How to use boolean to cut holes in planes?

scissors .blend (463 KB)

Im pretty new to Blender and started to try model some random stuff. I noticed like to use Plane and delete 3 of the 4 vertices and just keep extruding and tracing my background image. then closing it and extruding and adding faces to the top and bottom. but I noticed when I do this and try to cut or stamp a shape with the same method, the boolean mod doesnt work.

The file I attached is me trying to boolean mod the smaller triangle and make like that shape sunken into the base piece. So I dropped the shape down a little more than half way and was trying to use boolean, but with no success. It doesnt give me an error, just doesnt work. I know I must be doing something wrong, just need pointers of whats wrong.

The normals of your Boolean cutter are inconsistent. Some are pointing inward, some are pointing outward - in other words: your mesh quite literally turns inside out in parts.

Therefore Blender can’t figure out what the inside and the outside of that object is, which is bad, because Booleans are supposed to work with solid objects.

Select the cutter object, Tab into Edit mode, hit A to select all and then Ctrl-N to recalculate the normals.

Oh ok recalculating to normals worked like a charm. So in the future, how would I go about not making it all inward and outwards and inside out? Is it how I close the vertices? or when I extrude the single vertice?

This is not entirely avoidable. With any new face you create, Blender tries to make an educated guess about the intended direction of the face normal - and sometimes that guess simply is wrong.

Therefore Ctrl-N is actually a good friend of yours.

Blender gives you a few hints about wrong normals, though: The “backside” of a face is e. g. shaded in a darker color than the “frontside”. This might seem subtle at first, but is quite prominent once you got the hang of it.

If you want to know for sure, enable the display of face normals in the viewport settings.