hi NP5
thank you for your answer. but i dont know how i can use extrusion to make baking. somehow i have the feeling you dont mean the command Grant explains us in edit mode with the e keystroke… 
i found today a metode described by another member of the community. Cavity Map won’t bake - Blender Courses / Ask - GameDev.tv
this method worked rely good. i had to rewatch the video thou to remember how to make the baking. i have the feeling there is a lot to remember… i see no chance to remember all this, i dont see any logic in this (yet) just pure remembering, making notes or rewatch the video. where i think to rewatch is the most easy.
i think this video course is awsame! the community great! its so enjoyfull to learn all this new things. i`m blown away with the progress!
on this point again a big thank you to all!
this is now the low poly in render mode
