STL to DWG to STL Problems... I want to print!

[rickyh2007]

Background: Hello and good day. I am a student in high school, still relatively a novice in AutoCAD. We are constructing phone cases, and I decided to use one that I downloaded from Thingiverse.com as a base to start with. When I downloaded it, the file was an stl file, ready to go. I, however, wanted to alter it. Therefore I found a converter, opened up the DWG in AutoCAD, scaled it from millimeters to inches, and began editing. I needed to print out a prototype to make sure the dimensions will fit my phone before I continue. I exported the file from the DWG in AutoCAD 2015 to an STL to be opened in, oriented, and printed through CatalystEX. But...

Problem: The object that appears in Catalyst is a ridiculously small rectangular prism with no subtractions. It is just a rectangular prism... even if my phone was an inch or less long, the box would have no slot to stick my phone into...

I tried the original downloaded STL file, and it works fine (Catalyst asks to use millimeters as a unit). However, when I export the (converted) DWG file back to STL, even if I do not scale it, the same result occurs (although larger if I keep the STL in millimeters while the Catalyst program is defaulted to inches).

Question: What is happening and why? Can I even use the original STL file that I downloaded? Is there some way I can work around this, mabe just copying and pasting the work I have already done onto a new AutoCAD project? I figured using the downloaded case as a base would save me a lot of work, but it seems to be more work than it is worth... 

Thank you for your time!

-Ricky Heath, rickyh2007@gmail.com 

[JDMather]

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@rickyh2007 wrote:

Background:  When I downloaded it, the file was an stl file, ready to go. I, however, wanted to alter it. Therefore I found a converter, .... 

Problem: The object that appears in Catalyst is a ridiculously small rectangular prism with no subtractions. ....

Question:  Can I even use the original STL file that I downloaded? ...

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Background:  stl files are coarsely faceted planar surfaces (not solids) generally of little use in an design program (these files are for printing).  What converter did you use?  (Try Fusion 360 or the mesh to solid converter add-in for Autodesk Inventor) When you ran the List command on the converted file - did it list your Properties as a 3D Solid body? 

Problem: In AutoCAD type the command -dwgunits with the preceeding minus - sign.  Examine the command line - what does it really really really say your document units are?

Question:   (if you zip and attach your stl file here - I can convert it to a solid for you in Inventor)

[rickyh2007]

Attached is the original downloaded STL file nevermind it is not supported... I attached the original zipped file that I downloaded (I will link you to the source where you can download it as well). I tried using Inventor to export it: The exported file (although opened) was a blank slate in AutoCAD. I tried using 3DS Max: The DWG file opened successfully but cannot be exported ("Mesh not converted because it is not closed or it self-intersects"). The -dwgunits command showed that it was in inches, as I expected. But the phone case's original dimensions are in millimeters. Thank you very much for your assistance. I am utterly clueless when it comes to things like this, especially intercompatibility.