I needed to make the STL file 1 mm thicker from front to back.
The attached image shows what happened after I did the following:
(I'd have uploaded the TCW file, but it's 25 MB)
1. Imported hi-res STL original.
2. Drew two Arcs above and below the frame and Lofted them so that they created a front and rear boundary.
3. Copied the Loft forward and backward and Lofted each pair together so that the resulting solids overlapped the desired front and rear sections of the frame.
4. After converting Lofts to TCSurfaces, 3D Subtracted them from copies of the frame to make the front and rear sections.
5. Moved the rear section back 1 mm.
6. (Arduously) traced the edges of the front piece (outer frame and two lens holes) using 3D Polyline.
7. Copied the 3D Polyline and moved it back 1 mm.
8. Lofted the each 3D Polyline to its copy to create a 1 mm thick filler.
9. 3D Added the front, rear and filler sections together.
10. Converted to ACIS Solid.
11. Viewed in Dynamic Cut Plane (I should point out that saving as STL from either TCSurface or ACIS Solid and viewing with MeshLab also indicates the same error).
I'm wondering if this is caused by the order in which I select the 3D Polylines for Lofting, in part.
As it turns out, it is. The direction in which you draw the 3D Polyline around the boundary interacts with the order in which you select the 3D Polyline and its copy for Lofting (steps 6 &
Is there the means of flipping all the facets in a selected Loft? I doubt it, but there should be.