>>I don't understand why the primary edges for the facets do not run perpendicular to their associated surface edges.
Facet vertices are created along the underlying 2D parameter space grid for a face. From the image you attached, it looks like the face being faceted is an analytic face. An analytic planar face is defined by a point and normal plus boundary curves. Boundary curves have no effect on the parameterization and hence faceting. For some NURB faces such as a skin surface, the original edges do influence parameterization. Trim curves (cut outs,holes,etc) never influence parameterization and are typically defined by parameterization.
This is correct behavior for all ACIS based apps. I also believe true for ParaSolids and any kernel supporting analytic surfaces.
>>Their orientation is all over the place which I believe to be contributing to the corrupt STL export.
Can you provide and example of a corrupt TurboCAD STL file?
>>retained its previous values instead of reverting back to default each time
The Mesh Dialog shows you the settings of the selected object which is consistent with most dialogs. I believe you want to see the settings for the object you are seeing on the screen. If you select a solid, the dialog will show you the mesh settings related to the display list (SuperFine, Fine, Medium, etc) which is what you see on the screen. The display list only uses Normal Deviation where SuperFine = 5 degrees, and Fine = 12 degrees.
>>But a lower density is no good for printing.
My understanding is that you want a mesh model that represents the analytic/NURB model to a given tolerance. Normal Deviation and Surface Deviation are two excellent parameters. Normal Deviation is model size independent and will capture shape based on curvature. Surface Deviation will get those other instances where small changes over long spans that normal deviation might miss.
From the image you posted it looks like you have turned off Normal & Surface deviation in preference to only Edge Length. With this setting you might miss detail below the Edge Length plus add many facets to places not needed. For example, your planar faces may have more facets than needed to define the shape.
One other thing to note is that the 3D printer does not drive the print head from facets. It generates a 2D slice through the facets. So the only thing the facets are used for are creating a closed 2D region.
If you have a corrupt STL file I'd really like to see that and send off the to guys at Dassault. If you can send to IMSI tech support that would most appreciative! An easy check is to read the STL file back into TurboCAD. If the issue is not present, then it may be an issue with the other app reading the STL.
Hopes this helps clarify some of the meshing better!
TurboCAD Mac Development