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Design Guide: FDM 3D Printing

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Fused deposition modeling (FDM) is one of the most common forms of additive manufacturing (AM). It is ideal for prototyping, modeling and low-volume manufacturing. Unlike other 3D printing processes, such as SLA, SLS and DMLS, that use powder and resin materials, FDM process filament materials. For this reason, it is a unique process to design for.


FDM 3D printing designs


This article offers a comprehensive guide to the best design practices for FDM 3D Printing. It includes an overview and considerations of the process, design guidelines, and a summary of best design practices.


FDM 3D Printing Process

In FDM, a thin polymer-based filament is extruded through a heated nozzle, which melts and deposits material layer by layer to form the final object. The process is compatible with a wide range of filaments, proving material flexibility.


Disadvantages of the FDM Process

  • Coners: Because the nozzles used in FDM are circular, corners and edges have a radius equal to the nozzle size. In other words, these features are never perfectly square.
  • Anisotropic: Due to how FDM printers extrude lines of thermoplastic material one layer at a time, the process is inherently anisotropic — in other words the part’s bulk mechanical properties vary along different directions.
  • Warping: During the cooling process, different sections of the print solidify and shrink at different speeds. This can cause internal stresses and result in the parts warping. Certain FDM design features like vertical walls or thin sections can increase the likelihood of warping to occur.


Characteristics of FDM 3D Printing

Maximum Build Size800 x 800 x 550 mm
Dimensional Accuracy±0.3% (with a lower limit of ±0.3 mm)
Common MaterialsABS, Nylon (PA), PC, PLA, TPU
Surface StructureRough. Visible layer lines



FDM Design Guidelines


Issues with overhangs are one of the most common FDM print-quality problems. Depending on the material, an overhang can usually be printed up to 1.2mm in length and up to 45° without compromising quality. Anything above these limits will require support.


Designing overhang angles for 3D printing


Unsupported Walls

With FDM, unsupported walls—connected to the rest of the print on less than two sides—are at a high risk of warping. To avoid this, they should be at least 1.2mm thick.


Designing unsupported walls for 3D printing


Supported Walls

These walls are connected to other structures on at least two sides (so they have a very low likelihood of warping). Supported walls should be designed with at least 1.0mm thickness.


Designing thickness for supported walls


Pins and Columns

Pins are tall thin features with a circular cross-sectional area. The diameter of a pin can be designed to 0.8mm, but even then, risk breaking. The minimum reliable pin diameter is 1mm.


Designing pin diameter and height in 3D printing designs


Mating Parts

For FDM parts, adequate clearances must be designed between mating parts to prevent the assembly from sticking together. To avoid this, models must be designed with a minimum clearance of 0.5mm.


How to design mating parts in 3D printing


Embossed Details

Embossed features must be designed using a minimum height, otherwise, it will not appear visible. Such features should be designed at least 0.3mm in height.



Engraved Details

Engraved features must be designed using a minimum depth and width, otherwise, it will not appear visible. Engraved details should be at least 0.5mm deep and 0.5mm wide.


How to design engraved text and details


Summary of Best FDM Design Practices

OverhangsUp to 1.2mm in length and up to 45°
Unsupported WallsAt least 1.2mm thick
Supported WallsAt least 1.0mm thick
PinsMinimum reliable diameter is 1.0mm
Mating PartsMinimum clearance of 0.5mm
Embossed DetailsMinimum height of 0.3mm
Engraved DetailsMinimum depth of 0.5mm; minimum width of 0.5mm



Getting Your Parts Printed

Use the 3D Printing Design Guidelines to help design your parts for machining then export your 3D CAD files into an STL format. Once ready, upload your files here to get an instant quote. Please keep in mind that these are general guidelines, and your specific part geometry and manufacturing requirements may vary depending on different factors such as material choice. If you have any questions, you can get contact with us at or through our get in touch form for more information.


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