Chloe Zhang
3D printing plastic gears is a cheap, quick, and customizable motion transfer solution. While the process is quick and clean, it is important to note that commonly available plastics may not offer the same level of surface finish and durability as injection-molded or machined plastic parts. However, when designed correctly, 3D-printed gears can efficiently handle reasonably high load transfers and are ideal for specific applications, such as speed reducers for small electric motors or hand cranks. The choice of plastic material is crucial, with options like nylon, PLA, PETG, and ABS, each offering unique advantages and considerations. Post-processing is often required to refine details like bore holes and gear teeth.
| Characteristics | Values |
|---|---|
| Advantages of 3D printing gears | Cheap, quick, customizable, ideal for prototyping, accessible |
| Disadvantages of 3D printing gears | Sacrifice in surface finish and durability |
| Common issues | Centre hole shrinkage, undersized holes, rubbing instead of rolling |
| Materials | Nylon, PLA, PETG, Delrin (POM), ABS, Polycarb |
| Techniques | FDM, 3D printing metal parts, pressure extrusion |
| Post-processing | Bore holes, clean up teeth with a blade, gear hob style file, cutter |
| Angle | 25 degrees for balance of chunkiness and motion transfer |
| Thickness | At least three to five times the circular pitch of the gear |
| Strengthening techniques | Add a solid wall, reduce unsupported area, press fit on knurled shaft |
| Set screw techniques | Thread into plastic, trap nut inside gear, recessed hex |
| Lubricant | Graphite, 3-in-1 oil, lithium grease |
| Temperature resistance | 94 degrees C |
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What You'll Learn
Choosing the right plastic
When choosing the right plastic for 3D printing gears, there are several factors to consider, including the desired strength, temperature performance, impact strength, and lubrication requirements. Here are the key points to help you select the most suitable plastic for your needs:
Firstly, nylon is widely regarded as the best choice for 3D printing gears due to its exceptional strength, resistance to high temperatures, and low friction coefficient. Nylon gears also benefit from high inter-layer adhesion, resulting in solid parts with no flaws, and they do not require additional lubrication. These factors make nylon an excellent option for applications requiring high strength and durability.
Polylactic Acid (PLA), a plant-based plastic, is another popular choice for 3D printing gears. It offers good stiffness and strength, resulting in strong and reliable gears. However, one of its limitations is its inability to withstand high temperatures; PLA gears tend to deform at temperatures between 45°C and 50°C. Therefore, if your application involves high temperatures, PLA may not be the best choice.
Acrylonitrile Butadiene Styrene (ABS) is also worth considering due to its impact strength and durability. ABS gears will generally last longer than those made from PLA. Additionally, ABS is derived from petrochemicals, so it is compatible with oil-based lubricants, which can enhance its performance in certain applications.
Polyethylene Terephthalate (PETG) stands out for its low-temperature performance. If your application involves low temperatures, PETG could be a suitable choice. However, it is important to note that PETG is quite elastic, which may be a disadvantage for gear applications.
Finally, consider the lubrication requirements for your gears. While nylon gears typically do not require lubrication, other plastics like PLA, PETG, and ABS may benefit from lubrication to reduce friction and wear, especially in high-stress environments. White lithium, PTFE, and silicone-based lubricants are recommended for these plastics and are suitable for general use.
In summary, the choice of plastic depends on the specific requirements of your application. Nylon is the top choice for its strength and temperature resistance, followed by PLA and ABS, which offer good strength and durability. PETG excels in low-temperature performance but may be too elastic for some gear applications. Remember to consider lubrication for certain plastics to enhance their performance and prolong their lifespan.
