Shell not exact?

 From:  Michael Gibson
5385.11 In reply to 5385.9 
Hi Rudl, can you please post the model file of the result from TurboCAD ?

Just looking at the screenshot you posted, that does not necessarily look like an error.

It is a normal consequence of offsetting that a combination of planes at various different angles to one another will not produce a single vertex in the output while maintaining the same other boundaries of the existing surfaces - in order to produce a single vertex in the result it would require the planes to be extended some distance on their sides.

This is due to the different sized gaps between the "natural offsets" of the surfaces, I was trying to show you that earlier in this thread with this message here:

So if you want a single vertex in the result, you'll probably need to construct the extended region yourself, it will be easiest to do that if you have some good starting geometry to work off of which the TC result that you show a screenshot of may well be.

Mathematically with constant thickness offsets being used, you can either have a result where each edge in the output tracks along the surface normal of the originating edge, which will produce a different edge structure in the result just like you see there in TC, _OR_ you can have the same vertex structure if the surfaces are extended by whatever amount necessary to their sides which means you will have a single vertex there but due to the extension the edges on the boundary areas will not track exactly along the surface normal from the original edges, those edges will be extended over to the side by some amount.

It seems that maybe you want both of those at the same time, but yes as far as I understand that's not mathematically possible, you can get either same topology with extension/displacement of the final edges, or edges following along the surface normal of the original but with a deviation in topology as you show in TC.

I guess maybe I would need to know more details about what you plan to do with the result of the object in order to be able to give you some tips on how to do it - do you need the "side walls" of the shell to be at a precise 90 degree angle to the originating surface? If so then the result from TC is what you want. Or do you want there to be the same vertex structure in the output but the "side wall" connecting the edge will flare out since there will be some material added to the offset in order to make the extended pieces connect up again in a single point?

- Michael