Power Shelling
Power Shelling (Power Shell) enables the user to
offset, inset, and shell a open or
closed polysurfaces
in Rhino. Shelling enables the user to Preview the result
before
accepting it.
If the result is not what is desired the Wall
Thickness can be changed
or the operation can be Canceled. Shelling doesn't modify the original
object but
creates a new object. You may want to delete or hide the original object
after
shelling or offsetting.
Power Shelling Tip
- Don't shell objects with lots of NURBS fillets
(precise torii and cylindrical fillets are fine).
- Don't shell a NURBS surface with a radius so
large that it self-intersects unless it is a
precise extruded or revolved
NURBS surface.
- Don't expect Power Shelling to work on all
objects.
- You need to use the Offset - Extended
Surfaces option to offset polysurfaces that are not
closed (i.e. open shells).
Power Shelling Usage:
- To start the command either select "PowerShell"
from the menu or type "PowerShell" into the
Rhino command line.
- Pick a surface or polysurface.
- If doing a Hollow operation then pick one or
more shell faces.
- Type in the radius of the offset/inset/shell.
Note that positive and negative values are
acceptable. Negative values are interpreted as insets.
- Select the Operation Type:
- Hollow - Extended Surfaces this
operation does an offset/inset by extending
surfaces and computing new intersections at the extension. The
original object
is then subtracted from the result to give a hollowed out object with the
selected
shell faces being open.
- Offset - Extended Surfaces this
operation does an offset/inset by extending
surfaces and computing new intersections. The topology of the
resulting object
should be the same as the original (same number of edges, faces and
vertices).
This is the operation that should be used for non-closed objects, i.e. open
shells.
- Hollow - Rounded Corners does a
shelling operation and rounds convex edges
and corners. This operation also supports some difficult
self-intersection cases
but only works on closed solids.
- Offset - Rounded Corners does an
offset operation and rounds convex edges
and corners. This operation also supports some difficult
self-intersection cases
but only works on closed solids.
- Select the History option and then the OK
button.

Original Object

Power Shell Dialog Box. Note that you may
preview the results.

Here is a shell with a 0.2 radius offset and the front face selected as the
shell face.

Here is a shell with a -0.3 radius inset.

Offset (not shell) with a radius of 1.0.

Inset (not shell) with a radius of 0.2.

Lower Left Original Object. Lower Right is shell with surface extension.
Top images is
shell with rounded edges.
Offset Solids:
With version 2.0 of PowerShell, you can also
created Offset Solids. Offset Solids are basically
surfaces with a thickness. To create an Offset Solid, use the following
steps.
- Start the PowerShell command.
- Pick a surface or polysurface.
- Choose the "Hollow w/Extension"
option.
- Type in the value for the offset.
Note that positive and negative values are
acceptable. Negative values are interpreted as insets.
- Select the History option and then the OK
button.

Original surface (with no offset thickness).

PowerShell dialog box. Choose Hollow w/Extension option.

Offset Solid result. Notice thickness of object. A rotated version
of the object is shown below.
