin may not have the instant, flawless finish of a factory-produced die struck coin or the glossy depth of , the ability to iterate, personalize, and produce in-house is its superpower. Do not be discouraged by failed prints; each one is a learning opportunity that deepens your understanding of your machine and materials. The 3D printing community, including vibrant forums and local maker spaces in cities like Hong Kong, is an invaluable resource for shared knowledge and troubleshooting. With patience and practice, you can consistently produce challenge coins that are not only meaningful in design but also impeccable in execution.
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