mth= 1.16; //material. 
d= 6; //cut depth, 6 mm.
circle_R= 30;

difference (){
translate([0,0])
circle(circle_R);
translate([0,0])
circle(circle_R/3);
translate([circle_R,0])
circle(circle_R/4);
translate([-circle_R,0])
circle(circle_R/4); 
translate([0,-circle_R])
circle(circle_R/4); 
translate([0,circle_R])
circle(circle_R/4); 
translate([0-(mth/2),((circle_R)-(circle_R/4)-d+0.35)])
square([mth,d]);
translate([0-(mth/2),((-circle_R)+(circle_R/4)-0.35)])
square([mth,d]);
translate([((-circle_R)+(circle_R/4)-0.35),0-(mth/2)])
square([d,mth]);
translate([((circle_R)-(circle_R/4)-d+0.35),0-(mth/2)])
square([d,mth]);
translate ([(circle_R/2)+1.95,(circle_R/2)+1.95])
rotate(-45)
square ([mth,d]);
translate ([(-circle_R)+d+2.8,(-circle_R)+d+2.8])
rotate(-45)
square ([mth,d]);
translate ([(-circle_R)+d+7.05,(circle_R)-d-7.05])
rotate(45)
square ([mth,d]);
translate ([(circle_R/2)+6.2,(-circle_R/2)-6.2])
rotate(45)
square ([mth,d]);
}

translate ([35,0])
square ([5,27]);