Hello
I am having no end of trouble getting these 2 parts to union

They are both solids, but every time I try to merge them I get a joined SRF with no obvious flaws. When I try to expose naked edges nothing shows up. I have tried to accomplish this many different ways and always get the same result. What rules am I breaking?
I appreciate any input!

""""""""""""""""What rules am I breaking?"""""""""""""""
Here's the one...

You seem to be correct, thanks for the tip.
I am figuring out 3d modeling as I go, so please excuse any stupid questions. Why cant MOI make that shape? I could make it with a mill, 3d printer, or by gluing 2 pieces of material together.

Hi Sean, that's called a non-manifold juncture and yes you generally need to avoid that in many CAD programs. Solids in MoI are expecting to have an outer skin where each edge is joined between 2 surfaces. A juncture like that would break this rule, you'd have more than 2 surfaces trying to share a single edge.

> I could make it with a mill, 3d printer, or by gluing 2 pieces of material together.

Often times they won't be able to be 3d printed either. But none of this really makes any difference, non-manifold junctures just add a lot of complexity to CAD calculations. They can be ok to be present temporarily during some early stages of the boolean calculation, just as long as the final results are able to be sorted into volumes that do not have any self intersections. A non-manifold area of a single volume is basically a type of self intersection.

- Michael

""""""I can make it with a mill or 3d printer""""""

Not really. In the real world, there would either be "some amount of material there" or "no material there and some amount of gap"....

In the real world, there is no such thing as "just a surface"...

So, you could either cut a very small gap in that corner, or fill in the corner with a very small volume. Both could be not really noticable to the eye

Hello Michael,

I thought that solid++ uses the Radial Edge Datastructure by Kevin Weiler. Am I wrong? Or is it used only internally to keep compatibility with other systems?

Have a nice day
Karsten

Hi Karsten, yes that's true that Solids++ is able to represent a non-manifold edge if desired and things like the booleans will use that during part of its data processing, but after the boolean calculation is completed MoI will decompose objects into manifold volumes and only put manifold objects into its own geometry database.

There are a lot of various difficulties with trying to work with non-manifold structures as a regular runtime object representation, things like import/export to other CAD systems, and other operations like filleting are not expecting to work with them.

- Michael