Problems with STL model in Ultimaker Cura

I want to print a piece of fruit modeled in Blender. It is an STL file. Please note that I am an absolute beginner at 3D printing models.

What do these red zones mean? What is wrong about the mesh in each case?

The fruit has some low-poly seeds. These used to be a particle system but I then changed them into individual objects.

This view shows the base of the fruit, why is it colored red?

• Welcome to 3DPrinting.SE! Nov 10, 2018 at 0:01
• Red areas indicate parts of the model where you should expect troubles when printing them. In most cases a support structure will make them printable. Nov 10, 2018 at 2:13

2 Answers

3D printers cannot print in the air without a prior layer or a support structure supporting the new printed layer. For the picture showing the bottom of the fruit, the red area is the calculated area that requires support for printing, so please enable that in the slicer application.

For the top picture please post a detail or a zoomed in part. It is currently difficult to see what is the matter. It looks as though the STL model is incorrect and Ultimaker Cura thinks that the seeds are upside down, hence the red coloring also. This means that you need to fix the normals of the faces in the STL model. Please look into this answer and this answer for some hints.

Red is the color Cura uses to mark overhang areas. For the bottom that is normal, it can be fixed by using support.

For the top, the presence of red atop the seeds is a common tell of inverted normals in the seeds.

To fix, open your .blend file again, choose the seeds and flip normals. To make the whole thing even better, choose both the fruit and the seeds and then apply the union modifier on both.