Additive manufacturing offers a world of design freedom - but only if you design for it. Far too often, parts that were originally designed for molding or machining are simply sent to a 3D printer, leading to distorted builds, excessive support structures, poor physical performance, and wasted material.
Design for Additive Manufacturing, or DFAM for short, requires a different mindset. Creating a part layer-by-layer changes the game around geometry, material behavior, and secondary operations. Today, we're going to dive into DFAM and explore the details that you should consider before 3D printing a part in FDM (Fused Deposition Modeling).
Let's get started with the basics. What is DFAM? DFAM is a design methodology that outlines the different considerations taken when designing a part for a specific additive manufacturing technology, as opposed to a traditional, subtractive manufacturing process. Some general design considerations to account for are:
1) Material: Different 3D printing materials can vary widely regarding surface finish and printability. What material are you using? Does it have any unique characteristics?
2) Infill: Will your part be printed 100% solid? Or can the part's interior be designed to reduce material and printing time?
3) Sectioning vs Assembling: Large parts may not fit inside the available build volume. Can the part be sectioned, or "cut" into multiple pieces and printed, or should it be designed as multiple pieces and assembled later?
4) Functionality: What is the part being used for? Can some features, such as handles, grips, and sockets be integrated into the parts design?
We'll start with an easy one: wall thickness. It's important to remember that 3D printing works by adding layers of material. That material, often referred to as 'filament' when using FDM technology, is melted and extruded through a nozzle. Subsequently, that line of deposited filament has some width, also known as the toolpath width. FDM 3D printers can do fine details, but walls and other features must be thick enough for the nozzle to lay down at least 2 lines of material. As a general rule of thumb, any wall thickness should be at least twice the thickness of the toolpath. For example, if the toolpath width of the extruder nozzle is 0.020" (0.508mm), the minimum wall thickness it can print is 0.040" (1.016mm), as shown in the image below.
The next most common DFAM consideration is adding fillets and chamfers. In the majority of cases, sharp, 90-degree corners create weak points in a part's geometry, leading to a higher chance of failure when the part is used. To mitigate this, a chamfer or fillet can be added to the corner. When stress is applied to the part, it is distributed more evenly over the radius of the fillet or length of the chamfer, rather than concentrating at the vertex of the corner, as seen in the illustration below.
A frequently used phrase in additive manufacturing is "self-supporting". This refers to the any angled surface where each layer is completely supported by the layer beneath it, thus eliminating the need for support structures. For example, a perfectly vertical wall would be considered self-supporting, as each layer is fully supported by the previous layer. 45 degrees is commonly used as the cut-off point where structures are no longer self-supporting. In other words, a wall that is 30 degrees from the horizontal axis would require a support structure, but a wall that is 60 degrees from the horizontal axis would not. The exact cut-off point will vary based on what machine and material you are using, so be sure to double check!
In the graphic above, we can see 3 types of angles. The blue rectangles represent the cross section of a 3D printed layer. The first, 90 degrees, represents a fully self-supported angle. This is essentially a completely vertical feature. The second, ~45 degrees, represents an angle that is right on the edge of being self-supporting. This wall or feature may or may not require support structures depending on the machine and material used. The third, ~30 degrees, represents an angle that is not self-supporting at all. This feature would likely require support structures (shown by red rectangles), regardless of the machine or material used.
One major advantage of additive manufacturing is the ability to fabricate assemblies with all the parts in place. An excellent example of this is a pre-assembled gear system. To do this, we need to account for adequate clearance. As a minimum guideline, any clearance along the Z axis should the equivalent to the height of one slice. For example, if the slice height of your print is 0.010" (0.254mm), the minimum clearance for parts stacked on top of each other would also be 0.010" (0.254mm). Clearance in the XY plane should be a minimum of 0.008" (0.2mm). Of course, specific applications may allow for tighter clearances or require larger ones, and this can easily be iterated with 3D printing to find the ideal clearance amount. These minimum clearances are shown in the visual below.
Lastly, we need to consider the use of internal cavities. While hollowing out a part in an effort to lighten it or reduce material usage sounds like a good idea, it must be done so carefully. Internal cavities will be filled with support material, unless they are designed in a self-supporting manner. Once printing is complete, we need a way to remove that support material. If you are using soluble support, opening to the internal cavity must be designed into the part to allow the cleaning solution to circulate. If break-away support is used, those opening must be made bigger to allow tools such as pliers, tweezers, or picks to remove the support material.
The illustration above shows a very basic solution to removing support material from an internal cavity. If your design allows for it, add a small hole to allow cleaning solution to enter the cavity when using soluble support. Internal breakaway support requires larger openings or, better yet, geometry that does not require any internal supports.
Designing for additive manufacturing isn’t about following a rigid rulebook—it’s about understanding how the process works and using it to your advantage. When DFAM principles are applied thoughtfully, 3D printing becomes more than a prototyping tool; it becomes a powerful manufacturing solution capable of producing strong, efficient, and highly integrated parts.
By considering factors such as wall thickness, self-supporting geometry, clearances, and internal features early in the design phase, you can minimize print failures, reduce post-processing, and significantly improve part performance. Most importantly, DFAM encourages designers to rethink traditional constraints and embrace the unique capabilities of layer-by-layer fabrication.
As additive manufacturing continues to evolve, the most successful parts won’t be the ones that simply can be printed—but the ones that were designed to be printed. Taking the time to design with the process in mind will save time, material, and frustration, while unlocking the full potential of FDM 3D printing.