Need help finding the best way to fillet these edges

Hi There

I have a project I’m working on right now that requires me to fillet the following edges of this polysurface. I have done a lot of filleting before on various projects and it is always problematic and requires many workarounds to get the desired result. In my experience it doesn’t seem that the fillet commands are the best or I don’t fully understand them. This is the most complex filleting I have needed to do so far.

What would be the best method to fillet these edges?

Here is the Rhino File:

Fillet Edges.3dm (1.9 MB)

Thanks in advance!

Hi Neil,

What radius fillet?

Preferably 0.5mm or 0.3mm.

First up, you have naked edges that need closing…

Oh I see… ill fix it

Fillet Edges.3dm (1.8 MB)

Ok pretty sure I fixed the naked edges.

Hi Neil,

Sorry to take so long to get back to you. Neither FilletSrf, nor FilletEdge are capable of filleting your object (nor is Plasticity, held up as a better filleting tool than Rhino). Rebuilding edges and surfaces to get rid of kinks that might be causing problems isn’t sufficient to make this work.

Your best bet is going to be trimming back the surfaces and sweeping curve to create the fillet. This isn’t going to be straightforward and you are going to have to create the trim lines in sections and edit them to meet cleanly. Here’s how I’d go about it (note: put lines, pipes, intersections etc. on different layers, using different colours so you can better see what is going on and hide different categories when not needed.)

  1. Create curves from the edges all around the top surface.
  2. Select the curves that constitute relatively straight runs and join them, then extend them at both ends by 1 to 2 mm. Ideally use the natural form of Extend, but some curves may turn too sharply, so use line for these - you’ll probably need to experiment to find which works best.
  3. Pipe the lines using a radius that matches how far back you want to trim the surfaces. 0.3mm say. If any of the pipes go haywire, undo, split that line segment from the rest, extend it and pipe it individually, then extend and pipe the rest of that line. Don’t expect the pipes to line up nicely, you’ll sort out the mismatches later.
  4. Create the intersections between the pipes and your objects. These are going to be your trim lines, but don’t trim yet.
  5. Now do the same thing for the remaining shorter, more curved edge lines. You are less likely to be able to join these and get reasonable pipes, so expect to do a lot of individual segments. Remember that they all need to be extended so you get a good overlap with the next piece.
  6. Hid the pipes so you can see the intersections. Where an intersection crosses an edge, use that edge to trim off the excess. Where an intersection is self-intersecting (usually creating a small triangle, dont worry about it. Where two adjacent intersections don’t meet precisely, adjust their control points so they do - eyeball the distances to the original edge to decide what to move and how much. You need to keep the curves smooth and the curves on the surfaces. To help with the latter, turn on control points and copy the isocurves that run through each point so you can use the as guides. In some cases, you will want to pare back both curves a little and connect them with a blend curve. You may have to create some segments manually. End up pulling the tidied intersections onto the tree surface to make sure the are lying flat.
  7. You should end up with two closed loops, one on the top surface and one on the sides. Select the two loops and use them to trim the intervening material. This is the time to get rim of any of those small selm intersecting triangles.
  8. Next you are going to create arks to sweep the fillets, but it is very take so I need to top there. I will resume tomorrow.


Thanks so much, appreciate all your effort in trying to figure this out.

I’m glad to hear that it wasn’t just me struggling to fillet this, Rhino seems to struggle with almost everything when filleting, this object’s complexity definitely doesn’t help matters.
Thanks so much for the detailed steps ill run through them and attempt it.

There are places in your model where you cannot fit a constant radius fillet. For example, in the following example, the red line is the original edge, the mauve surfaces are the trimmed back faces, the short blue lines are where planes perpendicular to the original edge intersect the faces and the mauve lines are blend arcs that represent the fillet outline. Notice how in this part of the edge, the mauve lines have to form S-curves instead of arcs in order to maintain tangency with the faces.

I guess, if we are starting from something impossible we should see any result at all as something incredible!