Do you know what can make your 3D file unprintable? Inverted surfaces, thin walls and multiple shells are all common problems with STL files. Aside from causing delays in the quoting and production process, the machine might not be able to fabricate your model.

Whether you’re exporting an STL for the first time or you’re a 3D printing pro, this guide will make sure you can fix any issues before you go to quote your 3D model for printing.

1. Are the walls thick enough?

wall-thickness-3d-printing-1.pngWall thickness is the distance between one surface of your model and its opposite  surface. Every 3D printing technology has its own required wall thickness to ensure that models can be manufactured and post-processed. As a general rule, walls need to be at least 1mm thick, but some technologies can handle smaller features. (see table below)


  Suggested tools to fix: Meshmixer (Tutorial), Your CAD software you used to design the model (most accurate option)


2. Is the model watertight/manifold?

Watertight and manifold essentially mean that there are no holes in the STL mesh (ie. if the model was submersed in water, would there be leaks?). Prints that have holes in the surface could fail to print, or not function the way they were intended. Check out this tutorial on how to fix your STL mesh in MeshMixer

stl-mesh-with-holes.jpgThe model on the left is clearly not a manifold model, it has lots of little holes in its mesh

Suggested tools to fix: Mesh Mixer (Tutorial), NetFabb


3. Will any fine features or text I have render properly based on the 3D printing technology I've selected?

Small details, such as text, need to be a certain size in order to appear on your 3D print. The smallest printable feature depends on the 3D printing technology you choose.


Suggested tools to fix: The CAD software you used to design the model


4. Is there enough clearance between any moving parts  on the model?

To ensure that movable parts can function properly, there must be enough space between features  for any support material or excess material to be removed. "Enough space" varies by technology but 0.6mm is safe. Without enough space between parts, certain features could fuse together; ruining the mobility of the design. See the table below for clearance specifications.


Suggested tools to fix: The CAD software you used to design the model


5. Are any models grouped/does the object have multiple shells?

Objects that are grouped together can confuse the 3D printer. If you have separate objects in one file, they should be exported and uploaded individually. If you have multiple shells in one object, they should be combined.

Suggested tools to fix: Mesh Mixer Tutorial (combined shells)


6. Are there any overlapping objects?

It's not just how an object looks on the outside that counts, intersections of objects on the inside of models can confuse 3D printers and make your file unprintable. Merging the objects preserves the outer shape but gets rid of thin, overlapping internal walls. This can be done by using a Boolean union in some CAD softwares or with a free tool called Mesh Mixer.


Refer  to the guidelines for your 3D modeling software for more information.

Suggested tools to fix: Mesh Mixer (Tutorial)


7. Are there any inverted or reversed surfaces (inverted normals)?

Inverted surfaces means that a surface of your model is facing the inside of the object instead of the outside. there are a number of reasons why this can happen but fortunately it's usually an easy fix inside your CAD software. Some softwares show inverted surfaces as shaded and will allow you to fix it in just a few clicks. For help fixing inverted surfaces, try a cloud repair solution such as Netfabb

Suggested tools to fix: Netfabb


So now that you’ve checked your wall thickness, surfaces, small features, objects, shells and tolerances, you’re ready to export your file for 3D printing. Check out our guide for exporting an STL file from CAD programs.


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