Sounds like a video card problem.

Try this. After blending, change the resolution. I have sometimes had the model reappear this way as long as when you highlight something the entire profile of the part is there.

Confirmed. Not sure what is going on with your model. I'm guessing the hollowed out part of the inside of the ring causes this disappearance.

I've done rings in the past but I have taken a surface approach to make the surfaces and then make it into a solid. I have better control of the profile when using curve profiles.

Is the hollow required around the ring hole?

It's because your ring is hollow and the edge that you want to blend doesn't make a good join with the outer shell. I suggest that you need a different approach, and should make the shell solid up to the line in the image, before you insert a tube for the finger hole.

I put a cut section through the ring and extruded a solid from the profile of the cavity. There're lots of ways, though. Draw a rough profile that encloses the cavity and extrude, or cover-surface it and thicken. I think it'd be elegant to make the finger-tube outer profile elliptical, or with wings on the circular profile, so it'll block off the cavity automatically.

I would say it is not an ACIS filleter limitation. It has to do with a badly trimmed surface inside the ring cutout. It appears to me to be a result of having the model "shelled", then running the cutout of the ring, which did an intersection of the inner and outer shell, right at the seam point of the cutout circle.

So here is a picture where I deleted the outer surface.

[ATTACH]4301[/ATTACH]

You'll see a fragment edge protrude from the tip of the top surface to the lower one (This should have been a clean cut). It emulates from the inner cutout circles seam edge.

The filleter is having an issue with "traveling down and around this entire area" with it's auto chain mechanism. If you select the opposing edge from the one you specify in the original screenshot, then it will also fillet, like a face fillet, because the chain selection will bypass this malformed edge and the filleter can consume the entire area.

These types of modeling defects can be avoided by paying attention to keep "seam edges" out of critical areas of booleans and trims and such.

FYI

Ok, so I finally figured out how to unstitch the model properly with ViaCad, using "change object type" convert to surfaces (One of Tims videos) then I could hide that outer surface and ViaCad would show the intersecting surfaces in that area well...

The fix would be that the fingerhole size needs to shrink, the shell needs to be smaller value, or the outer size of the ring needs to be larger, to allow for volume in that area.

Thank you all,

befor i finish the ring, take a look how the casted ring looks in silver.
nice blending ;)

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Hallo Jean-Francois ,

in this case i play around with shapeways. They print it in wax and cast it in silver.
I had to to clean a little the surfaces.
Normally i send it to a wax 3D printerservice and after to a casting company.
they can do it in also in gold and platin.

so,
now the ring is finish.
Thank you to all of you, for helping me to make this model with ViaCad.
The ring is filled with concrete.
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Danke, merci, Thank you ;-)