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When using an FDM 3D printing service, proper design is critical to achieve strong, accurate, and functional parts. FDM has specific design constraints that, if respected, can produce reliable components suitable for both prototyping and end-use applications. When using an FDM 3D printing service, proper design is critical to achieve strong, accurate, and functional parts.
FDM (Fused Deposition Modelling) builds parts layer-by-layer by extruding thermoplastic filament. This additive process introduces unique design considerations compared to subtractive manufacturing or alternative 3D printing technologies like SLA or SLS.
Two of the most critical factors in FDM design are layer adhesion and part orientation. Inadequate design choices in these areas often result in poor inter-layer bonding, dimensional inaccuracies, and extensive post-processing requirements.
Field insight: Many first-time users overlook how orientation affects strength. Layer direction largely determines whether a part can handle tensile or shear forces.
FDM (Fused Deposition Modelling) builds parts layer-by-layer by extruding thermoplastic filament. This additive process introduces unique design considerations compared to subtractive manufacturing or alternative 3D printing technologies like SLA or SLS. A helpful Formlabs guide on FDM design principles also provides additional context for engineers transitioning into additive manufacturing.
Maintain a minimum wall thickness of 1.2 mm for non-load bearing parts. For functional or load-bearing components, 2-3 mm walls are recommended. Thin walls may warp or fail under stress. In high-load applications such as fixtures or brackets, walls of 4 mm or more may be necessary to prevent structural failurre.
Infill supports internal structure without solidifying the entire part. Higher infill percentages significantly increase strength but also extend print time and material usage.
20-40% infill: suitable for visual prototypes or low-stress components.
60-100% infill: appropriate for functional parts requiring load-bearing capacity.
Field insight: Engineers often underestimate infill’s role in part stiffness. Balancing infill with wall thickness yields optimal strength-to-weight ratios.
Sharp corners concentrate mechanical stress. Adding fillets or chamfers to both internal and external edges distributes loads more evenly, reduces crack initiation points, and improves print reliability. Fillets with radii of 2-5 mm are often effective for most FDM parts.
FDM prints holes slightly undersized due to shrinkage and nozzle precision. To compensate, design holes 0.2-0.5 mm larger than the intended diameter. Always account for printer calibration and material-specific behaviour.
Field insight: For highly precise features like dowel pins or press-fit assemblies, secondary machining such as drilling or reaming remains necessary.
FDM printers struggle with overhangs greater than 45 degrees without support structures. Where possible, redesign features to limit unsupported angles. Bridges under 10 mm typically print successfully without drooping, provided cooling is adequate.
Standard layer heights range from 0.1 mm to 0.3 mm:
0.1-0.15 mm: high detail, smooth surface finish, longer print times.
0.2-0.3 mm: faster prints, suitable for prototypes and functional parts.
Nozzle diameter (typically 0.4 mm) dictates minimum feature size. For intricate details, a 0.25 mm nozzle may be used but requires slower speeds.
Slower print speeds enhance surface finish, dimensional accuracy, and layer adhesion. Consistent, well-tuned cooling prevents warping and stringing, particularly for smaller features or bridging sections.
Field insight: Aggressive cooling benefits PLA but can harm layer bonding in ABS and Nylon. Material-specific tuning is essential.
FDM parts exhibit anisotropic properties, meaning strength varies depending on layer direction. Layers are inherently weaker along the Z-axis due to interlayer bonding limitations.
Orient critical load-bearing features horizontally to align with stronger XY-plane bonding.
Mounting holes should face upward during printing to maximise tensile strength around fasteners.
Field insight: Printed parts under shear loads parallel to the Z-axis risk delamination. Adjusting orientation can improve tensile strength by 30-50%.
Many FDM parts require light post-processing to achieve functional or aesthetic requirements. Allow clearances for:
Threaded inserts or helicoils
Tapped holes
Sanding or surface smoothing
Painting or chemical smoothing (e.g. vapor smoothing for ABS)
A clearance of 0.2-0.5 mm for mating surfaces simplifies assembly after post-processing.
A Midlands-based robotics startup used FDM to prototype actuator housings for robotic arms. Their initial designs consistently failed during load testing due to layer delamination at bolt mountings.
After consulting an FDM design engineer, they implemented several changes:
Rotated the part 90 degrees to align bolt holes along the stronger XY-layer plane
Increased wall thickness from 1.5 mm to 3 mm
Added internal fillets to eliminate sharp internal corners
Switched from PLA to PETG for superior interlayer bonding
The redesign eliminated structural failures, enabling the company to move into small-batch production with repeatable part performance.
