Is there a generic procedure for a certain fillet

Let’s see if I can explain this without a picture…I want (well I don’t want to but it’s the spec) to put a fillet on an edge that fades away some arbitrary distance along it. The radius doesn’t actually vary to 0, it just kind of rolls off the object, i.e. it was filleted to some different surface and trimmed off. I did one on this model already that was easy, but it was an INSIDE fillet. I think I see one or two ways I could do this one, but I’m just wondering if there is in fact some sort of known generic procedure to follow?

Hi Jim - does the thing stay tangent all the way?

Or like so, maybe?


Just to get it right? Something like this?

Hi guys,

No it’s a different thing, it only stays tangent on one side, the other side veers off the part and is trimmed off.

Hi Jim - like this:

I extended the regular fillet edge curve with an arc to a point on the object’s edge and Sweep1 the trimmed end of the fillet on that. Of course it’s a box so no tangency problems - on an arbitrary surface I’d trim with the extended arc first and then sweep on the edge with Follow Surface set in Sweep1.

I’m still not sure this is it but…
CutOffFillet.3dm (161.7 KB)


well, I don’t know. There is one trick I do when going from sharp to smooth edges. You can create a radius with an diameter of your tolerance and from there you blend. Afterwards you can delete the tiny fillet. Hope this at least helps.

Do you mean what in product design is known as a “cut off radius”?

I guess you might call it that, a quick search doesn’t confirm it for me. I’m getting a result, the process just seems a bit freeform.

I recovered my deleted post…

Ok, thanks, a picture says more than words ; )

That’s not a cut off radius indeed. 3D software cannot know from where (often the start) onwards the surface shall leave tangentiality or curvature, so in high-quality consumer products or automotive, you would do this manually, also to avoid a three-sided surface. I’d do it just like you did it, manipulating the CPs on the two green “free” sides to gradually transition from G1 to 90° where you want.

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Why not post the 3 surfaces that surround the fillet…

If the angle between the 2 surfaces at the end point of the fillet is 90°, then the command testfilletsrfcrv might be one way in Rhino to produce a correct rolling ball fillet solution. You need to create a curve on the one surface and then run the test command.