[Case Study]: Printing Thin-walled and Non-manifold Models - Airplanes from 3D Print Lab

This a airplane part designed by 3D Print Lab. The website is well known for their 3D printable RC airplane designs.

The plane parts, in order to be as light as possible, are designed to have a single wall with very thin inner ribs to support the mostly hollow wing structure. The author made the designs by surface modeling methods and tested the 3d prints base on Simplify3D slicer.

However some of the STL files from 3D Print Lab are "Non-manifold", in this case the surface directions are not assigned correctly. This is due to the designer try to use the outter surface as a single-walled structure to wrap other structures(the ribs) into a complex.

By default, the 3D Print Lab models will be printed OK in Simplify3D but not in UP Studio 3 due to the difference in treatment of non-manifold surfaces. 

When printed with normal settings in UP Studio 3, the inner ribs will not fuse to the wall well, as the the wall will offset into a direction base on the direction of the normals, and therefore leaving gaps between ribs and outer wall.What we need to do is to reverse the direction of the normals, in other words, transform the outer surface of the ribs into inner surface.

Here I provide a trick to flip the normals quickly in UP Studio 3:

Step 1: Select the target and mirror the model on X-axis.

Step 2: Click "Undo" button.

When Undo the mirroring, the model will have all its surface normals flipped, like following:

Now we got a model with its surface directions completely opposite to what was before.

Step 3: Select the outer wall and flip the normal.

What we want is a model with outer surface facing outward and inner surface facing inward. Now the model has inner surface facing inward but outer surface also facing inward. To reverse the direction of wall, first input command "surface" in the input field.

The software now go into "surface" mode that it will display boundary of surfaces.

Now enter command "pick s" to enable surface picking.

We are now able to select a surface of the model by clicking on it.

Click the outer surface and input command "reverse" to reverse the normal of the outer surface.

Now with surface direction being corrected, we can slice the model with "Shell" mode (Print Setting=>Special=>Fill Mode=>Shell) to print it.

If you would like the ribs to fuse more with the wall, add a small amount of negative tolerance (in Print setting =》Special tab) to make them overlap more.

* You may wonder why undoing mirroring has anything to do with surface direction? Actually this is a bug in  the software but we found it is handy at flipping normals for this situation. May be the bug will evolve into a new feature in future version! Thanks for reading.