I recently stumbled upon a bizarre issue. I had this 3D model I had created in Autodesk Fusion 360 and it looked great, albeit strange due to the supports I added around it.
It rendered properly on MakerBot Desktop, and I figured that I could just print it without issue and come up with something similar to my design and then perfect it later. Here’s what I ended up with:
Woah where’s the cavity? Why is it filling it in? I took a look at the print preview and how the slicer was splitting up the layers only to find that it had filled in the box!
I couldn’t figure out why the rendering showed it with a cavity but the printer was receiving instructions to fill it in. I thought that it might be the combination of Autodesk Fusion 360 and Makerbot Desktop software that is the problem, so I called them to ask about it. It turns out that it happens across the board from time to time with different 3D modeling software. Prints don’t necessarily turn out the same way they’re rendered, especially with more complex designs. (That’s how I learned to always check the print preview on a 3D printer. No one wants to spend a couple of hours on a wasted print.)
I heard about a repair tool that might help called Netfabb, so I decided to try it out and see how well it would perform. I can’t speak for the full downloadable tools, but I found out that they have a cloud service (https://netfabb.azurewebsites.net/) which will allow you to upload your STL files, repair them, and then download the fixed version (free as long as it’s for non-commercial use). This fixes some of the issues you might be seeing with your prints. (Remember to double check them through the print preview though)