{
 "id": "26-sketch-belt",
 "name": "Sketch solver: tangent lines between circles",
 "description": "Circles d40 at origin and d20 at 50 mm (horizontal), concentric d8 hole, two lines tangent to both. All profiles extruded 5 mm.",
 "exercises": [
  "sketch_only",
  "sketch_constraints",
  "tangent",
  "concentric",
  "point_on_curve"
 ],
 "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": "Belt",
   "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": "circle",
     "center": {
      "at": [
       2,
       -1
      ]
     },
     "radius": 18,
     "id": "c1"
    },
    {
     "type": "circle",
     "center": {
      "at": [
       45,
       3
      ]
     },
     "radius": 12,
     "id": "c2"
    },
    {
     "type": "circle",
     "center": {
      "at": [
       46,
       2
      ]
     },
     "radius": 5,
     "id": "c3"
    },
    {
     "type": "line",
     "start": {
      "at": [
       3,
       19
      ]
     },
     "end": {
      "at": [
       47,
       13
      ]
     },
     "id": "l1"
    },
    {
     "type": "line",
     "start": {
      "at": [
       1,
       -22
      ]
     },
     "end": {
      "at": [
       44,
       -8
      ]
     },
     "id": "l2"
    }
   ],
   "constraints": [
    {
     "type": "coincident",
     "refs": [
      "c1.center",
      "origin"
     ]
    },
    {
     "type": "horizontal_points",
     "refs": [
      "c1.center",
      "c2.center"
     ]
    },
    {
     "type": "concentric",
     "refs": [
      "c3",
      "c2"
     ]
    },
    {
     "type": "coincident",
     "refs": [
      "l1.start",
      "c1"
     ]
    },
    {
     "type": "coincident",
     "refs": [
      "l1.end",
      "c2"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "l1",
      "c1"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "l1",
      "c2"
     ]
    },
    {
     "type": "coincident",
     "refs": [
      "l2.start",
      "c1"
     ]
    },
    {
     "type": "coincident",
     "refs": [
      "l2.end",
      "c2"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "l2",
      "c1"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "l2",
      "c2"
     ]
    }
   ],
   "dimensions": [
    {
     "type": "diameter",
     "refs": [
      "c1"
     ],
     "value": 40,
     "unit": "mm"
    },
    {
     "type": "diameter",
     "refs": [
      "c2"
     ],
     "value": 20,
     "unit": "mm"
    },
    {
     "type": "diameter",
     "refs": [
      "c3"
     ],
     "value": 8,
     "unit": "mm"
    },
    {
     "type": "distance",
     "refs": [
      "c1.center",
      "c2.center"
     ],
     "value": 50,
     "unit": "mm",
     "orientation": "horizontal"
    }
   ]
  },
  {
   "op": "extrude",
   "name": "Extrude1",
   "operation": "new",
   "profiles": [
    {
     "sketch": "Belt",
     "loops": [
      {
       "outer": false,
       "curves": [
        "c3"
       ]
      },
      {
       "outer": true,
       "curves": [
        "c2",
        "c2"
       ]
      }
     ]
    },
    {
     "sketch": "Belt",
     "loops": [
      {
       "outer": true,
       "curves": [
        "c1",
        "c1"
       ]
      }
     ]
    },
    {
     "sketch": "Belt",
     "loops": [
      {
       "outer": true,
       "curves": [
        "c1",
        "c2",
        "l1",
        "l2"
       ]
      }
     ]
    }
   ],
   "extent": {
    "type": "distance",
    "distance": 5,
    "direction": "positive"
   },
   "result_bodies": [
    "Belt"
   ]
  }
 ]
}