difference(){
cube([50,10,5], center=true);
for (i=[0:2:10]) {
-echo((4 + i/10));
-translate([(i-5)/2 * 7, 0, -7 ])
-cylinder(r= (4 + i/10)/2, h=14, $fn=10);
-}
+ sz = 4 + i/10;
+ echo(sz);
+ translate([(i-5)/2 * 7, 0, -7 ])
+ cylinder(r= sz/2, h=14, $fn=10);
+ }
}