Way to round edges of objects opensCAD

I was looking for a radiused block to 3d print an instrument case. After reading the earlier answers I looked into hull (Not the town! :-) making 8 identical spheres at the corners of a block and hulling them looks good.

module radiusedblock(xlen,ylen,zlen,radius){
hull(){
translate([radius,radius,radius]) sphere(r=radius);
translate([xlen + radius , radius , radius]) sphere(r=radius);
translate([radius , ylen + radius , radius]) sphere(r=radius);    
translate([xlen + radius , ylen + radius , radius]) sphere(r=radius);
translate([radius , radius , zlen + radius]) sphere(r=radius);
translate([xlen + radius , radius , zlen + radius]) sphere(r=radius);
translate([radius,ylen + radius,zlen + radius]) sphere(r=radius);
translate([xlen + radius,ylen + radius,zlen + radius]) sphere(r=radius);
       }
}
radiusedblock(30,40,50,5);

minkowski() is your friend for rounding over all edges of a geometry. minkowski() is also incredibly slow and should only be used for final rendering. You can also implement primitives which have rounded edges more efficiently with other constructs.

$fn=60;

module drawLedgeRing()
{
    difference()
    {
        cylinder(4,10,10);

        translate([0,0,-1])
        cylinder(4,6,6);

        translate([0,0,2])
        cylinder(4,8,8);
    }
}

minkowski()
{
    drawLedgeRing();
    sphere(.25);
}

//drawLedgeRing();

There are probably many ways to make a rounded cylinder. One way is to make 2 donut shaped objects and hull them

hull(){
rotate_extrude() translate([r1,0,0]) circle(r2);
rotate_extrude() translate([r1,0,h1]) circle(r2);
}