//knob parameters
KNOB_HEIGHT=10;
KNOB_DIAM=30;

//screw parameters
SCREWHEAD_FACETOFACE=11;
SCREWHEAD_DEPTH=8;
THRU_HOLE_DIAM=0;

//grippy cutouts parameters
NUM_GRIP_CUTOUTS=16;
GRIP_CUTOUT_DIAM=4;
CUTOUT_RADIUS_ADJ=1;

module FaceToFaceHex(width,height){
    cube([width/sqrt(3),width,height],center = true,$fn=64);
    rotate([0,0,120])cube([width/sqrt(3),width,height],center = true);
    rotate([0,0,240])cube([width/sqrt(3),width,height],center = true);

}
// a=angle, r=radius of rotation
module rotate_on_circle(angle, radius) {
    dx=radius*sin(angle);
    dy=radius*cos(angle);
    translate([dx,dy,0])
    children();   
}

difference(){
    //Knob
    union(){
        translate([0, 0, -(((KNOB_HEIGHT-SCREWHEAD_DEPTH)/2)+0.01)]) 
        cylinder(r=KNOB_DIAM/2, h=KNOB_HEIGHT, center=true,$fn=64);
        translate([0, 0, -(((KNOB_HEIGHT-SCREWHEAD_DEPTH+KNOB_HEIGHT)/2))]) {
        * cylinder(r=KNOB_DIAM/4, h=KNOB_HEIGHT/2, center=true,$fn=64);
        }
    };

    //screw
    union(){
        //screwHead
        FaceToFaceHex(SCREWHEAD_FACETOFACE,SCREWHEAD_DEPTH);
        //screwHole
        translate([0, 0, -(((KNOB_HEIGHT+SCREWHEAD_DEPTH)/2)+0.001)]) 
        cylinder(r=THRU_HOLE_DIAM/2, h=KNOB_HEIGHT+KNOB_HEIGHT/2+0.001, center=true,$fn=64);
    };

    //grippyCutouts
    for(i=[1:NUM_GRIP_CUTOUTS]){
        rot_angle=(360/NUM_GRIP_CUTOUTS)*i;
        translate([0,0,-(((KNOB_HEIGHT-SCREWHEAD_DEPTH)/2)+0.01)])
        rotate_on_circle(rot_angle,(KNOB_DIAM/2)+CUTOUT_RADIUS_ADJ)
        cylinder(r=GRIP_CUTOUT_DIAM/2,h=KNOB_HEIGHT+0.01,center=true,$fn=64);
    };
        
    //top filet
    translate([0, 0,-(((KNOB_HEIGHT-SCREWHEAD_DEPTH)/2)-0.1)])
    rotate_extrude()
        polygon(points = [[KNOB_DIAM,KNOB_HEIGHT], [0,KNOB_HEIGHT+2],[0,KNOB_HEIGHT],[KNOB_DIAM/1.29,0]],$fn=100);
    //down filet
    color("pink") {
        translate([0, 0,-(((KNOB_HEIGHT-SCREWHEAD_DEPTH)/2)+0.1)])
        rotate_extrude()
        polygon(points = [[-KNOB_DIAM,-KNOB_HEIGHT], [0,-KNOB_HEIGHT-2],[0,-KNOB_HEIGHT],[-KNOB_DIAM/1.29,0]],$fn=100);
    }
}