{
 "id": "66-sketch-linkage",
 "name": "Sketch solver: symmetric link",
 "description": "Link with R12 and R8 end arcs 60 apart joined by tangent lines, concentric d12/d8 holes, and two d4 holes symmetric about the construction centre line; fully constrained; extruded 6.",
 "exercises": [
  "sketch_only",
  "sketch_constraints",
  "tangent",
  "concentric",
  "symmetric",
  "offset_dim"
 ],
 "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": "Link",
   "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": "arc_three_point",
     "start": {
      "at": [
       2,
       11
      ]
     },
     "mid": [
      -13,
      1
     ],
     "end": {
      "at": [
       1,
       -12
      ]
     },
     "id": "a1"
    },
    {
     "type": "arc_three_point",
     "start": {
      "at": [
       58,
       -7
      ]
     },
     "mid": [
      69,
      1
     ],
     "end": {
      "at": [
       59,
       8
      ]
     },
     "id": "a2"
    },
    {
     "type": "line",
     "start": {
      "ref": "a2.end",
      "at": [
       59.0,
       8.0
      ]
     },
     "end": {
      "ref": "a1.start",
      "at": [
       2.0,
       11.0
      ]
     },
     "id": "l1"
    },
    {
     "type": "line",
     "start": {
      "ref": "a1.end",
      "at": [
       1.0,
       -12.0
      ]
     },
     "end": {
      "ref": "a2.start",
      "at": [
       58.0,
       -7.0
      ]
     },
     "id": "l2"
    },
    {
     "type": "line",
     "start": {
      "ref": "a1.center",
      "at": [
       -1.246268657,
       -0.380597015
      ]
     },
     "end": {
      "ref": "a2.center",
      "at": [
       61.079617834,
       0.328025478
      ]
     },
     "id": "lc",
     "construction": true
    },
    {
     "type": "circle",
     "center": {
      "ref": "a1.center",
      "at": [
       -1.246268657,
       -0.380597015
      ]
     },
     "radius": 5,
     "id": "h1"
    },
    {
     "type": "circle",
     "center": {
      "ref": "a2.center",
      "at": [
       61.079617834,
       0.328025478
      ]
     },
     "radius": 3.5,
     "id": "h2"
    },
    {
     "type": "circle",
     "center": {
      "at": [
       28,
       4
      ]
     },
     "radius": 2.5,
     "id": "h3"
    },
    {
     "type": "circle",
     "center": {
      "at": [
       31,
       -5
      ]
     },
     "radius": 1.5,
     "id": "h4"
    }
   ],
   "constraints": [
    {
     "type": "coincident",
     "refs": [
      "a1.center",
      "origin"
     ]
    },
    {
     "type": "horizontal",
     "refs": [
      "lc"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "l1",
      "a1"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "l1",
      "a2"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "l2",
      "a1"
     ]
    },
    {
     "type": "tangent",
     "refs": [
      "l2",
      "a2"
     ]
    },
    {
     "type": "symmetric",
     "refs": [
      "h3",
      "h4",
      "lc"
     ]
    }
   ],
   "dimensions": [
    {
     "type": "distance",
     "refs": [
      "a1.center",
      "a2.center"
     ],
     "value": 60,
     "unit": "mm",
     "orientation": "horizontal"
    },
    {
     "type": "radius",
     "refs": [
      "a1"
     ],
     "value": 12,
     "unit": "mm"
    },
    {
     "type": "radius",
     "refs": [
      "a2"
     ],
     "value": 8,
     "unit": "mm"
    },
    {
     "type": "diameter",
     "refs": [
      "h1"
     ],
     "value": 12,
     "unit": "mm"
    },
    {
     "type": "diameter",
     "refs": [
      "h2"
     ],
     "value": 8,
     "unit": "mm"
    },
    {
     "type": "diameter",
     "refs": [
      "h3"
     ],
     "value": 4,
     "unit": "mm"
    },
    {
     "type": "distance",
     "refs": [
      "a1.center",
      "h3.center"
     ],
     "value": 30,
     "unit": "mm",
     "orientation": "horizontal"
    },
    {
     "type": "offset",
     "refs": [
      "lc",
      "h3.center"
     ],
     "value": 4,
     "unit": "mm"
    }
   ]
  },
  {
   "op": "extrude",
   "name": "Extrude1",
   "operation": "new",
   "profiles": [
    {
     "sketch": "Link",
     "loops": [
      {
       "outer": true,
       "curves": [
        "a1",
        "a2",
        "l1",
        "l2"
       ]
      },
      {
       "outer": false,
       "curves": [
        "h1"
       ]
      },
      {
       "outer": false,
       "curves": [
        "h2"
       ]
      },
      {
       "outer": false,
       "curves": [
        "h3"
       ]
      },
      {
       "outer": false,
       "curves": [
        "h4"
       ]
      }
     ]
    }
   ],
   "extent": {
    "type": "distance",
    "distance": 6,
    "direction": "positive"
   },
   "result_bodies": [
    "Link"
   ]
  }
 ]
}