Hi Dzeko,

> i think your cube is entierly cutted
>
> i more need this

For that type of case then yes you do need to do an extrusion.

You can do it in 2 different ways - if you want to do it like "push/pull", then you'd draw a rectangle on the front face of your box and use Edit > Trim to slice the surface of the box by that curve so that it's made of separate faces. Use Join if it split into totally separate objects. Then you can select the face and do Extrude and you'll get the auto boolean behavior as shown above.

The other way is to just extrude the curve to your desired cut size, then select the main object and run Construct > Boolean > Difference and select your just extruded piece as the cutting object.

In the future I do want to have the concept of a "depth limited" boolean so that you could control the cutting depth directly in the boolean command, but until that is ready you need to form your own cutting object by using Extrude.

- Michael