Printing Spheres

[curious aardvark]

couple of things that should make it easier.
You can use diameters instead of radii. This means that you don't have to mentally double the size of a sphere or cylinder every time you want one.
That and putting a module before you've defined it - make no sense to me :-)
I'm not a programmer, so a lot of the ways other people use openscad just strikes me as confusing and the wrong way round.
But that's the beauty of openscad - everyone can use it the way that makes sense to them.

Also for a rounder shape use a higher '$fn=' value.
I usually use the max: $fn-100;
Which gives you very round things. Takes a little longer to f6 render. But the models are better.

Another thing you can do is to use variables to create parametric objects.

$fn=100;

sd=10; //sphere diameter
wt=2; // thickness of sphere wall
hs=3; // hole size


difference() {
sphere(d=sd); //create sphere with diameter set by sd
sphere(d=sd-(2*wt)); //remove sphere from centre of original sphere - size defined by wt
translate([0,0,-sd/2])cylinder(d=hs,h=wt*4); // remove hole from bottom of sphere - diameter defined by hs
}

Because I used variables - whenever you change one of the numbers - the other automatically adapt.
Also for printing you want the sphere to be hole down.
The other thing that I find essential is to put a lot of coments into a script.
// can be put anywhere to write a comment to explain what you've done. Otherwise you'll come back to a script and it won't make any sense at all :-)
I know the maths can probably be improved - but the above script does work :-)