Guided loft: Create a surface using birails
Description: 5 minutes; Lab exercise: 20 minutes
Birail curves define the paths for the profiles to
follow and are interpolated by the created surfaces. Use birail curves to add
the surface to an existing part or to create a more complex shape.
When using birails, choose from four options:
- None - No scaling
is applied. The number of birails to be used is 1.
- Isotropic -
Scaling occurs in all directions within the profile plane and with respect to
the spine.
The number of
birails to be used is 1 or 2.
- Unidirectional -
Scaling occurs in a specific direction depending on the number of birails. The
number of birails to be used is 1 or 2.
- One birail - The direction is determined by the distance
between the spine positions and the corresponding positions on the birail.
- Two birails - The direction is determined by the two
points where the profile plane intersects the birails.
- Bidirectional -
Scaling occurs in two directions.
The first direction
is determined by the normal field, chosen by the Orientation Option. For each
point on the spine, the normal field defines a direction that is orthogonal to
the spine tangent at this point. The second direction is orthogonal to the
first direction and lies within the profile plane. The number of birails to be
used is 2.
Conditions for birails
Limitations
- Birails are not supported if the profiles are not planar
or orthogonal to the spine.
- Birails cannot be used to create a surface with a
tangential connection to existing surfaces.
For more about using birails, see
Guided loft: Create a surface
using unidirectional scaling.
Lab exercise
Prerequisites
Using one birail
- Load the
vase.pkg file.
- Click Surfacing
.
- Click Guided Loft
in the Create Face section.
- Select the straight line as the
Spine.
- Select the circle as the
Profile Edges (two curves).
- Select the curve as the
Birail Edges. The Isotropic
option is on by default.

-
Click Preview.

-
Click
to complete the operation.
Because there were two profile edges that made up
the circular profile, the resulting vase has two surfaces.

Try this lab again by changing the scaling options
to None and Unidirectional. Bidirectional will not work because there is only
one birail.
 Birail Scale: None |
 Birail Scale:
Unidirectional |
Using two birails
- Load the
bidirectionalscalingwithbirails.pkg file.
- Click Surfacing
.
- Click Guided Loft
in the Create Face section.
- Select the straight line as the
Spine.
- Select the two circles as the
Profile Edges (two curves).
- Select the two curves as the
Birail Edges. The
Isotropic option is on by default.
- Click Preview and
view the model from the top (Z direction).
This will give you
the best view of how the shape changes according to the birail scaling option
you choose.
- Choose an option and click
to finish.
Integrate a surface
Birails can be used to integrate a surface into a given model. The profiles
are translated, rotated, and scaled in order to make the surface fit to the
birail curves.
- Load the
twobirailsforpartintegration.pkg file.
- Click Surfacing
.
- Click Guided Loft
in the Create Face section.
- Select the straight line as the
Spine.
- Select the both ends of the model as the
Profile Edges.
- Select the top and bottom of the empty space as the
Birail Edges. The
Isotropic option is on by
default.
- Click
to
integrate the guided loft surface into the existing surface.