Creating Helical Surfaces

This task shows how to create helical surfaces from wireframe geometry.

The command Helix creates a helical surface, by gradually displacing the guide along the rotation axis at the same time as it rotates about this axis. The resulting surface is referred to as a helicoid.

Open the Helix.CATPart document.

  1. Click the Helix icon .
    The Helix Surface Definition dialog box appears.
 
 

The model contains 3 geometry elements.
 

  1. Select the Guide, the Starting Point and the Direction (axis of rotation).

  2. Set start angle to 0° and end angle to 90°.

  3. Set length to 0 mm.

  4. Click Apply.
  A Helix Feature surface is created.
 
 

Start and end angle as well as the pitch can be modified dynamically using the manipulators.

  1. Select the manipulators for start and end angle and modify the angles.
 
 

  1. Select the manipulator for pitch position and draw it along the axis of rotation.
 

By default, the input range for start and end angle is from 0° to 360°. This range can be modfied:
 

  1. Activate the context menu by clicking the right mouse button on the text field End and the option Range > Edit....
 
 

  1. Set in the dialog box 'Range' the Sup. Range to 720° and close the window with OK.
 
 

  1. Set in the dialog box 'Helix' the start angle to 0° and the end angle to 450 °.

  2. Click OK to create the helical surface.
You can define the following options:
  • Guide: Selection of the guide.
  • Starting Point: Selection of the origin of the local coordinate system.
  • Direction: Selection of the axis of rotation.
  Options tab
 
  • Rotation: The helical surface is defined by start and end angle by which the guide is rotated about the axis of rotation.
    • Start: Angle where the surface starts with reference to the starting point.
    • End: Angle where the surface starts with reference to the starting point.
    • Close: Equivalent with Start = 0° and End = 360°.
      The surface is closed if Pitch - Length = 0 mm and Angle = 0°.
  • Pitch: Height of the helix measured over an angle of 360° (not the height of the created helix). The turn spacing is the distance between the start and end points of the displacement along the axis after one complete revolution (angle of rotation 360°). It can be defined in millimeters (Length) or degrees (Angle).
    • Length: length = 2 x Pi x radius x tan(angle).
    • Angle: tan(angle) = length / (2 x Pi x radius).
  See Approximation tab
  See Output tab
  Click onto the 'More Info' button to display deviations and output results.
 
  • Display: Depending on the options selected, values are displayed in the graphics area.
  • Deviation: Maximum deviation between the edges of the created surface and the original curves.
    • Guide: Displays the deviation of the approximated guide.
    • Form: Displays the deviation from the helix surface.
  • UV: Display of the UV vectors of curves and surfaces.
  • Output Result: See Output Result
      

Contextual Menus
 

By clicking the manipulators Start and End angle with the right mouse button the following contextual menu is displayed:
 
 

Edit Angle
 

The Edit Angle option displays the Angle Tuner dialog box where you can specify a new angle value.
 
 

By clicking the manipulator Pitch position with the right mouse button the following contextual menu is displayed:

  • Edit Position: Change offset vector position.
  • Edit Length: Change offset distance.
  • Keep Point: Create the point at the picked location.
  • Invert: Invert offset direction.