Lawn Mower Robot

No, not a diameter, not a scale. I talking about space between cut surface. Look now.

I will start on desk, yes, in normal size (1:1), but I will print plastic around.

Each blade which I mean to order wll be 20cm (two of them is cutting surface 40cm).

Question is how much this space must be? zero or minus ( - ) cm ?
Ask because if is zero, will be grass stay uncuted in middle?
(On this picture space is minus 1.5cm).