{
 "id": "38-coincident-cylinders",
 "name": "Union of coaxial equal cylinders",
 "description": "Cylinder r10 z 0..30 and cylinder r10 z 20..50 (coincident cylindrical faces), combine join.",
 "exercises": [
  "combine_join",
  "coincident_faces",
  "offset_plane"
 ],
 "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": "S1",
   "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": [
       0,
       0
      ]
     },
     "radius": 10,
     "id": "c1"
    }
   ],
   "constraints": [],
   "dimensions": []
  },
  {
   "op": "extrude",
   "name": "CylA",
   "operation": "new",
   "profiles": [
    {
     "sketch": "S1",
     "loops": [
      {
       "outer": true,
       "curves": [
        "c1"
       ]
      }
     ]
    }
   ],
   "extent": {
    "type": "distance",
    "distance": 30,
    "direction": "positive"
   },
   "result_bodies": [
    "A"
   ]
  },
  {
   "op": "construction_plane",
   "name": "Z20",
   "method": "offset",
   "base": "XY",
   "offset": 20
  },
  {
   "op": "sketch",
   "name": "S2",
   "plane": {
    "ref": "construction plane Z20",
    "origin": [
     0.0,
     0.0,
     20.0
    ],
    "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": [
       0,
       0
      ]
     },
     "radius": 10,
     "id": "c1"
    }
   ],
   "constraints": [],
   "dimensions": []
  },
  {
   "op": "extrude",
   "name": "CylB",
   "operation": "new",
   "profiles": [
    {
     "sketch": "S2",
     "loops": [
      {
       "outer": true,
       "curves": [
        "c1"
       ]
      }
     ]
    }
   ],
   "extent": {
    "type": "distance",
    "distance": 30,
    "direction": "positive"
   },
   "result_bodies": [
    "B"
   ]
  },
  {
   "op": "combine",
   "name": "Combine1",
   "operation": "join",
   "target_body": "A",
   "tool_bodies": [
    "B"
   ],
   "keep_tools": false
  }
 ]
}