A suggestion of a solid with a square, hexagon, and circle orthogonal projections.

SquareHexagonCircle.scad

radius = 20;
hexradius = radius * cos(15);
intersection()
{
  translate([0,0,-radius])
  {
    linear_extrude(height=2*radius)
    {
      rotate([0,0,15])
      {
        polygon([
          [radius, 0],
          [radius * cos(60), radius * sin(60)],
          [radius * cos(120), radius * sin(120)],
          [radius * cos(180), radius * sin(180)],
          [radius * cos(240), radius * sin(240)],
          [radius * cos(300), radius * sin(300)]
        ]);
      }
    }
  }
  rotate([90,0,0])
  {
    translate([0,0,-radius])
    {
      cylinder(2*radius,hexradius,hexradius);
    }
  }

  rotate([0,90,0])
  {
    translate([0,0,-radius])
    {
      linear_extrude(height=2*radius)
      {
        polygon([
          [hexradius,0],
          [0,hexradius],
          [-hexradius,0],
          [0,-hexradius]
        ]);
      }
    }
  }
}