Modeling Create geometry Specify continuity on a Square or Rail surface > What if...?

Build primary surfaces that maintain continuity

How to use tools that create primary (slab) surfaces that maintain continuity with surrounding surfaces.

Set up the Rail surface tool

How to prepare your model and set the options to use the Rail surface tool.

Prepare to use the Rail surface tool

Create one or more generation curves. Generation curves define the profile of the surface as it is swept out along the rails. The generation curves should point in the same direction.
Create one or more rail curves. Rail curves define the path of the generation curve as it sweeps out the surface. The rail curves should point in the same direction.
Make sure the generation curves intersect the rail curves.
See Make curves intersect

Set up the Rail surface tool

The Surfaces > Swept surfaces > Rail surface tool has options that control how many Generation Curves and Rail Curves it expects.

You can open the tool's option box and change those options depending on how many curves you have whenever you use the tool.

Or, you can set up multiple custom versions of the tool on a shelf, corresponding to the different combinations of Generation Curves and Rail Curves options.

See Create custom tools

Custom versions of the Rail surface tool corresponding to the different Generation Curves and Rail Curves settings are included on the default shelves that ship with AliasStudio.

AliasStudio automatically assigns different icons to different custom versions of the Rail surface tool depending on how the Generation Curves and Rail Curves options are set.

Sweep generation curves along rail curves (Rail)

Create a surface by calculating the area swept out by a generation curve moving along one or more rail curves. You can use one generation curve or blend between two or more generation curves.

Create a surface

Choose Surfaces > Swept surfaces > Rail surface .
In the option window, set the number of Generation Curves and Rail Curves you have.
Click the generation curve or curves. To deselect a generation curve, click it again.
If you chose 2+ generation curves, click Go when you are finished selecting generation curves.
Click the rail curve or curves.

Maintain continuity with other surfaces

In the Rail Control window, use the pop-up menus next to the names of the generation and rail curves to choose what type of continuity you want along that edge.

What if...?

] I can't create a surface from my curves?

Make sure your curves intersect. If modifications to the boundary curves cause them to stop intersecting (while construction history is on), a small red and yellow arrow appears at that corner. Right mouse clicking on the arrow displays a bubble with an explanation of the problem.



See Make curves intersect.
The Rail Surface tool tests whether curves intersect within the Curve Fit Distance tolerance in Construction Options. To change the Curve Fit Distance option, choose Preferences > Construction options .
You can't create a surface along rail curves with sharp corners, CV multiplicity, or multi-knots. To remove multi-knots, turn on the Rebuild option for rail curves.

] The surface is created away from the rails?

It is the generation curve's pivot point that travels along the rail curve. If the pivot point is not on the generation curve, the new surface will be offset.

See Change an object's pivot point

] The resulting surface is too complex?

Turn on the Rebuild options for the curves used to create the surface.





Turn on the Explicit control option, then manually choose how many spans the surface may have and what degree it should be in the U and V directions.

] I want to change a rail surface after I've worked on other objects?

Choose Object edit > Query edit and click the surface.

See View and edit the construction history of an object

Create a spiral tube (coil)

Create a surface in the shape of a spiral tube (helix) in order to model objects such as appliance cords or springs.

First you need to model a spiral curve to act as a rail. You then place a small circle or other closed curve at the beginning of the spiral to act as the profile. Finally, you use Swept surface tools such as Extrude or Rail surface to produce the coil.

Create the spiral curve

Draw a straight line that has the height of the spiral.
From one end of this line, create another straight line, perpendicular to it. The length of this second line should equal the radius of the spiral.
Choose Surfaces > Swept surfaces > Rail surface -.
In the control window set both Generation Curves and Rail Curves to 1, and set Rotate Xform to an angle of 360 or more. 360 degrees will produce one coil, 720 degrees will produce two coils, etc.
Select the second curve as the Generation Curve and the first curve as the Rail Curve to create a spiral surface.
Choose Curve Edit > Create > Duplicate curve and select the outside edge of the surface.
Delete (or hide) the surface and keep only the curve.

Create the coil surface

Place a small closed curve (such as a circle) centered at the beginning of the spiral, and perpendicular to it.
Choose Surfaces > Swept surfaces > Extrude (with Style set to Tube) or Surfaces > Swept surfaces > Rail surface (with Generation Curves set to 1 and Rail Curves set to 1).
Select the small closed curve first, then the spiral curve.

Create a surface inside four boundary curves or corners (Square)

Use Square to create a surface by blending inward from a combination of four free curves and/or corners.

Create a surface

Choose Surfaces > Boundary Surfaces > Square .
Click the boundary curves, or snap corner locators to existing geometry, in clockwise or counter-clockwise order.

What combination of curves and corners can I use?

If you mix curves and corners, you must click the curves first.

After the surface appears, you can move a corner locator by dragging it.

What if...?

] I can't create a surface from my curves?

Make sure your curves intersect. If modifications to the boundary curves cause them to stop intersecting (while construction history is on), a small red and yellow arrow appears at that corner. Right mouse clicking on the arrow displays a bubble with an explanation of the problem.



See Make curves intersect.
The Square tool tests whether curves intersect within the Curve Fit Distance tolerance in Construction Options. To change the Curve Fit Distance option, choose Preferences > Construction options .
You can't create a surface inside boundary curves with sharp corners, CV multiplicity, or multi-knots. To remove multi-knots, turn on the Rebuild option for rail curves.

] The resulting surface is too complex?

Turn on the Rebuild options for the curves used to create the surface.





Turn on the Explicit control option, then manually choose how many spans the surface may have and what degree it should be in the U and V directions.

] I want to change a Square surface after I've worked on other objects?

Choose Object edit > Query edit and click the surface.

See View and edit the construction history of an object

Specify continuity on a Square or Rail surface

Use the continuity table in the option box of a high-quality surfacing tool to specify what level of continuity the surface should maintain with its neighbors.

Specify continuity

In the option window of the tool you used to create a surface, use the pop-up menus next to the names of the generation and rail curves to choose what type of continuity you want along that edge.

To open the option window for an existing surface, choose Object edit > Query edit and click the surface.

See View and edit the construction history of an object

Set a manual tangent angle along an edge

In the option window, set the continuity for the edge to Tangent Angle.
Use the tangent angle manipulator to set the angle.

How do I use the tangent angle manipulator?

Click an axis line to set the tangent angle to 0, 90, 180, or 270 degrees.
Click an arc, then drag left and right to change the angle value, or type a number to set the value exactly.
When you are finished, click Go.

What if...?

] I can't achieve the continuity I want?

Make sure you clicked an edge or isoparametric curve of the adjacent surface when you used the Rail surface tool, not a left over free curve you used to create the surface.
Turn on the Rebuild check box for the edge. This allows the tool to change the geometry of the edge as it attempts to achieve continuity.
Turn on the Explicit control option, then increase how many spans the surface may have. This allows the Rail Surface tool to add more spans to the surface to achieve better continuity.

] Certain types of continuity are not available in the pop-up menu for an edge?

Some continuity types (Tangent, Tangent Angle, Curvature) are only available on edges that are connected to surfaces.

If it looks like your new surface shares an edge with an existing surface, but the continuity choices are not available, it probably means you accidentally clicked a construction curve, not the edge of the existing surface.

To fix this, delete your new surface, then hide any construction curves that are "in the way" and re-create the surface.

] I want to change the continuity of a surface after I've worked on other objects?

See View and edit the construction history of an object