Converting ASCII STL files to binary


If you are using Autodesk 123D Design to create your 3D models, you may have noticed that XYZware can sometimes be very slow to import the model.

13 xyzware stall
XYZware screen of death when importing a 123D Design model

XYZware will just sit there churning away for several minutes until the model is finally loaded. However, once the model is loaded, things don’t get better. If you begin the slicer, slicing can take even longer or you give up.

The problem appears to be due to the two formats of *.STL files; ASCII and binary. In a nutshell, XYZware doesn’t  handle ASCII STL files efficiently and Autodesk 123D Design only exports models in ASCII STL files. However this can be fixed easily.

ASCII versus Binary STL Files

A model saved as an ASCII file or binary file type will contain the same information. The only difference is the method of encoding the information.

An ASCII STL file will have the data encoded in letters and numbers that a human can read.

ASCII stl file

Whereas a binary STL file will be indecipherable to a human.

Binary stl file
Binary STL file

Encoding the data in a binary format uses much less storage space than ASCII and hence less RAM is consumed when loading a binary file into working memory.

17 file sizes compared
ASCII and Binary file sizes for the same model are significantly different

Converting an ASCII STL File to Binary

To demonstrate how straightforward it is to convert your STL files into binary format, I’ll show you each step I use in my work flow. The demo model is a Pac Man Ghost screwdriver holder that you can print yourself.

1. Saving Your Model in 123D Design

Your model is complete and you are ready to export the model as an STL file. I choose coarse tessellation because it results in smaller files and has always worked well. Give your model a name and click save.

2. Start Meshmixer

When you installed Autodesk 123D Design, you would most likely have installed Meshmixer too. Meshmixer is the tool that is used to generate the binary STL file and you can find it by searching for Meshmixer in the start menu.

 3. Importing Your Model

Once Meshmixer is running, click the Import tile on the start screen.

4. Exporting as a Binary STL File

Exporting as a binary STL file is simple. Choose export from the file menu and choose the location to save the file. Ensure you choose “STL Binary Format (*.stl)” from the list of file types. I like to end the file name with binary so I can identify which format the STL file was saved as. Then click save.

You’ll notice that there is a big difference in size between ASCII and Binary STL files for the same model. The ASCII format file is 29.9MB and the binary is only 5.4MB.

5. Done!

That’s it. Simple.

Now when you import your binary format STL files into XYZware, you’ll notice your models are loaded almost instantly and slicing is much faster.



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