When to use 'Support' option?

[terrypin]

"Your homework - make the box parametric :-)"

$fn=50;
// Defining the box
ExteriorL=100;  // Exterior cube, length
ExteriorW=40; // Exterior cube, width
ExteriorH=30; // Exterior cube, height

InteriorL=96; // Interior cube, length
InteriorW=36; // Interior cube, width
InteriorH=30; // Interior cube, height

// Hole making
SphereDiam=5;
CylDiam=10.4;
CylHeight=3.25;

difference(){
union(){
difference(){
cube([ExteriorL,ExteriorW,ExteriorH],true);
translate([0,0,2])cube([InteriorL,InteriorW,InteriorH],true);
} // end diff

translate([40,18,0]) resize([14,8,14])sphere(d=SphereDiam);
translate([-40,18,0]) resize([14,8,14])sphere(d=SphereDiam);
} // end union

translate([40,20,0]) rotate([90,0,0]) cylinder(d=CylDiam, h=CylHeight);
translate([-40,20,0]) rotate([90,0,0]) cylinder(d=CylDiam, h=CylHeight);
translate([0,30,0]) cube([100,20,30],true);
} // end diff

The only parameters I didn't define were those for what I think of as your 'third cube'. That's your homework! ;-)

11-CA-MagnetsInBox-Param.jpg

(This web site has possibly the most buggy formatting/rendering I've ever seen!)