Here's an X shape formed by cutting some ellipses out of a cube.
I would like to smooth the sharp corners on the sides by subtracting
a shape that will be tangent to the side ellipsis and the side of
the cube, as per the red markup in the attached image.
How can I calculate that shape, or otherwise smooth the sharp edge?
// top and bottom
translate([WW/2,0,0]) scale([1,2.5 ,1]) cylinder(ZZ,d=WW-(10));
translate([WW/2,HH,0]) scale([1,2.5,1]) cylinder(ZZ,d=WW-(10));
translate([0,HH/2,0]) scale([1,1.8,1]) cylinder(ZZ,r=WW/4);
translate([WW,HH/2,0]) scale([1,1.8,1]) cylinder(ZZ,r=WW/4);
// smooth the arms