A Guide to STL Files for 3D Printing Projects: STL vs. CAD Models and Other Critical Info

Creating a custom STL file for your parts is one of the crucial early steps in the 3D printing process. Essentially, an STL file is a 3D model that precisely describes the surface geometry of your part as a complex structure built up from interlinked triangles.

We’ll delve further into the specifics below, but the short version is that the STL format is the most efficient way to model a 3D structure for the additive manufacturing process.

STL Files vs. CAD Files

STL files are often compared and sometimes confused with the commonly-used CAD file type. Short for stereolithography (as well as the backronyms Standard Tessellation Language / Standard Triangular Language), STL files were specifically developed for compatibility with additive manufacturing systems.

In contrast, CAD (computer-aided design) files create 3D models of parts for use on various machining systems, in metalworking, in custom molding, etc. CAD files precisely describe the surface structure and geometry of the part, but not in the most efficient terms for 3D printers (i.e. triangular tessellation).

The Basics You Need to Know About STL Files for Your 3D Printed Parts:

Modeling Each Part as a Triangular Mesh

As mentioned above, STL files describe the 3D model of your part as a collection of interconnected triangles. Analogously, the triangles are built up and linked together like tiles on a floor or shingles on a roof – except it’s a far more complex form of tessellation.

If you picture the way 3D printers deposit materials, you can maybe imagine why a structure of triangles works efficiently: the machine essentially “slices” the part into thin 2D layers as it processes instructions in order to interpret the 3D model.

A Closer Look at Those Triangles

Each triangle is defined by three vertices within 3D space. Every vertex has X, Y, and Z coordinates specified in the STL file. These coordinates essentially create boundaries for the 3D printed material once the machine is running, and ultimately reproduce the shape of the final part.

Each triangle in an STL file also has a specified normal vector perpendicular to the plane, which indicates its orientation in space. Normals are crucial for determining precise orientation of the front and back side of each triangles to ensure complete accuracy.

The Importance of Your Mesh Resolution

The quality of each 3D printed part largely depends on the resolution of the triangular mesh described in the STL file. A higher resolution results in a more accurate representation of the original model. However, the downside is that higher resolution also leads to larger file sizes, slower printing speeds / less throughput, and the potential for more manufacturing errors.

Solid and Shell Structure Parts

STL files can represent both solid and shell structures, basically for solid or hollow plastic parts. In a solid STL file, the triangles define the outer surface of the part as a closed 3D shape. In a shell STL file, the triangles represent a surface without defining the enclosed volume, which is ultimately hollow.

Manifold or Solid Surface Geometry

A proper STL file should define the surface of the part as a manifold geometry – a solid, uninterrupted surface. Non-manifold models tend to cause issues during production because the holes or gaps cannot be sliced properly by the printer.

Units, Scale, Color, and Texture

STL files do not inherently contain information about units or scale. It’s therefore essential to export the 3D model with the correct scale. STL files also generally lack information about part color or texture, so these details must be otherwise specified.

The Michigan Region’s Leading Additive Manufacturing Specialist

Elite Mold & Engineering is one of Michigan’s leading manufacturers offering custom 3D printing services. Established in 1982, we’re backed by more than four decades of delivering superior quality plastic products made in the USA.

Published: February 7, 2024

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