//this module creates a 3D line. Essentially it is an elongated 3D polygon
module line3D(p1, p2, thickness, fn = 24) {
    $fn = fn;

//hull is a 3D transformation in OpenSCAD which combines multiple modules into one nice cover. https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Transformations#hull
    hull() {
        translate(p1) sphere(thickness / 2);
        translate(p2) sphere(thickness / 2);
    }
}

//this module utilizes 3D line iterative to generate a locus of 3D lines which accumulatively gives the resemblance of a 3D Spiral.
module polyline3D(points, thickness, fn) {
    module polyline3D_inner(points, index) {
        if(index < len(points)) {
            line3D(points[index - 1], points[index], thickness, fn);
            polyline3D_inner(points, index + 1);
        }
    }
    polyline3D_inner(points, 1);
}

//Spiral parameters, i.e. thickness, radius, how many layers
r = 8; 
h = 20; 
fa = 15;
circles = 1;

//locus of points which are used in Hull transformation to create a 3D line using the line3D module mentioned above
points = [
    for(a = [0:fa:360 * circles]) 
        [r * cos(a), r * sin(a), h / (360 / fa) * (a / fa)]
];
   


difference(){//subtracting spiral from a cylinder using difference operator
    cylinder(20,10 ,10);  //Solid sylinder
    polyline3D(points, 3, 3); // 3D spiral
}