What is an STL file?

Simply put, an STL file is a file used by sterolithography software that can be ready by additive manufacturing machines. The part is broken up into triangles, with each triangle having its normal & vertices defined. An STL file only describes the surface geometry for a three-dimensional part – no common CAD model attributes, such as colour or texture are represented.

STL files come in 2 different formats; Binary and ASCII. An ASCII STL file is readable by a human, and can be modified by a text reader, if necessary. Because of this, ASCII files have much larger file sizes than Binary & it is usually impractical to use an ASCII STL for anything other than debugging purposes. A Binary STL is not human readable, and is made up of sets of numbers to define the component.

The quality of an STL can vary a lot, depending on a number of variables. Usually, the triangles orientation must be defined correctly, and all triangles must be joined together. Specialist software for modifying STL files and small gaps & inconsistencies in the part can be fixed. However, more fundamental issues may require modification of the original CAD model. One of the variables that affects the quality (and file size) of an STL is the number of triangles. If too few triangles are defined, the part becomes very facetted and loses its original shape. If too many triangles are defined, the STL file size can become very large & may end up being unmanageable within the machine and processing software.

CAD models can normally be converted to STL within most CAD packages, by way of an automated process. As long as you have a well-surfaced 3D model, the user may be given several options to adjust the resolution of the output model – this will affect the quality of the STL file as well as the file size. Smaller or fine detailed parts may require a higher triangle count that large, simpler parts.

If you do not have access to STL conversion software, Design For 3D can provide a conversion for you as part of our CAD Design Service. For any STL conversion enquiries, please contact us on: info@designfor3d.co.uk

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