od=60;  //diameter
n=13; //number of scallops

thickness = 10;
roundover =4 ; 

$fn=50;

ang = 360/n;
// chord  =   2*rt *sin(a/2) 

chord = od*sin (ang/2);  // == scallop diam

module shape(){
  difference(){
      circle (d=od);
        for (j= [0:ang:360])
         rotate([0,0,j])
         translate ([od/2,0,0])
         circle (d=chord);
   }
}

module finish(){
   minkowski(){
  linear_extrude(thickness -roundover*2)
  offset (r=-roundover)
  shape();
   sphere(4);
   }
} 
  
  intersection(){
     union(){ 
      finish();
       translate([0,0,6])
          scale([0.7,0.7,1]) 
         linear_extrude(8) shape();
    }
    translate([0,0,-85])
   # sphere(100);
    }
    
   translate([60,0,0]) cube(10);  //test