Field insight: Orientation adjustments alone solved 60% of the part’s failure issues, highlighting the importance of design-for-manufacture expertise in FDM.
For large flat areas susceptible to flexing or warping, integrate ribs or gussets into the design. These features add rigidity without substantially increasing material consumption.
Where applicable, design threads directly into the model using optimised 3D printing thread profiles. For high-load threads, apply metal inserts post-print.
Leverage slicer software simulations to identify weak points, thermal gradients, and potential print failures before production.
Store hygroscopic filaments such as Nylon, PETG, and TPU in sealed, desiccated containers. Moisture absorption leads to poor surface finish, stringing, and weakened interlayer adhesion.
Field insight: A single 24-hour exposure to humid air can degrade some filament types enough to impact print success.
| Material | Strength | Ease of Printing | Applications |
|---|---|---|---|
| PLA | Fair | Very Easy | Prototypes, concept models |
| ABS | Good | Moderate | Functional prototypes, enclosures |
| PETG | Very Good | Easy | Fixtures, production aids |
| Nylon | Excellent | Difficult | Gears, hinges, high-load parts |
| CF Nylon | Exceptional | Advanced | Structural, aerospace tooling |
Field insight: For most industrial prototypes, PETG offers the best balance between mechanical strength, thermal stability, and printability, making it a default choice for many production engineers.
Designing unsupported overhangs greater than 45 degrees
Walls thinner than 1 mm
Ignoring anisotropic (layer-directional) strength properties
Undersized holes without compensation for shrinkage
Excessive unsupported bridges beyond 10 mm
Field insight: Even experienced CAD engineers transitioning from CNC or injection moulding frequently overlook FDM’s specific print limitations.
Even the best design fails without proper filament choice. See our guide on choosing the right FDM material for insight into strength, printability and environmental suitability.
Initial prototype printed with conservative infill and wall settings.
Mechanical testing under simulated use conditions.
Failure analysis to identify weak points (orientation, layer adhesion, geometry).
Redesign incorporating reinforced geometries, orientation adjustments, and material optimisation.
Reprinting and retesting until the required performance envelope is achieved.
Field insight: Iterative design cycles incorporating print feedback reduce costly production failures later in the product lifecycle.
General tolerance: ±0.2 mm for most dimensions
Holes: May require post-process drilling or reaming
Flatness: Expect slight warping on unsupported large flat surfaces
Designers should specify functional tolerances only where critical, leaving generous clearance elsewhere to improve print success rates.
UV exposure: PLA and ABS degrade faster than PETG or Nylon
Temperature: PLA softens around 60°C, PETG stable up to 80°C, Nylon up to 120°C
Chemical resistance: PETG outperforms PLA and ABS for most solvents
Field insight: For outdoor enclosures or industrial machinery guards, PETG’s combination of UV stability and toughness makes it ideal.
With optimised design, FDM is increasingly used for:
Production jigs and fixtures
Robotics end effectors and housings
Custom enclosures for electronics
Replacement parts for legacy machinery
Aerospace tooling and composite moulds
Field insight: UK manufacturing SMEs frequently adopt FDM to reduce lead times for legacy spare parts no longer supported by OEM suppliers.
To see how these design principles are applied in different sectors, visit our overview of real-world FDM use cases.
Use thicker walls, higher infill percentages, optimised print orientation, stress-relieving fillets, and select materials appropriate to the load case. PETG and CF Nylon are excellent choices for functional parts that require high strength.
Minimum feature size: 0.4 mm. Wall thickness: 1.2 mm minimum, 2-3 mm preferred for functional parts. Overhangs: 45 degrees maximum without supports. Bridges: up to 10 mm without drooping when properly cooled.
Yes, with appropriate design. Overhangs greater than 45 degrees generally require support structures. Short bridges (under 10 mm) often print successfully without support if cooling is optimised.
Minimum of 1.2 mm for simple prototypes. 2-3 mm is recommended for load-bearing parts. Components under high mechanical stress may require 4 mm or more.
PETG offers a strong balance of printability and durability for most industrial applications. Nylon and carbon fibre composites deliver maximum strength but require careful print preparation and environmental control.
By fully understanding FDM design principles, engineers can produce highly functional, reliable parts for industrial and commercial applications. Optimal results require careful consideration of orientation, wall thickness, infill, material selection, and post-processing allowances.
Our team regularly assists UK manufacturers, engineers, and designers in optimising their designs for successful industrial FDM prints.
Get a 3D Printing Quote to discuss your next project or explore our full Technologies Overview for additional manufacturing options.
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