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Post-processing techniques
Post-processing is critical in 3D printing as it improves the overall quality, appearance, and functionality of printed objects. Here are some common post-processing techniques for 3D printed plastic gears:
Sanding
Sanding is a process of smoothing out surface roughness and eliminating layer lines and support marks. It is often necessary for models printed via Fused Filament Fabrication (FFF) or Selective Laser Sintering (SLS). Start with coarser grit sandpaper and gradually move to finer grits to achieve a smooth finish. Light sanding or manual sanding can be done, or power tools can be used for more efficiency. Wet sandpaper can also be used to smooth out rough spots and polish the printed part.
Chemical Smoothing
Chemical smoothing is an advanced technique that can improve the surface finish of 3D printed parts, especially those made from ABS plastic. This involves exposing the part to a chemical solvent, such as acetone, which partially dissolves the surface layer, smoothing out layer lines and imperfections. This process can also be done through vapor smoothing, where the printed part is placed in a closed container with the solvent, creating a saturated atmosphere that dissolves the outer layer. It is important to ensure proper ventilation and safety precautions when working with chemicals.
Painting and Coating
Applying paint, varnish, or other coatings can improve the appearance and durability of 3D printed parts. Spray paint or powder coating provides an even and uniform finish, enhancing wear resistance. Brush coating can also be used, especially for unique or small batches, but it may be more difficult to avoid brush strokes. Resin products can be used to achieve very smooth surfaces, and additional coatings can be applied for an even smoother finish.
Foiling or Vinyl Wrapping
Foiling involves wrapping an adhesive foil made of light metals or plastic onto the object, often after priming. This technique can enhance heat and stress resistance and improve surface quality and aesthetics. It is suitable for simple geometries and can add detailed surface designs to 3D-printed parts.
Abrasive Blasting (Sandblasting)
Abrasive blasting is a powerful technique that employs abrasive materials, such as glass beads, sand, or plastic beads, propelled at high pressure to clean and texture the surface of the 3D printed part. It achieves a uniform finish and is effective for smoothing intricate designs and hard-to-reach areas. Sandblasting requires proper ventilation, protective gear, and careful media selection.
Other post-processing techniques that can be used for 3D printed plastic gears include electroplating, tumbling, CNC machining, and support removal. These techniques offer specific benefits and are chosen based on the desired outcome and material used.
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Improving performance
When it comes to improving the performance of 3D-printed plastic gears, there are several factors to consider. Firstly, the choice of material is crucial. While nylon is often recommended for its durability and self-lubricating properties, it requires precise printing conditions. Other options include PLA, which is easy to print and dimensionally accurate but not suitable for high-temperature or high-load applications, and ABS, which offers better impact resistance than PLA but needs careful printing conditions. For a balance between strength and flexibility, PETG is a suitable choice for medium-duty gears.
To enhance the strength of the gear teeth, consider increasing the thickness of the gear. Additionally, a solid wall over the face of the gear teeth can reduce their unsupported area, improving their strength. The number of teeth on a gear is also important, as it affects gear ratio, torque, speed, smoothness, durability, and noise levels. Gears with more teeth tend to provide smoother rotation and reduce backlash.
Optimising print settings is another way to improve performance. A lower layer height improves detail and gear meshing but increases print time. A higher infill density, such as 50-70%, is recommended for strength, while 100% infill may be necessary for high-load applications. Printing gears flat on the bed reduces layer delamination and enhances strength, and a slower print speed improves precision. To prevent overheating and minimise distortions, use proper cooling settings and a heated bed.
Post-processing techniques can also improve the performance of 3D-printed plastic gears. Centre hole shrinkage is a common issue, and it may be necessary to bore holes to the right size and clean up teeth with a blade. Using a gear hob or an accurate cutter can help refine the teeth, but it is important to keep the gears cool during this process as plastics can heat up under machining, affecting tolerances.
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Pros and cons of 3D printing gears
3D printing gears have various advantages and disadvantages compared to traditional gear manufacturing methods. Here is a detailed list of the pros and cons:
Pros:
- Cost-efficiency: 3D printing gears are cheaper than other gear-making methods. The prototyping and creation process is quick and clean, reducing the amount of time and labour required.
