Filleting and Projecting a 3d mesh

Hello forum.
I’m trying to create a profiled form (approximately shown in the photo of the wooden example).
I’m having difficulties 3 areas:

  • filleting a mesh
  • projecting an extrusion (up to a surface).
  • substracting one mesh from another.
    any pointers/support would be most welcome.
    Kind regards,
    Jason (28.9 KB)