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Pipes and sweeps

A sweep moves a profile, a flat outline, along a path and keeps the surface it traces: a circle along a curve becomes a tube, a square along a polyline becomes a bar, the cross-section of a moulding along the outline of a room becomes the moulding. The path is a wire; the result is a solid when the profile is closed.

Here a circle swept along a helix makes a coil spring, and the same circle swept along a star whose corners are rounded first makes a smooth frame:

Bitbybit Platform

A spring and a star frame swept along wires in Rete

rete logoRete
Script Source (rete)
{
  "id": "rete-v2-json",
  "nodes": {
    "helix": {
      "id": "helix",
      "name": "bitbybit.occt.shapes.wire.createHelixWire",
      "customName": "create helix wire",
      "async": true,
      "drawable": true,
      "data": {
        "genericNodeData": {
          "hide": true,
          "oneOnOne": false,
          "flatten": 0,
          "forceExecution": false
        },
        "radius": 1.5,
        "pitch": 0.8,
        "height": 5,
        "center": [
          0,
          0,
          0
        ],
        "direction": [
          0,
          1,
          0
        ],
        "clockwise": false,
        "tolerance": 0.0001
      },
      "inputs": {},
      "position": [
        40,
        40
      ]
    },
    "spring": {
      "id": "spring",
      "name": "bitbybit.occt.operations.pipeWireCylindrical",
      "customName": "pipe wire cylindrical",
      "async": true,
      "drawable": true,
      "data": {
        "genericNodeData": {
          "hide": false,
          "oneOnOne": false,
          "flatten": 0,
          "forceExecution": false
        },
        "radius": 0.15,
        "makeSolid": true,
        "trihedronEnum": "isConstantNormal",
        "forceApproxC1": false
      },
      "inputs": {
        "shape": {
          "connections": [
            {
              "node": "helix",
              "output": "result",
              "data": {}
            }
          ]
        }
      },
      "position": [
        460,
        40
      ]
    },
    "star": {
      "id": "star",
      "name": "bitbybit.occt.shapes.wire.createStarWire",
      "customName": "star wire",
      "async": true,
      "drawable": true,
      "data": {
        "genericNodeData": {
          "hide": true,
          "oneOnOne": false,
          "flatten": 0,
          "forceExecution": false
        },
        "center": [
          6,
          0,
          0
        ],
        "direction": [
          0,
          1,
          0
        ],
        "numRays": 5,
        "outerRadius": 2.5,
        "innerRadius": 1.2,
        "offsetOuterEdges": 0,
        "half": false
      },
      "inputs": {},
      "position": [
        40,
        560
      ]
    },
    "rounded": {
      "id": "rounded",
      "name": "bitbybit.occt.fillets.fillet2d",
      "customName": "fillet 2d",
      "async": true,
      "drawable": true,
      "data": {
        "genericNodeData": {
          "hide": true,
          "oneOnOne": false,
          "flatten": 0,
          "forceExecution": false
        },
        "radius": 0.4
      },
      "inputs": {
        "shape": {
          "connections": [
            {
              "node": "star",
              "output": "result",
              "data": {}
            }
          ]
        }
      },
      "position": [
        460,
        560
      ]
    },
    "frame": {
      "id": "frame",
      "name": "bitbybit.occt.operations.pipeWireCylindrical",
      "customName": "pipe wire cylindrical",
      "async": true,
      "drawable": true,
      "data": {
        "genericNodeData": {
          "hide": false,
          "oneOnOne": false,
          "flatten": 0,
          "forceExecution": false
        },
        "radius": 0.2,
        "makeSolid": true,
        "trihedronEnum": "isConstantNormal",
        "forceApproxC1": false
      },
      "inputs": {
        "shape": {
          "connections": [
            {
              "node": "rounded",
              "output": "result",
              "data": {}
            }
          ]
        }
      },
      "position": [
        880,
        560
      ]
    }
  },
  "modules": {}
}

Tubes and bars, the profile made for you​

  • bitbybit.occt.operations.pipeWireCylindrical sweeps a circle of radius along a wire: a round tube, a cable, a handrail, a spring. pipeWiresCylindrical does the same for several wires at once.
  • bitbybit.occt.operations.pipePolylineWireNGon sweeps a regular polygon with nrCorners corners: a square bar with 4, a hexagonal one with 6.

Both take makeSolid (true for a solid, false for an open shell) and trihedronEnum, which decides how the profile turns as it travels. The default, isConstantNormal, keeps it steady; the Frenet modes turn it with the curve's bending, which can twist a profile along a path that bends one way and then the other.

Your own profile​

bitbybit.occt.operations.pipe takes the path as shape and one or more profiles as shapes. A profile is swept from where it stands and is not moved, so draw it across the start of the path, at a right angle to it. Several profiles, each placed where it belongs along the path, make the sweep blend from one shape into the next; the result is closed into a solid. pipeWithHistory does the same and reports which face each profile edge became, for selecting the caps or the sides afterwards.

Profiles that change on the way​

bitbybit.occt.operations.pipeWithScaling sweeps one profile along a spine and scales it as it goes: params are places along the spine from 0 at its start to 1 at its end, and scales the size of the profile at each, 1 being its own size. A tube that narrows toward one end takes params: [0, 1] and scales: [1, 0.5].

Mouldings along a flat outline​

bitbybit.occt.operations.sweepEvolved sweeps a profile along a flat spine and keeps it beside the spine rather than across it, the way a skirting board follows the walls of a room. The profile is drawn about the origin, with x along the spine, y to the left of travel and z up from the spine's plane; a closed spine gives a closed ring.

When a sweep fails​

  • The profile is wider than the path's tightest bend. A tube whose radius is larger than the radius of a curve folds over itself there. Use a smaller profile or a gentler path.
  • The profile is not at the start of the path. pipe sweeps the profile from where it is, so a profile drawn at the origin sweeps a shape somewhere else entirely.
  • The path has a sharp corner. A profile swept round a sharp corner of a polyline comes out kinked or broken at the corner. Round the corners first with bitbybit.occt.fillets.fillet2d, as the example does with the star, and forceApproxC1 smooths a tube that still came out with kinks.

Extrusions and lofts, the other ways to make a solid from outlines, are on Extrusions and Simple loft.