Can't combine bodies and thicken some surfaces

[marcocipriani01]

I created two bodies, but I can't find a way to combine them. The yellow body is the result of several operations with surfaces, which I eventually turned into a body with the Stitch command. Both bodies are watertight (otherwise they wouldn't even be bodies, I guess). The bottom face of the yellow body is perfectly flat, as the top face of green body.

I attached the Fusion design, in which I unfortunately had to turn the bodies into a Base Feature and delete everything else in the design, since it's a work design I can't share directly. The error is present even in this simplified design, however.

Can someone explain why I can't combine these two bodies?

I think it's some kind of bug, because if I convert both bodies to meshes, Fusion lets me combine the meshes without issues. This tells me that the geometries are valid and the bodies are actually watertight, as Fusion would fail to convert to meshes otherwise.

[jeff_strater]

I believe the problem is in the larger, yellow body.  It fails a model checker utility.  I'm not sure exactly what the error means, but I do notice that this body has massive tolerant edges on it.  Using an internal tool that visualizes the tolerant edges as a yellow tube surface, you can see that the tolerances extend into the smaller tool body:

based on that evidence, I created a temporary surface to use to split the tool body away from these tolerant edges:

and, I split the tool body using that surface.

The Combine works with the resultant tool body.

I realize that this is not a solution for you.  I only did this to illustrate where the problem is:  In the yellow body, along that edge.

So, if we want to understand what is wrong with that body, we would have to examine how it was built.  I know that you said that this is proprietary, so that leaves us at a bit of an impasse.  In the process of constructing this body, did you at any time do a Stitch operation with a high tolerance (maybe as high as 3 mm)?  If so, then that is likely the source of the problem, IMO.

I've attached my copy of the design, just FYI.

[marcocipriani01]

Thanks Jeff, I wasn't aware of the existance of such tolerant edges. I am indeed using the Stich command with a high tolerance, the issue is that I was expecting Fusion to create "real" edges when stiching, not tolerant edges.

To break the problem down, I isolated the initial surface I was working with (see attachments). The goal is to thicken it by 5mm towards the outside, and close the bottom, just like I did in the previous file.

The easiest way to do it would be to use the Thicken tool, but it doesn't work with this surface. It throws an error as soon as I select the rounded part in the rear of the model. To circumvent this issue, I had created several offset surfaces, patched the open parts, and stitched everything with a high tolerance.

I made several new attempts, and was finally able to thicken the surface by re-constructing the rear part using a loft. Can you please take a look at it? Why is this workaround necessary to make Thicken work?

Then, I tried closing the bottom of the "fixed" model by patching the bottom before the Thicken operation, but the Thicken tool refuses to work again in this case.

Finally, I tried by first using Patch and Loft to close and stitch that part. This yelds a new body I tried combining with the fist body to close the bottom. The Combine tool, however, throws an error I don't understand.

I guess there's something weird going on with the curvature of my surface, but I don't understand what exactly.

Thicken tool error:

Combine tool error: