After using a Knife Project tool check the Cut Trough checkbox in the Tool Shelf (T).
If you place the cutting object on the 'clean' face it'll make the hole. If the cutting object is placed so it's overlaping the edges of the cuted object it'll create a geometry (edges) on it (as @lemon mentioned in his comment).
After using a Knife Project tool check the Cut Trough checkbox in the Tool Shelf (T).
After using a Knife Project tool check the Cut Trough checkbox in the Tool Shelf (T).
If you place the cutting object on the 'clean' face it'll make the hole. If the cutting object is placed so it's overlaping the edges of the cuted object it'll create a geometry (edges) on it (as @lemon mentioned in his comment).
After using a Knife Project tool check the Cut Trough checkbox in the Tool Shelf (T).
