Inspire 2015- Choice Of Units Affects Size Of Exported Stl Files- Bug?

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

I don't know if anyone else has noticed this, but in Inspire 2015, if you do a 'Save As... STL' to directly export your optimized result to 3D printing, sometimes the 3D printing software (in our case, Catalyst because we use Stratasys printers) makes the STLs 30.5x too small! 

 

This puzzled us for a long time, because if the size was 2.54x too small or 25.4x too small, we could say, yep, that's a units mismatch between inches and centimeters (2.54) or inches and millimeters (25.4).  But 30.5?  What was that?

 

It took us a while to realize that 1 foot is 30.48 cm, and while the size of the model was always the same in Inspire no matter what units you choose, the size of the EXPORT somehow changes with the units set in Inspire! 

 

Now, if you open the exported STL in a CAD program (SolidWorks for us), the size of the STL will always report the same no matter what units you choose in Inspire, but there seems to be something with how Inspire creates STLs, some field for 'units' that the Inspire properties are filling in, that makes some 3D printing softwares not open the STL correctly.

 

I don't know if it happens in all 3D printing softwares, but we've hit this problem the last two times we've printed straight from Inspire, and I wouldn't have expected the choice of units would change the actual size of the STL, just the reported units of it. 

 

Just thought folks should know. 

Shuvom Ghose

shuvom@capinc.com  

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited November 2015

    In the STL file format there is no units i.e. units are arbitrary. Inspire will save in the current length unit you are using and mention that unit at the top of the files. Some 3rd party software will read that unit field and convert size as needed. If the sofware you are using do not perform that conversion you will need to set Inspire to the lenght unit they expect before exporting a STL file.

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited November 2015

    Matthieu,  

     

    Thank you, that's exactly the behavior we seem to be experiencing.  I just thought folks should know the workaround if they are experiencing problems with direct 3D printing out of Inspire like we are. 

     

    That's interesting that STL files are unitless, I didn't know that before.  That explains a lot about this issue.

     

    Thanks!

    Shuvom

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