The Tools

The toolset used for this project is BLENDER (https://www.blender.org/) and CURA (https://ultimaker.com/en/products/ultimaker-cura-software).

BLENDER (God bless Ton Roosendaal) is used to design the 3d models and CURA to prepare the models for 3d printing.

Related to BLENDER I found a very helpful articel about preparing blender files for 3d printing. Reading it is a must have
https://daler.github.io/blender-for-3d-printing/contents.html
https://www.shapeways.com/tutorials/prepping_blender_files_for_3d_printing
https://www.sculpteo.com/en/tutorial/prepare-your-model-3d-printing-blender/
https://www.shapeways.com/tutorials/fixing-non-manifold-models
https://www.shapeways.com/tutorials/creating-hollow-objects


Here comes a list of collected and helpful keyboard shortcuts of blender.

in edit mode:

ALT+CRTL+SHIFT+m  :  is each mesh manifold (water tight) check
f  :  fill / face creation an edge or face / combine two vertices / makes a line between 2 vertices
CTRL+f  :  grid fill
SHIFT+h  :  hide rest - keep only the selected vertices
p : separate selected vertices to a single object
CRTL+t  :  triangulate all selected faces
w  :  specials menu -> remove doublets
i  :  inset a face / like extruding only in one dimension / current face layer
ALT+m  :  unify the model / merge the selected edges / fill in this way / monkey eye example
k  :  knife  - select a face and apply knife
CTRL+b  :  bevel model - add a cube and test it
CTRL+e  :  bridge edge - close a gap between objects - bride edge loops

in object mode:
ALT+CTRL+SHIFT+c  :  set origin to 3d cursor
SHIFT+s  :  set cursor to / set object to context menu

in general:

t  :  toolbox hide/show docked on the left side
n  :  transform, position, scale information hide/show docked on the right side.
z  :  changing between solid and wireframe view