The way I read that image, all the more or less vertical surfaces are clipped by the top plane with maybe a very very tiny fillet there if at all.
-Pascal
Hi
Why does it need to be filleted if itâs going to be printed and itâs hidden from view? I would focus on making it more robust in the area where the original part failed.
Pascal,
Not until I had taken that photo and was able to see the part so much magnified, did I realize that flat spot on top of the part. That section is not filetted at all.
Maybe the designer of the original part had similar issues and decided to just leave it flat. I will now try to model it that way.
Stratosfear,
As I explained above, I am fairly new at using Rhino. I wanted to challenge myself and use fillets in this part, precisely for the reason that it was difficult, not because they are needed. And before I had taken that photo of the part I had not realized that there were no fillets on either side of the part on top.
I realize that the replacement part does not need to look like this at all to be functional. However I wanted to duplicate the part more or less as a learning challenge, and when the fillet issue with the naked edges showed up I knew I was stumped, and did not know how to solve it. Even more so since I had been successful in modeling the other part of the lamp clamp set without any fillet issues. That is why I posted the original question.
The fact that this part is hidden from view does not influence my design decisions. I am a jewelry designer, having worked over 40 years in my field. In jewelry parts are very often hidden from view, and customarily those sections are given just as much attention to detail as the sections that are visible. That is and has always been how I approach my work. I was trained that way in Germany. I think overall design is very important whether parts are visible or not. When you hand a jewelry designer a piece of jewelry, the first thing heâll do is turn it over and look at the back.
However, that may be a different discussion not necessarily suitable for this thread.
if you look at the same section except the side closer to us in the picture, the flat top isnât thereâŚ
i imagine the designer of the original part didnât draw it with top like that and itâs just the result of a not-so-accurate molding process⌠like- âwell, weâll make the mold like your drawing but who knows how exactly the plastic is going to turn out once we dump it in there⌠if thereâs any excess, weâll just sand it off⌠the only thing important here is that to top & bottom surfaces are parallelâ âŚetcetc.
in other words, i donât really think you should try to copy what youâre seeing in the picture⌠itâs a manufacturing defect as opposed to a design choice.
the side nearest us in the picture doesnât look like it was sanded down and really, it looks a lot like strosfearâs first example in this thread⌠except with tighter radiuses (yes- âradiusesâ passes my spellcheck 
)
i guess more of my point is:
i get it that youâre wanting to duplicate the original part as a personal challenge and thatâs fine⌠but-> this part isnât pristine or perfect or a good example of something to try to copy⌠in this circumstance, it might be better to realize the designerâs original intent then realize what happens when itâs run through a not-so-perfect manufacturing process⌠then, to stay within the bounds of your personal challenge, try to design as the designer meant it to be and manufacture it with more precision.
(or something like that )
Filets are sometimes great challenge.
Keep trying 
Ăh, why shouldnât it be suitable? Where and how one uses fillets isnât only a question of aesthetics, but also one of how the forces are spread through the material. And, though I am no jewellry designer, I always look at any piece of work from all angles possible.