Good afternoon (o;
Having this as a base body for a speaker case:
But when I want to create a shell the limit is here 3mm thickness…but even then it creates holes in the body:
And from the inside it looks I wouldn’t expect at all:
So don’t know why it creates those strange cutouts inside…which look like an extension from the cutout at the front corners…
Any ideas why this is happening…or better…how to make it better?
thanks in advance
richard
Hi! The Shell can be imagined as an offset surface while keeping the solid body by defining a wall thickness. The tool is super powerful on simple shapes, but even if there is a small fillet or two edges that may intersect after being offset, it fails to maintain manifold solid bodies. If surfacing is supported, the tool moves on by telling the user the solid body was split up to an open polysurface.
Normally it would be a generous safety feature to avoid manufacturing issues, but since 3D printing is here to overwrite the regular manufacturing rules, well, we have to find some new solutions to create models 
In your case, I’m afraid the bottleneck is the decreasing distance between the inner edges of the embossed detail and the inner face of the sphere. This is what can be seen on the second uploaded picture. That detail is not a hole, it is the edge inside the sphere. The reason why you can see that edge is that the line thickness is bigger than the actual distance between the outer face of the sphere and the edge itself.
One possible workaround would be to project the contour of the embossed detail to the sphere and shell the sphere out from the projected section. Then create the embossed detail as an independent solid body with the required thickness and merge the two bodies together.
Projection doesn’t work in my case…as soon I use the projected surface it scales down towards the inner center of the sphere…so I did the shell first without any cutouts…
Now added a second sphere, cutout the speaker profile as well as the required thickness with a slanted rectangle:
Now I can union the original ball with the new cutted out section:
And apply fillets:
Slowly but surely getting the hang of it…
Just too bad there isn’t a sweep tool with start/end scale or a better loft functionality…
Fun doing speaker design for 3d printing 
Awesome! Happy to see that you could move on with the project 
