Fillet Edges Overlapping Problem for a Ring


I’m a beginner at Rhino.
I’ve designed a shape that I made into a ring using the “Flow Along Surface” Command.
When trying to add fillets on the inside edges of the ring, they appear to be overlapping…

Can someone help me on this?
I’ve looked into the other posts but can’t find the same problem grr.

Many thanks for your time!

Flow Along Surface Mystery.3dm (3.4 MB)

Hi Margaux - yeah… that is because the flowed object does not meet its self cleanly where is wraps around - I’ll see if I can make it work - there are two problems, I think - one is, along the curvy edge, the ends are not tangent where they wrap around to meet each other. The other is on flowing there is no good way to accurately maintain that tangency even if it is there to start with - it is fixable in a geeky sort of way - hold on a bit and I’ll post a file.

OK, so it looks like we can skip the geeky bit and just make the edges tangent - see the attached file -
At step 1 the red and blue curves are not tangent to each other - that means that when the edge of the solid version of this same shape will not be tangent to itself when it wraps around.
At step 2 I’ve used match for tangency on the two curves, Blue to red. So Blue is now tangent to its other end, so to speak.

Then when the thing is extruded and flowed, it meets cleanly where it wraps around and the fillet can handle it. Note step 5- I’ve extracted the end caps of the wrapped shape and then deleted them - these are internal to the solid and not needed.

I used Flow, with the Line option and Stretch=Yes and not FlowAlongSrf btw

Flow Along Surface Mystery_PG.3dm (208.6 KB)


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Thank you so much Pascal, it’s brilliant !

When desiging the curve in the first place, I used a line as a marker and activated intersection to make sure both ends where aligned on this line. It’s not accurate enough then?

Your file is ultra clear can you just precise, for the newbie I am, how you managed to go from step 2 to step 3.

Many thanks :slight_smile:

Hi Margaux - the curve meets itself correctly for position but not for tangency - that is, the curve directions are a few degrees off from being exactly parallel - think of the slope of the curve at each end - one is slightly less steep than the other so there is a slight kink, or hard corner where they meet - do you see what I mean? I’ll make a file…


I see! Ultra clear.
When both lines have tangent ends, do you cut them both it in half to make a new line with matching ends?
That was the underlying question behind my last comment :slight_smile:

Ok tried the formula right now & I get it :slight_smile:
You can change only one of the edges position if you want!
Thank you for this cool tip !!

Hi Margaux - I am not sure I understand your question - but what I did was copy the the curve from one end of itself to the other, then Match for tangency, the original to the copy - that will move the second control point from the end of the original to line up with the second control point of the copy - The line from end point to second control point is what determines the tangent direction at the end of a curve - meaning you can also do this by hand by moving control points, but Match does it for you. At any rate the result is a curv with both ends having the same ‘slope’.

Tangent.3dm (42.0 KB)


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Question: why use Flow & not Flow Along Surface? Thanks for the precision

Hi Margaux - both will work - but in this case, I just wanted to point out that the mapping is really from a line to a circle and the surface part is not really needed…


ok I get it !
Trying to apply the Fillet Edge formula, something strange happens…
(sorry I’m the 1000 problems kinda of girl)
What have I been doing wrong again…

hmmm - I did not get that here, but I did everything on Windows/V6. Try this:

Start ExtractSrf and see if picking in the middle of that extra plane selects a surface - if so, see if rebuildEdges does anything… it looks like a surface edge gets messed up - post the file if you like.


Ok, I’ve checked and it’s because my ends are still not matching properly though I used the match & flow command you indicated.
The problem might come from the fact that the red line is not connected correctly to the blue line before using the Match command. I really cannot imagine another possible explained.
Do you have a technique that could put an end to this conundrum?
Many thanks again for your time

Flow Along Surface Mystery2.3dm (3.2 MB)

OK - I guess we need the more arcane stuff… I get that this seems like it should just work but there seems to be a combination of factors that’s a little tricky. There’s an underlying ‘thing’ that I mentioned originally but was hoping to avoid - when a solid like this is flowed, there really is not perfect control over how the ends wrap around and meet.


Here is what will work even though it is a bit weird and I’ll check with a developer about how to make the Flow stuff work better - it may not be possible to make seams as perfect as we’d like - you may simply be up against a limitation in the deformation stuff.

  1. DupEdge all four long edges of the flat extrusion.
  2. Flow these as you did the extrusion itself.
  3. Select the result and MakePeriodic (DeleteInput=Yes)
  4. Loft the four curves - make sure all the direction arrows match up. Use the StraightSections style in Loft, and ‘Closed Loft’ set

Flow Along Surface Mystery2_PG.3dm (221.2 KB)