Hi Andrei, at first I thought you'd just make a large 3 sided cutting surface and slice the full object with that.

But it looks like you want to have a controlled strip that comes more from a chamfer, but only a portion of the chamfer. So probably what I'd do in that case would be to do an actual chamfer, then select the chamfer face and do Ctrl+C to copy it to the clipboard temporarily. Now undo to go back to your original shape and Ctrl+V paste in the chamfer face.

Now slice the chamfer face using Trim with the "Isocurve" option to extract out just the region of the chamfer you want to keep.

Now draw lines from the end of the chamfer piece onto the main shape's edge, you now have 3 sided areas to fill in with Construct > Planar, join the chamfer and the 2 triangle pieces together to make your cutting surface and then use boolean difference to slice the main object with that as the cutting object (or use Trim).

Let me know if you are stuck on any of these steps.

- Michael