3D File Preparation
We’ve created this guide to highlight the most common issues we encounter when processing 3D files for printing.
Our goal is twofold: to simplify the quoting process and to minimize or eliminate additional costs that may arise from repairing files before production.
Properly preparing your file ensures a faster, more efficient workflow, allowing us to move straight from quote to print — saving both time and resources.
Understanding 3D Topology
3D printing is a manufacturing process that physically reproduces a digital model, capturing every detail of its geometry.
The standard file format for 3D printing is STL, which represents the model using a triangular mesh.
If your model was created in CAD software or NURBS-based 3D modeling programs — which define shapes through mathematical curves — it must be converted to STL format for printing.
This conversion can lead to significant changes, especially in areas with curved surfaces or organic shapes, where polygonal approximation replaces smooth geometry.
To ensure a successful print, it’s essential that the STL file maintains proper resolution, watertight geometry (manifold), and clean topology.
Poorly converted or low-resolution files may result in printing defects, surface artifacts, or the need for manual corrections — which could delay your order and incur extra costs.
As shown in the images, the mesh detail (Image 2) reveals a noticeable change in geometry. Curved areas appear more faceted or polygonal, rather than smooth. This happens because, during STL conversion, the entire geometry is simplified into triangles. As a result, a cylindrical shape becomes an n-sided polygon, and fillets or rounded transitions are broken down into flat surfaces at varying angles.
This detail is especially important in the context of 3D printing, because a low-resolution model (Image 3) will print exactly as it appears — with visible facets and a polygonal look.
To achieve a printed part that closely resembles the original CAD design, it’s essential to increase the resolution during STL export (Image 4). This will generate a higher number of triangles and produce a more refined, accurate mesh.
Keep in mind, however, that higher mesh quality also increases the file size — which may require optimization before uploading, especially if your model exceeds the upload limit.
For best results, we recommend exporting with high detail settings while maintaining a balance between resolution and file size.
Impact on Functional Parts
Mesh simplification doesn’t only affect the visual appearance of the part — it can significantly impact functional geometry as well.
Take the component shown in Image 1, for example, in its original CAD version. In the modeling software, we simply defined the hole diameter as a numerical value (Image 5). However, once the model is converted into a mesh, even circular holes are approximated into polygons.
As shown in Image 6, the resulting mesh version of the hole becomes a polygon inscribed within the original diameter. This means extra material remains in the internal profile, potentially causing clearance or interference issues during assembly — for instance, when inserting a pin or shaft.
This geometric simplification can lead to poor fit, tight tolerances, or even mechanical failure if not accounted for during the design-to-print transition.
For any part that includes mechanical features or mating elements, we strongly recommend:
Exporting the STL with high resolution
Manually verifying critical dimensions post-conversion
Allowing for mechanical tolerance adjustments during modeling
When in doubt, feel free to contact our technical team — we’re here to help ensure your parts function as expected, both digitally and in the real world.
Topology – Final Considerations
As we’ve seen, the main issue with converting CAD geometry for 3D printing lies in the way curved surfaces are simplified into triangular meshes.
From a visual standpoint, it’s important to decide what level of surface resolution is acceptable for your curved geometries. We always recommend previewing the STL file — even with a basic 3D viewer such as the one included in Windows — to compare the mesh to the original CAD model.
If the model appears too faceted or angular, simply increase the resolution settings during STL export from your 3D software. This ensures a smoother, more accurate surface.
When it comes to functional features, particular attention should be paid to geometry conversion in critical fits, such as pins and holes. During mesh conversion, perfectly round elements become polygonal, which may lead to interference and non-conforming parts.
Our recommendation is to apply dimensional tolerances directly during the modeling phase, before exporting the file. Using nominal values for mating parts (e.g., hole = 10 mm, pin = 10 mm) will likely result in fit issues due to the extra material generated in the mesh approximation.
We’re more than happy to assist with file adjustments if needed. However, for any functional or mechanical parts, we strongly suggest that you also send us technical drawings with precise dimensions and tolerances. This helps us apply the correct adjustments during the preparation phase and avoid the types of issues described above.
File Integrity Guide: Manifold vs. Non-Manifold Models
File integrity is one of the most critical aspects of successful 3D printing. Even with the best materials and equipment, a poorly prepared file can result in failed prints, dimensional inaccuracies, or defective parts.
One of the most common issues we encounter involves non-manifold geometry — models that, due to structural or topological errors, cannot be interpreted correctly by the slicing software.
🔍 What Does “Manifold” Mean?
A manifold model is a watertight 3D mesh where every edge is shared by exactly two faces. It defines a solid, printable volume that slicing software can process without ambiguity.
⚠️ Common Non-Manifold Issues
Intersecting or overlapping geometries
→ Two or more objects occupy the same space or intersect improperly, causing internal artifacts.Holes or open surfaces
→ The mesh has missing faces, edges, or unconnected surfaces, making it unprintable as a solid.Inverted or mixed normals
→ The orientation of surfaces is inconsistent, leading to areas that slice incorrectly or appear “invisible.”Zero-thickness surfaces or edges
→ Paper-thin elements that have no actual volume, often ignored during slicing.
These issues almost always result in errors during printing — such as shifting layers, missing material, or structural weaknesses in the final part.
📸 See It for Yourself
Below we’ve included real examples of non-manifold errors, showing how they appear in 3D software and how they affect the printed output. Understanding these cases will help you spot and correct them before uploading your model.
