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Apr 7

Improving Part Quality Through STL Optimization

A commonly overlooked issue when addressing poor part quality is STL optimization. The surface quality of a 3D printed part is strongly influenced by the resolution of the STL file which it is processed from; therefore, it is essential to ensure that the procedure of exporting an STL file from the native CAD file is performed correctly. As an STL file is the required format for processing CAD models in 3D printing software such as Insight and Catalyst, ensuring it is exporting with optimal settings is an important step when processing parts for 3D printing with Fused Deposition Modelling (FDM), or Polyjet processes.

What is an STL?

A STereoLithography file (abbreviated STL) consists of a triangulated representation of a 3D CAD model, and is a standard file type widely used by rapid prototyping/3D printing, computer-aided manufacturing, and additive manufacturing industries. This file format will approximate the surface of a solid model using triangles, excluding any colours, texture, or internal structure. STL files can be generated by most CAD software packages.

Figure 1. A range of end products can be achieved by changing STL export settings
Depending on the CAD software used, different parameters can be selected upon exporting the STL file. In particular, the user may have the option to select the resolution to either fine, coarse, or custom. With custom resolution settings, the deviation and angle can be adjusted separately by the user, allowing them to find the optimal balance between file size and file quality. Furthermore, outputting the STL file to a binary or ASCII format is an option. By consulting the user guide for a specific CAD software package, the options and parameters to export an STL file can further be explored.

Coarse, Fine, and Custom Resolution Settings

As mentionned previously, the most common option which will be changed upon exporting an STL file is the file’s resolution. Having an STL exported using a coarse resolution will result in a smaller file size, faster processing times, and is well suited for processing systems with less power or for producing parts without any organic surface geometries.

Figure 2. Coarse settings for STL export

However, this coarse resolution will result in a faceted surface finish in the STL file over natural surfaces, giving the final 3D printed model a rough surface appearance with large, visible triangles (as in Figure 2). For most applications, this is less than ideal, as the end product will provide a poor representation of the original CAD drawing However, for some artistic applications (ie the production of low-poly figurines), utilizing the coarse setting may, in fact, be desirable.

On the other hand, selecting a fine resolution upon exporting the STL will result in a smooth surface finish, with little to no triangles visible at all (see Figure 3). The drawback to this option is a larger file size, resulting in greater processing times in the 3D printer’s software (depending on the power of the processing station).


Figure 3: STL Optimized with Fine/Custom export settings

Though selecting a 'fine' resolution generally works for processing most parts, computers with lower specifications may get 'hung up' when trying to export files with complex part geometries. In order to overcome this issue, custom export settings may be used to find the perfect balance between STL resolution and file size for one's processing station. Here at Cimetrix, we use a custom resolution setting with the deviation tolerance set to .0014725mm, and the angle tolerance set to 7.00 degrees.Once an STL is exported with the determined resolution, there are no means to improve faceting in the 3D printer’s processing software; the surface of the 3D printed model will reflect that of the STL file. Therefore, it is essential to determine whether the paramaters that are most critical for a particular build.

To learn how to export an STL file, visit our CAD-to-STL page, which outlines the procedures for exporting a high-quality STL file for a number of popular software packages. Be sure to stay tuned for continued Tech Thursday posts, where each week one of our Applications Specialists will be providing tips, tricks, and tutorials to help you get the most out of your Stratasys 3D Printing platform. For more information, please feel free to peruse our website, or contact our team of Applications Specialists, for more information.