screw_util.scad

screw_util.scad

$fa = 24;
$fs = 0.1;


thread_profiles = [
  ["Tr", function (P) (
    let (H1 = 0.5 * P, H = P / (tan(15) * 2), _w1 = P / H * (H + H1) / 2, _w = P / H * (H - H1) / 2)
    [
      [[_w1 * 0.5, -H1], [_w * 0.5, 0], [_w * -0.5, 0], [_w1 * -0.5, -H1]], // ext
      [[_w1 * 0.5, -H1], [_w * 0.5, 0], [_w * -0.5, 0], [_w1 * -0.5, -H1]], // int
    ]
  )]
];

echo(thread_profiles[0][1](1.5));


function slice_points(D=8.0, P=1.5, rot=5, kind="ext", prof=thread_profiles[0][1]) = [
  // See: https://files.openscad.org/documentation/manual/Other_Language_Features.html#Special_variables
  let (
    fn = ( $fn > 0 ?
      ( $fn >= 3 ? $fn : 3 ) :
      ceil(max(min(360 / $fa, D * PI / $fs), 5))),
    _v = (kind == "ext" ? prof(P)[0] : prof(P)[1]),
    r = D / 2
  )
  for (n = [0 : ceil(fn * rot)]) 
  let (_dn = n / fn, _deg = 360 * _dn)
  for (p = _v)
  [cos(_deg) * (p[1] + r), sin(_deg) * (p[1] + r), P * _dn + p[0]]
];


shapes = slice_points();
_connections = [
  [4,5,1,0],
  [5,6,2,1],
  [6,7,3,2],
  [7,4,0,3]
];


faces = let (_nshapes = len(shapes), _last = _nshapes - 1) [
  [0, 1, 2, 3],
  for (n = [0 : 4 : _nshapes - 5])
  for (_v = _connections)
  [ for (i = _v) n + i ],
  [_last, _last - 1, _last - 2, _last - 3],
];

echo([ for (i = [0 : 7]) faces[i]]);

module screw_cylinder(D=8.0, P=1.5, rot=5, kind="ext", prof=thread_profiles[0][1]) {
  let (
    fn = ( $fn > 0 ?
      ( $fn >= 3 ? $fn : 3 ) :
      ceil(max(min(360 / $fa, D * PI / $fs), 5))),
    _v = (kind == "ext" ? prof(P)[0] : prof(P)[1]),
    d2 = D + min([ for (p = _v) p[1] ]) * 2
  )
  translate([0, 0, -P / 2]) cylinder(h = P * (rot + 1), d = d2);
}

union() {
polyhedron(shapes, faces);
screw_cylinder();
}