{
 "id": "49-helical-sweep",
 "name": "Helical sweep (spline helix)",
 "description": "d4 circle swept along a 3-turn helix (R20, pitch 8) given as a fitted 3D spline through 12 points per turn; replayed as the true helix.",
 "exercises": [
  "sweep",
  "spline_3d",
  "helix"
 ],
 "units": {
  "length": "mm",
  "angle": "deg",
  "area": "mm2",
  "volume": "mm3"
 },
 "conventions": {
  "world": "right-handed; Z up. XY/XZ/YZ are the origin planes.",
  "sketch_frame": "sketch-local 2D coords; world = plane.origin + x*plane.x_dir + y*plane.y_dir (origin in mm). Profile 'loops' list sketch entity ids.",
  "point_refs": "'<id>.start' / '<id>.end' / '<id>.center' reuse (share) that existing sketch point; 'at' is its position when referenced.",
  "extrude_direction": "positive = along sketch plane normal unless stated",
  "selections": "selected faces/edges carry 'point': a world-space point on the face / the edge's parametric midpoint; pick the nearest face/edge to it."
 },
 "parameters": [],
 "features": [
  {
   "op": "sketch",
   "name": "Helix",
   "plane": {
    "ref": "XY",
    "origin": [
     0.0,
     0.0,
     0.0
    ],
    "x_dir": [
     1.0,
     0.0,
     0.0
    ],
    "y_dir": [
     0.0,
     1.0,
     0.0
    ],
    "normal": [
     0.0,
     0.0,
     1.0
    ]
   },
   "entities": [
    {
     "type": "fitted_spline",
     "fit_points": [
      [
       20.0,
       0.0,
       0.0
      ],
      [
       17.320508076,
       10.0,
       0.666666667
      ],
      [
       10.0,
       17.320508076,
       1.333333333
      ],
      [
       0.0,
       20.0,
       2.0
      ],
      [
       -10.0,
       17.320508076,
       2.666666667
      ],
      [
       -17.320508076,
       10.0,
       3.333333333
      ],
      [
       -20.0,
       0.0,
       4.0
      ],
      [
       -17.320508076,
       -10.0,
       4.666666667
      ],
      [
       -10.0,
       -17.320508076,
       5.333333333
      ],
      [
       -0.0,
       -20.0,
       6.0
      ],
      [
       10.0,
       -17.320508076,
       6.666666667
      ],
      [
       17.320508076,
       -10.0,
       7.333333333
      ],
      [
       20.0,
       -0.0,
       8.0
      ],
      [
       17.320508076,
       10.0,
       8.666666667
      ],
      [
       10.0,
       17.320508076,
       9.333333333
      ],
      [
       0.0,
       20.0,
       10.0
      ],
      [
       -10.0,
       17.320508076,
       10.666666667
      ],
      [
       -17.320508076,
       10.0,
       11.333333333
      ],
      [
       -20.0,
       0.0,
       12.0
      ],
      [
       -17.320508076,
       -10.0,
       12.666666667
      ],
      [
       -10.0,
       -17.320508076,
       13.333333333
      ],
      [
       -0.0,
       -20.0,
       14.0
      ],
      [
       10.0,
       -17.320508076,
       14.666666667
      ],
      [
       17.320508076,
       -10.0,
       15.333333333
      ],
      [
       20.0,
       -0.0,
       16.0
      ],
      [
       17.320508076,
       10.0,
       16.666666667
      ],
      [
       10.0,
       17.320508076,
       17.333333333
      ],
      [
       0.0,
       20.0,
       18.0
      ],
      [
       -10.0,
       17.320508076,
       18.666666667
      ],
      [
       -17.320508076,
       10.0,
       19.333333333
      ],
      [
       -20.0,
       0.0,
       20.0
      ],
      [
       -17.320508076,
       -10.0,
       20.666666667
      ],
      [
       -10.0,
       -17.320508076,
       21.333333333
      ],
      [
       -0.0,
       -20.0,
       22.0
      ],
      [
       10.0,
       -17.320508076,
       22.666666667
      ],
      [
       17.320508076,
       -10.0,
       23.333333333
      ],
      [
       20.0,
       -0.0,
       24.0
      ]
     ],
     "id": "h1"
    }
   ],
   "constraints": [],
   "dimensions": []
  },
  {
   "op": "sketch",
   "name": "ProfileSketch",
   "plane": {
    "ref": "XZ",
    "origin": [
     0.0,
     0.0,
     0.0
    ],
    "x_dir": [
     1.0,
     0.0,
     0.0
    ],
    "y_dir": [
     0.0,
     0.0,
     -1.0
    ],
    "normal": [
     0.0,
     1.0,
     0.0
    ]
   },
   "entities": [
    {
     "type": "circle",
     "center": {
      "at": [
       20.0,
       0.0
      ]
     },
     "radius": 2,
     "id": "c1"
    }
   ],
   "constraints": [],
   "dimensions": []
  },
  {
   "op": "sweep",
   "name": "Sweep1",
   "operation": "new",
   "profile": {
    "sketch": "ProfileSketch",
    "loops": [
     {
      "outer": true,
      "curves": [
       "c1"
      ]
     }
    ]
   },
   "path": {
    "sketch": "Helix",
    "curves": [
     "h1"
    ],
    "chained": false
   },
   "orientation": "perpendicular",
   "result_bodies": [
    "Spring"
   ]
  }
 ]
}