Bevel rectangle and boxes for OpenSCAD

bevel-box.scad

module bevel_rectangle(size, bevel) {
  s = (size[0] + size[1] - 2 * bevel) / sqrt(2);
  
  intersection() {
    square(size, center = true);
    rotate(45)
      square([s, s], center = true);
  }
}

module octahedron() {
  X = [1, 0, 0];
  Y = [0, 1, 0];
  Z = [0, 0, 1];
  
  polyhedron(
    points = [X, Y, Z, -X, -Y, -Z],
    faces = [
      [1, 0, 2],
      [0, 1, 5],
      [0, 4, 2],
      [4, 0, 5],
      [4, 3, 2],
      [3, 4, 5],
      [3, 1, 2],
      [1, 3, 5]  
    ],
    convexity = 2);
}

module bevel_box(size, bevel) {
  s = (size[0] + size[1] + size[2]) / 2 - 2 * bevel;
  sz = (size[0] + size[1] - 2 * bevel) / sqrt(2);
  sx = (size[1] + size[2] - 2 * bevel) / sqrt(2);
  sy = (size[2] + size[0] - 2 * bevel) / sqrt(2);
  
  intersection() {
    cube(size, center = true);
    rotate(45, [0, 0, 1])
      cube([sz, sz, size[2]], center = true);
    rotate(45, [1, 0, 0])
      cube([size[0], sx, sx], center = true);
    rotate(45, [0, 1, 0])
      cube([sy, size[1], sy], center = true);    
    scale(s)
      octahedron();
  }
}