Create smooth curves that run along a face or surface in the U or V direction.

Similar to a weave of cloth, every surface is roughly rectangular. Surfaces have three directions: U, V, and Normal. The Boundary surface profiles U and V represent the X and Y directions of the surface, respectively.

Isoparametric curve created along a smooth surface

Use these curves with other features. For example, you can split the face using the curves. Then, use the Delete Face feature to remove the center portion. Once removed, you can add a ruled surface, 3D Fit splines, and Loft.

Isoparametric curves are smooth curves that run along a face or surface in the U or V direction. The Isoparametric curve feature adds selectable curve entities to the Part Studio for reference in other features.

Start a new isoparametric curve feature. Select a face to apply the curves to. The face can be on a solid body or surface. The Direction dropdown allows you to select either the U or V direction to place the curves. The Equal spacing checkbox changes how the location of the curves along the surface are defined. To specify a number of evenly spaced curves along the face, check Equal spacing and input an Instance count.

To create curves based on position, leave Equal spacing unchecked. Inside the Positions group box, click Add Curve. Set a Location or select a point to place the curve. Location is relative to the selected face, represented as a percentage. Input a value between 0 and 1. A value of 0.5 places the curve at the center of the face. Check Select point and pick a point, vertex, or explicit mate connector. Optionally, add an implicit mate connector by selecting the Mate connector icon to the right of the field.

To add additional curves, click Add Curve and repeat the process. Click X to remove a single curve or Clear to remove all curves. Once placed, accept the feature.

Use these curves with other features. For example, split the face using the curves. Then, use the Delete Face feature to remove the center portion. Once removed, add a ruled surface, two 3D fit splines, and finish with a loft.

With at least one face or surface in the graphics area:

  1. Click Isoparametric curve icon.

    Isoparametric curve dialog

  2. With focus in the Select face field, click the face(s) and/or surface(s) on which to create the curve.
  3. Select a direction:
    1. U direction - Curves will run in the X direction of the surface.

      Isoparametric curve in U direction with equal spacing

    2. V direction - Curves will run in the Y direction of the surface.

      Isoparametric curve in V direction with equal spacing

  4. Select the location for the curves:
    • To place a set number of equally spaced curves:
      1. Check the Equal spacing option.
      2. Enter the number of curves in the Instance count field.

      Isoparametric curve in V direction with equal spacing

    • To specify a precise location for a curve:
      1. Uncheck the Equal spacing option.
      2. Click Add Curve.
      3. Input a value between 0 and 1 in the Location field. The Location is relative to the selected face, so a value of 0.5 places the curve at the face's center.

      Isoparametric curve in V direction with equal spacing

    • To choose a sketch point as the curve location:
      1. Uncheck the Equal spacing option.
      2. Click Add Curve,
      3. With focus in the Select point field, click a sketch point in the graphics area.

      Isoparametric curve in V direction with equal spacing

    • To choose a mate connector as the curve location:
      1. Uncheck the Equal spacing option.
      2. Click Add Curve,
      3. Click the Mate connector icon.
      4. Select a Mate connector in the graphics area.
      5. Optionally, click the Mate connector in the Select point field to open the Mate connector dialog. Edit the Mate connector as needed, then close the Mate connector dialog.

      Isoparametric curve in V direction with equal spacing

  5. Click Accept checkmark icon to accept.

  • Click the X in the Position field to remove a defined curve.

  • Click CLEAR in the Position field to remove all defined curves.

  • The numeric fields in the Isoparametric curve dialog have slightly different keyboard+scroll shortcuts than other Onshape dialogs.

    Isoparametric Curve Dialog
    Scroll+Key Result
    Scroll wheel default Increments of 1.0
    Ctrl+scroll wheel Increments of 0.01
    Shift+scroll wheel No effect

In addition to the surfacing tools, curves are used to create the basic building blocks of surfaces.

This lists the collection of curve feature tools. This is not an exhaustive list. Additional Feature tools may be used when manipulating curves.

  • Sketch tools - Tools in the Sketch toolbar such as Line, Corner rectangle, Center point rectangle, Center point circle, 3 point circle, Tangent arc, 3 point arc, Spline, Point, and Construction used to create a sketch in a Part Studio.
  • Helix - Create a helix using a conical or cylindrical face, single axis or z-axis of a mate connector, or circular edge.
  • 3D fit spline - Create a 3D fit spline through a series of vertices. Creates a curve which is listed in the Parts list under Curves.
  • Projected curve - Create a curve from the projection of two sketches (Two sketches option) or from the projection of a curve on a face (Curve to face option).
  • Bridging curve - Create a Curve connecting any two points, vertices, or Mate connectors. The resulting Curve is listed in the Feature list and the Parts list.
  • Composite curve - Represent multiple edges as one Curve. Select multiple adjacent edges, sketch entities, and other curves. Selecting non-contiguous edges may result in multiple Curves created. Selections for each Curve must meet at their vertices. (Curves are listed in the Parts > Curves list.)
  • Intersection curve - Create a curve at the intersection of two or more surfaces or faces. The selections must intersect.
  • Trim curve - Trim or extend a curve by a distance or to a bounding entity.
  • Isocline - Create an isocline on a sloped face. An isocline runs on a face at positions where the face has a certain slope compared to its reference definition. The resulting isocline is listed in the Feature list and Parts list.
  • Offset curve - Create and extend and/or split a new curve by offsetting edges on surrounding faces.
  • Isoparametric curve - Create smooth curves that run along a face or surface in the U or V direction.
  • Edit curve - Edit an existing curve by selecting sketch entities or curves to apply a simplified approximation, elevate the degree, reposition control curve vertices and/or planarize into any 2D plane.

iOS and Android support for the Isoparametric curve feature is limited to displaying and editing existing curves. Isoparametric curves can only be created on the desktop (browser) platform. They cannot be created on iOS or Android platforms.