That kind of structure with a larger number of surfaces all meeting together at shared points creates a lot of complications for both offsets and fillets.
For offsetting a surface into a solid, it usually works best if the surface is totally smooth throughout - otherwise the offset of a surface made up of sharp bits requires a bunch of extensions of the offset pieces in order to make them connect up with each other, and the offset engine in the geometry library that MoI uses does not know how to handle cases where one vertex in the base surface diverges into multiple vertices in the generated offset.
See here for some illustration of this:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1939.10
And some other discussion of problems with offset/shell:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1209.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=649.7
http://moi3d.com/forum/index.php?webtag=MOI&msg=133.11
So yeah unfortunately something with the kind of structure that you show there is not possible to offset well with MoI - the authors of the geometry library that MoI uses have said that they are working on improving the Offset function in it to handle cases like this but I'm not sure when that will be complete.
That increase in the number of edges also makes things difficult for filleting as well - it creates much more complex corner juncture areas when you have 7 or 8 surfaces meeting in a common corner area rather than 3 or 4 surfaces at each juncture area. A much more complex "corner patch" needs to be created.
Also it's difficult for the filleter to handle cases where 2 surfaces are at a shallow angle to one another, like when they are fairly close to being smooth to one another but actually creased by only a 10 degree angle or so - the fillet that would be created in such an area becomes very small and small slivery things do not go well with intersection calculations.
So in order to produce offsets or fillets on the kind of geometry you have there it basically won't work to do it all at once, you'll need to break that apart into individual surfaces, and then work on things at a surface level - the offset of an individual surface will work, and then you'll need to form the intersection between different pieces. Also if you have 2 individual surfaces you can select each surface and run fillet on that selection - that will perform a surface/surface fillet operation that can often generate a fillet surface where the edge-based one gets confused. But the surface/surface filleter only basically generates one fillet segment, it does not try to resolve juncture areas where multiple fillets come together, you would need to trim them and create the junctures yourself.
Really my best advice is to export such a shape into a different modeler that has more robust offsets and fillets that can probably handle that kind of geometry better - ViaCAD is an inexpensive option for that: http://www.punchcad.com/p-9-viacad-2d3d-v8.aspx
- Michael |
