Your Go-To Guide for Designing 3D Models for FDM Printing

Adhere to the appropriate design principles when crafting 3D models for additive manufacturing to prevent print mishaps and substandard parts.

When it comes to 3D printing, mastering the nuances of your craft can make a world of difference. It’s not just about getting the best 3D printer or choosing the right filament; it's about understanding the unique art of designing 3D models specifically for Fused Deposition Modeling (FDM) printing. Today, we're pulling back the curtain on this process, providing you with a handful of tried-and-true tips and tricks that'll supercharge your 3D printing journey.

Understanding FDM 3D Printing

Before diving into the ins and outs of 3D model design, let's clarify what FDM 3D printing is. FDM is a type of additive manufacturing technology where a thermoplastic material is heated and extruded layer by layer to build up a 3D object. The technology is widely used due to its affordability, robust material options, and versatility in making functional prototypes and end-use parts.

Best 3D CAD Modeling Software's 

There are two primary methodologies in 3D computer-aided design (CAD) modeling: parametric and direct modeling. Parametric modeling is a strategy that uses features and constraints to capture design intent in 3D CAD. This method is particularly useful for automating repeated changes typically seen in product part families. Conversely, direct modeling allows you to swiftly define and manipulate geometry, eliminating the need to fret over features, constraints, and the original design intent. It's often likened to sculpting with modeling clay—you simply mold the geometry until it meets your desired shape.

Once you've decided on the modeling style that suits your needs, the next step is to select your 3D modeling software. Here's a rundown of some of the most widely used 3D CAD software options for hobbyists and professionals alike:

Software	Difficulty	Type	Cost
Fusion360	Moderate	Direct and Parametric	Free 30-Day $70 / month
Blender	Moderate	Direct and Parametric	Free and Open Source
Tinkercad	Easy	Parametric	Free
PTC Creo	Hard	Parametric	Starting at $2,780 / year
SolidWorks	Hard	Parametric	Starting at $5,590 / year

Designing for FDM: Key Considerations

Designing for FDM printing requires a tailored approach rather than a one-size-fits-all solution. Here are some critical aspects to contemplate:

1. Layer Height: Layer height is perhaps the most consequential parameter in FDM 3D printing. This selection can notably impact the strength, speed, and resolution of your final printed part. It's recommended to increase the layer height only up to 75 percent of your nozzle diameter. For instance, a nozzle with a 0.4 mm diameter should ideally print at a layer height of 0.3 mm.

2. Wall Line Count: A common misconception among users is to boost the infill percentage to enhance the strength of a part. However, a significant increase in strength can be achieved more effectively by amplifying the wall line count. For end-use parts that are required to endure high loads, we suggest incorporating six or more walls.

3. Overhangs and Support Structures: Navigating overhangs can be a complex part of FDM 3D printing. It's crucial to comprehend how to employ support structures efficiently to offset sagging and maintain the dimensional precision of your print. The rule of thumb is to incorporate support material for overhangs that extend over 45 degrees relative to the print surface. However, the faster your 3D printing speed, the more cooling will be needed for the printed part to adhere to this guideline.

5. Material: The choice of 3D printing filament can yield varying outcomes, even when the design remains constant. It's essential to familiarize yourself with the specific properties of the material, such as its flexibility, strength, and resistance to temperature, prior to selecting the ideal filament for your project.

Top Tips and Tricks for 3D Model Design for FDM

Chamber Overhangs

Adhering to the 45-degree overhang rule can be simplified by integrating as many chambers into your design as possible. These chambers provide even layer stepping that doesn't necessitate support material.

Rounded Corners

Employing a fillet on corners allows for a smoother transition for 3D printers. Given that 3D printers must decelerate and accelerate around sharp corners, this task can be more challenging, especially at high speeds. However, avoid fillets for overhangs as they are more difficult to print compared to chambers.

Segmented Printing Plane

All thermoplastic materials used in FDM 3D printing possess a shrink ratio, causing the filament to contract, particularly at locations with more material. It's best practice to have a generous amount of material for the first layer, but this larger mass can lead to warping from the print surface. To prevent this, segment your first layer. This can be achieved by extruding and cutting material away from the initial few layers.

Removing Top Layer Material

This strategy addresses the common issue of hull lines in 3D printed objects. To ensure a uniform thermal heat transfer when your 3D printer transitions from infill to top layers, cut away material from the top plane. This results in a stair-step pattern in your top layers.

Heat Inserts

The most secure way to assemble 3D printed components is through heat inserts. Design holes slightly smaller than the heat insert and meld the insert into the part with a soldering iron press. Mastering this process can require practice and adaptation to your material. You can purchase heat inserts designed for FDM 3D printed parts here. 

Increased Allowance

An allowance is a deliberate deviation between two mating parts or dimensions in a fit. FDM 3D printing demands a larger allowance for clearance holes compared to traditional manufacturing techniques. For instance, an M3 bolt through-hole should be adjusted to 3.2 mm or more, depending on your 3D printer and speeds.

Sequential Bridging

The sequential bridging technique, introduced by Nophead Afaik in his 2014 blog post "Buried nuts and hanging holes", is worth noting. Most FDM 3D printers can create a bridge with a 90-degree overhang for a short span, less than 10 mm. However, bridges with cut-outs can make bridging impossible. In such cases, like a bore housing a nut, sequential bridging can be used to establish layers of multiple mini-bridges that bypass the hole. This method decreases the need for support material.

 

 

Sequential bridging used to avoid support material for nut housing. (Image credit: Makers Muse)

Topology Optimization

Topology optimization is a mathematical approach that tailors the material arrangement within a designated design space, taking into account specific loads, boundary conditions, and constraints with the objective of enhancing the part's performance. This strategy results in organic geometries, which, though challenging to produce with traditional manufacturing methods, can be readily created with 3D printing. There is undoubtedly a learning curve involved, but most parametric 3D modeling programs offer a topology optimization tool.

Conclusion

Designing 3D models for FDM printing can be an enjoyable and fulfilling experience when you grasp the fundamental principles. With the appropriate software, some practice, and the application of these tips and tricks, you're on the right track. After mastering the art of designing 3D models for printing, you'll be ready to tackle how to make money with your new skill.