How to fillet the corner of a surface

Hello, I am trying to fillet the corner of this surface but cannot figure out what command should use. Any idea? Thank you.Test.3dm (88.8 KB)

Hello - in this case, ‘Fillet’ the edge curves, then Trim the surface with the resulting curves. Since the edges are not planar, the Fillet command will not work. You can use BlendCrv and and adjust the curves by eye. To get a consistent setback to the the blends, make a sphere centered on the edge end points.
A trick is to ExtrudeSrf the surface as a solid and then FilletEdge the vertical edges, then ExtractSrf the surface you want and delete the rest.

FilletTest_PG.3dm (41.7 KB)

I have an old vb script that fillets non-planar curves, I’ll try to dig it up or write it in Python.

@hungwai.lim, @norbert_geelen - in case it helps, this thing does, or tries to do, curve fillets for curves not in plane - if you give it edge curves, currently it will only make the fillet curve, but free curves as inputs should obey the trim and join options.

Note you can use it to make a ‘fillet’ between two lines that cross without intersecting:

or for making non-rational fillets in the regular planar case as well.

See if it does anything you like.

To use the Python script use RunPythonScript, or a macro:

_-RunPythonScript "Full path to py file inside double-quotes" (10.8 KB)


1 Like

You can’t fillet single surfaces. You could thicken it then solid fillet the corners.

1 Like

I tried BlendCrv but cannot find an easy way to do it precisely, the sphere is a good trick. Thicken the surface is also works. Thanks a lot!

Wich is a shame, really.
I know a cornerfillet and cornerblend command for surfaces would make my life easier for sure.


You can’t fillet single surfaces

@norbert_geelen, @Stratosfear, @hungwai.lim - here’s a first try at that - see how this one works for what you need: (9.0 KB)

To use the Python script use RunPythonScript, or a macro:

_-RunPythonScript "Full path to py file inside double-quotes"

The fillet will only appear arc-like from a particular view or plane - I added options to use the World or CPlanes as the basis for the arc shape but this might make a mess pretty easily if the chosen plane is too skewed from the ‘natural’ fillet plane. The Auto option attempts to find this natural plane and should probably be used most often. I’m not sure how useful the other plane options are, I was thinking that one might, for example, want the fillet arc to appear ‘true’ viewed from the top and not from the surface tangent plane there, so that is what the plane option allows…


Making an exact raduis corner cut of a surface could be done this way, too:

  1. Use the “Fin” command (Extrude curve normal to surface) to extrude the two adjacent edges around the corner.
  2. Then use “VariableFilletSrf” (Variable radius surface fillet) to create the desired radius fillet.
  3. Untrim the latter with the “Untrim” command (sometimes that step is not necessary).
  4. Use the fillet surface to trim the surface edge.

I think it’s the better way and simply…