For optimal results, we always recommend using manifold geometry only, and checking your file in a mesh validation tool (such as Netfabb, Meshmixer, or Blender) before submission.
Open Geometry Issues
One of the most frequent issues we encounter involves open geometries — models made up of surfaces that do not form a closed, watertight volume.
These models are typically non-printable, as they lack the thickness and solidity required by slicing software to generate valid toolpaths.
Open-surface models often result from:
Exporting surfaces from CAD without assigning a volume
Incomplete designs where faces are missing or improperly joined
Accidental deletions or modifications in modeling software
To be considered 3D printable, a file must represent a closed solid (manifold), where every surface is properly connected and defines a valid internal volume.
Even though the 3D viewer may display an open model visually, it will fail during slicing or produce unexpected results during printing — such as holes, missing walls, or fragile, unusable parts.
✅ Solution:
Always ensure your model is fully closed before exporting. Use mesh repair tools or solid modeling functions in your CAD software to validate the geometry. Most modern 3D tools offer a “solid check” or “manifold verification” feature for this purpose.
Models with Shared Vertices
Another common issue arises when multiple parts within a model share vertices but are not properly joined into a single solid. These are typically separate bodies that touch or intersect at specific points but have not been merged into a unified geometry.
Although these parts may appear connected visually, the slicing software interprets them as ambiguous or invalid geometry, making the file unsuitable for 3D printing.
This problem often occurs in assemblies where:
Components were exported together but not combined
Separate shells were modeled with overlapping geometry
Vertices are connected but faces and edges are not merged
🚫 Why It Matters
Files with shared vertices but no true union will fail during slicing or produce artifacts in the final print — such as internal voids, surface inconsistencies, or complete print failures.
✅ Recommended Fix
When parts are meant to be printed as a single object, ensure they are properly joined and fused within your 3D modeling software before exporting.
If instead they are distinct components, they should be exported as separate models to avoid geometry conflicts.
We’re happy to assist in separating or merging models where needed — just let us know during the quote request.
Inverted or Partially Inverted Normals
Normals are directional vectors that 3D software assigns to the faces, vertices, and edges of a mesh to define the orientation of the geometry. They play a crucial role in how the slicing engine interprets the surface of a model during 3D printing.
In polygonal modeling, it’s not uncommon for normals to be inverted — either entirely or partially — due to modeling errors, mesh imports, or Boolean operations.
When normals are pointing inward instead of outward, the slicer may interpret those surfaces incorrectly, resulting in:
Missing or invisible faces
Thin walls being skipped entirely
Unpredictable slicing behavior
Failed or structurally weak prints
✅ Best Practice
Before exporting your file, ensure that all face normals are consistently oriented outward. Most 3D modeling software offers a built-in tool to recalculate or unify normals across the entire mesh.
For example:
In Blender: “Recalculate Outside”
In Meshmixer: “Flip Normals” or “Make Solid”
In Fusion 360: “Repair Body” via mesh tools
Checking and correcting normals is a quick but critical step to ensure a successful print.
Zero-Thickness Surfaces (Shells)
Another common cause of non-manifold geometry is the presence of zero-thickness surfaces, often referred to as shells.
These are models made up of hollow surfaces without any assigned thickness. While they may appear complete in a 3D viewer, they do not define a solid volume and therefore cannot be processed for 3D printing.
In slicing software, a model without thickness:
Has no measurable volume
Cannot generate valid toolpaths
Will result in errors or empty layers during printing
This issue is typical of models exported from surface modeling workflows, or when designers forget to “solidify” the geometry during the final steps.
✅ Solution
To make a model printable, the geometry must have real-world physical thickness, just like an actual object.
You can resolve this by adding thickness using functions such as:
“Solidify” (Blender)
“Thicken” or “Shell” (Fusion 360, SolidWorks)
“Offset Surface” with wall thickness (various CAD tools)
Be sure to apply a minimum wall thickness compatible with your chosen material and printing method.
Intersecting Geometry
Models that contain internal geometry or overlapping parts are considered non-manifold and will likely cause issues during slicing and printing.
These intersecting elements may include:
Hidden internal walls or components
Duplicated meshes occupying the same space
Overlapping bodies that were not properly merged
While these issues may not be visible in a 3D viewer, they create ambiguities in the model’s volume, preventing correct toolpath generation and leading to defects such as:
Voids or unwanted internal supports
Print instability
Material waste or printing failure
✅ Solution
To ensure the model is printable:
Clean the geometry by removing all internal or overlapping parts
Keep only the visible, external surfaces that define the final object
Use Boolean union operations or mesh cleanup tools to merge intersecting bodies correctly
Most 3D design software offers validation or cleanup features to detect and fix these issues.
Conclusion
This brief guide was created to highlight the most common issues that can arise when preparing 3D models for printing.
We fully understand that it’s not always feasible to check every detail or to model exclusively with 3D printing in mind — especially during the early stages of design.
However, by being aware of these potential pitfalls and taking a few extra steps during modeling and export, you can significantly improve the printability and reliability of your files.
Providing a clean, optimized, and compliant 3D model helps us move straight to production, reducing delays, eliminating the need for manual corrections, and avoiding additional costs.
If you’re ever unsure, our team is here to support you — from technical reviews to minor repairs, we’re committed to helping you bring your projects to life with precision and efficiency.
