Once the surface based concept model is proven it needs to progress to a solid model with mass properties. Thicken and solidify are two tools which can create a closed (solid) volume from a construction (surface) feature.
Thicken
In a similar way to a Shell, offset surfaces can be created from a quilt and with the addition of ribbon side surfaces a solid is generated.
Also similar to the shell feature, the Thicken process will fail if there is geometry the system cannot resolve – small, narrow, high curvature surfaces are classics to fail.
Use the preview button to force the system to try and build the geometry, if elements fail it may then give you the option to exclude the failed surfaces which you can handle manually.
Options tab > Exclude Surfaces to deselect problem patches within the selected quilt.
For more special handling options on problematic quilts it may be worth using the Offset Surface tool
Solidify
The Solidify command will perform various operations dependent of the selected geometry.
A number of surfaces enclosing a volume can be used to form a solid – all the individual surfaces need to be merged as a quilt first. An ‘open’ surface volume can also be closed by the intersection of a solid which ‘closes’ the volume.
A surface can be used as a cutting plane through a solid – make sure you select the cut option in the dashboard.
1. the base curves of the top green surface must sit on or below the solid surface to create a closed (watertight/manifold) volume. The edges of the surface cutting the corner must be outside or on the solid surfaces – if any are inside it would be ambiguous what portion of the solid is to be sliced off.
2. the corner of the solid has been removed using the 
cut option in the dashboard – the surface extends outside the solid
3. if the edges of the ‘cutting’ surface are on the solid surfaces then the 
replace/patch option is used – basically does the same job as cut.
4. the surface intersecting the top of the solid creates a closed volume, the 
fill option is used to add this volume to the solid – notice the change in colour scheme.
Don’t work with bad geometry
If you start with messy geometry which has any sort of tight creases, folded self intersect quilts or a generally overly complex the are probably wasting your time trying to create a volume.
Always consider reworking the base geometry, in the example below the poor geometry needs cutting right back to some clean edges as the structure for some cleaner surfaces
Trimmed back and refilled
Replacing high curvature boundaries
If the above form is a small detail the G1 boundary can cause the offset/shell/thicken to fail. Relieve the curve end conditions and the surf boundary conditions and add fillets after creating the solid.
Work arounds where offset geometry fails
Make sure you recognise which are your A (outer significant surfaces), B (generally hidden but may be seen – undersides, inside lids and caps) or C (internal surfaces) surfaces. For a classic shelled part the offset (B/C) surfaces which form the wall thickness generally do not have to ‘replicate’ the A surfaces.
Different situations are going to require different versions of this work around, consider it generically.
In the above the scoop element of the surface will not thicken and has been excluded from the offset surface set. It doesn’t matter what the inner C surface looks like, it simply has to close the volume for the wall thickness.
A simple rectangular surface is created on the inner face surrounding the missing volume. As we have symmetry another surface is created to close the volume on the symmetry plane. The two new surface and the original un-thickened outer surface are merged, these now form a single quilt and ‘cap’ the solid.
Select the merge and solidify
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