- Customization: 3D printing offers high flexibility and customization potential. There is almost no limit to the designs that can be created, and complex variations are easily achievable.
- Convenience: 3D printers are widely available, and digital gear designs can be easily shared and reproduced by anyone with a 3D printer.
- Uniqueness: 3D printing allows for the creation of unique parts that might not be possible or feasible with traditional manufacturing methods.
- Speed: 3D printing can speed up the production of very complicated parts.
Cons:
- Durability: 3D printed plastic gears may not be as durable as injection-molded or machined plastic parts. The surface finish is often not as refined, and the gears may not be able to withstand high loads or temperatures.
- Post-processing: 3D printed gears usually require additional work, such as boring holes and cleaning up teeth with a blade, before they can be used.
- Precision: 3D printing technologies may not be advanced enough for precision manufacturing, especially for small gears where even minor tolerance issues can be magnified.
- Material limitations: While nylon is commonly used for 3D printed gears, it may not be suitable for all applications. Other materials, such as PLA, PETG, and metal, have their own advantages and disadvantages, but the availability of suitable materials for 3D printing gears is still limited compared to traditional manufacturing.
- Equipment cost: 3D printing equipment can be expensive, and the technology is still evolving, which may make it cost-prohibitive for some.
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Designing and printing considerations
The design process for 3D-printed gears involves several key considerations. Firstly, the choice of materials is crucial. Nylon is widely regarded as the best material for printing gears due to its stiffness, low friction coefficiency, high melting point, and inter-layer adhesion. However, it is important to note that nylon is not waterproof. Other suitable materials include PLA, ABS, and PETG, although PLA has limited resistance to high temperatures, and PETG is quite elastic, which may be a disadvantage for gears.
The angle of the gear teeth is another important factor. A 25-degree angle is recommended for a balance of strength and efficient motion transfer, particularly for palm-sized gears. Increasing the thickness of the gear can also enhance its strength, with a general rule suggesting the thickness should be three to five times the circular pitch. Additionally, increasing the module size can improve accuracy, as most 3D printers have a tolerance of +/- 0.1 mm.
The ratio of the gears is a critical design aspect. The recommended ratio for 3D-printed gears is between 0.2 and 5. This ratio influences the number of teeth on the gear, with higher ratios requiring more teeth. For example, a 2:1 ratio can result in combinations such as 30 and 60, 15 and 30, or 8 and 16. It is important to avoid extreme ratios, as they may hinder successful operation.
When designing the teeth of the gear, it is worth considering that a higher number of teeth can lead to weaker areas or pinch points. Therefore, a lower number of teeth can result in a stronger gear. However, very few teeth can increase the risk of breakage and inaccurate gear operation. Additionally, the precision of the teeth is crucial, as even minor discrepancies can lead to significant issues.
Lastly, centre hole shrinkage is a common issue in 3D printing, even with expensive printers. This issue arises due to thermal contraction of cooling plastic and the modelling of holes as polygons with many segments. To mitigate this, it is recommended to export gear STLs with higher segment counts and be mindful of the potential for misalignment between layers and discrepancies in extrusion width.
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Frequently asked questions
3D printing plastic gears is a cheap, quick, and customizable motion transfer solution.
The best materials to use are nylon, PLA, or PETG. Nylon is the best choice for gears that need a slippery surface, but it is difficult to print with and absorbs water. PLA is a good choice due to its stiffness, but it does not resist high temperatures. PETG is easy to print with, has good heat resistance, and is totally odour-free.
A 25-degree angle is a good balance of chunkiness and efficient motion transfer for a palm-sized gear.
Printed gears usually require some post-processing, such as boring holes to the right size and cleaning up teeth with a blade.
You can secure a set screw by threading it into the plastic gear directly or by trapping a nut inside the gear via a square hole. However, the former method risks stripping the delicate plastic threads, and the latter method can cause the hub to break if not done properly.
