I am a 3D sculptor making figurines that are 3D printed then mass produced from that prototype and the biggest problems I encounter in 3d prints is a pocket in the model with no escape hole causing the surface above that pocket to crack. The second biggest problems is wall thickness being thin enough to crack when printing. Even with the Preform slice slider, it can be difficult to tell where pockets are that have no escape holes and if a particular wall thickness is thick enough because of all the geometry going in all directions from draping cloth on dresses and whatnot. I would like to recommend that Preform includes a notification, and maybe even an option to auto-fix, when a wall thickness is too thin or there is a sealed pocket in the figure when you load the figure into Preform. I recommend this way instead of when printing because then contractors like me, who only send files to the client that has the 3D printer, will be able to know of the problem and fix it before sending to the client.
Closed “pockets” inside a model are called “shells”. 3D printing post-processing tools like NetFabb will find and remove these internal voids for you. They will also find many other 3D modeling defects that can negatively affect a print. PreForm actually uses some core technology from NetFabb to process your model when you load it. But internal shell removal isn’t one of them, so you might consider downloading even the free version of NetFabb to run on your files before you send them out. The free version won’t get rid of extra shells, but it will tell you if they’re there or not and you can go back to your CAD software to hunt them down and delete them.
As for wall thickness, PreForm can’t possibly guess your intent. For example where I might print something that’s only 1mm thick on purpose you might not be able to use anything with a thickness less than 10mm. How does PreForm know what our expectations for the print are? As the designer, it’s usually our responsibility to make sure our output is something that the fabrication process can actually fabricate.
Thank you for the tips! The NetFabb sounds like it would be helpful to check for shells, especially if just the free software can do that since that is really all I need that I can’t do in Zbrush.
As for the wall thickness, I would just like it to let me know what areas of the figure have a wall thickness that might be too thin and cause printing problems. I make the figurines hollowed out to save on printing material but when they’ll be mass produced they’ll be solid. We originally used Shapeways for 3D printing before the client bought a Form 2 and Shapeways model uploader alerts with red coloring where wall thickness is too thin and will likely cause a printing problem. That’s all that I meant for the Preform to tell where wall thickness was too thin, to alert where printing will likely break from wall thinness. Since there’s no real rulers in the Preform software I kind of just have to eyeball the wall thickness and guess if it will be thick enough in some areas.
PreForm could certainly do what you’re saying, but I don’t think that it does.
I think MeshMixer (or whatever it’s called now) will hollow out a solid object for you. You can specify the minimum wall thickness and it will honor that even if it means it can’t hollow out some areas. Note, though, when printing on a Form2, especially hollow objects with thin walls, you will probably need vents, holes from the inside to the outside, positioned at the top (near the build platform so that once the opening is printed, it will be above the resin for the remainder of the print. (think “inverted cup with a hole in the bottom, with the bottom of the cup towards the build platform”).
Thank you for the help! I will definitely go check out MeshMixer. If it can hollow things out easier and better than how I’m doing it in zbrush manually I will definitely use it. I hope Preform will be able to do these things someday 
You’ve been super helpful, thanks!
Hi LDavis,
Take a look to this webinar https://formlabs.com/3d-printing-for-digital-sculptors-webinar ,
you will see an easy way to automatically hollow things with ZBrush (it’s a one click command).