module base (R, X, theta, z) {

polyhedron(
	points = [
      [ 0,	0,	0],         // 0
      [   cos (theta) * X * R,
          sin (theta) * X * R, -z],  // 1
      [ R,      0,      -z],            // 2
      [   cos (theta) * X * R,
        - sin (theta) * X * R, -z],  // 3

      [ 0,	0,	        0],        // 4
      [   cos (theta) * X * R,		
        - sin (theta) * X * R,  z],         // 5
      [ R,      0,              z],         // 6
      [   cos (theta) * X * R,
          sin (theta) * X * R,  z],  // 7
      ],
      faces = [
      [0, 1, 2, 3, 0],
      [4, 5, 6, 7, 4],
      [0, 1, 7, 4],
      [1, 2, 6, 7],
      [3, 2, 6, 5],
      [0, 3, 5, 4],
       ]
);
}

delta_y =  5;   // step of vertical angle 
end     = 90;   // 

    R = 100 ;  // Radius
    X =  0.5;  // ratio outer:inner
theta = 40.0;  // center angle of 1/8 unit
    z = 0.1 ;  //  hull hackgin thickness

// base shape
module rotate_base( R, X, theta, i) {
    rotate([0, - i , 0]) base (R, X, theta * (1 - i/90), z);
}


module rough_shape (  delta_y, R, X ) {
// ----------------------------------
// repeat 8 times over horizontal plane
// ----------------------------------

   for ( angle = [0:45:315] ) {

       rotate([0, 0, angle]) 
        for ( i = [0:delta_y:end]) {
         hull(){
	    rotate_base( R, X, theta, i-5);
	    rotate_base( R, X, theta, i+5);
        }
    }
  }
}

outer_boundary = 1000;

intersection() {
   rough_shape ( delta_y, R, X );
     // to cut the small part below zero-height plane, prepare large box
   translate([0,0, outer_boundary/2])
   cube (size = outer_boundary, center=true);
}


basement_size = 500; // 500 um
thickness     = 1;   
  cube([ basement_size,   basement_size, thickness], center = true);