I realize that fillet is a rather capricious command, but why can't I make a fillet of a straight segment and a curve?
And a straight line and a straight line form a fillet perfectly.

Video in GD: https://drive.google.com/file/d/1C7a1JcG62CTmd6q2b-JVkcXVMaEyPrl0/view?usp=sharing

Hi Moi3dFan,

I had the same question a while ago, but after playing around with it I realized that this is a fact of geometry rather than a software limitation. It's not possible in general to draw a circular arc tangent to any 2 curves that aren't in a plane. You can try this out with "Draw curve" > Arc > Tan and you'll find that in many cases there's just no way to do it.

The curve that you're ending up with there at the end is not a circular arc.

But, to do this kind of thing you can trim the curves away from the corner a bit, select them both, and then do Construct > Blend.

- Peer

Hi Moi3dFan, just to reiterate what Peer writes above,

re:
> but why can't I make a fillet of a straight segment and a curve?

It's because those segments are not on a single shared plane.


> And a straight line and a straight line form a fillet perfectly.

The 2 straight lines are coplanar so that's why that one works.

Basically, the job of curve fillet is to generate an exact circular arc, which is a planar curve. So it's generally required that all 3 pieces - both input curves and the arc - need to all be on one common plane.

The result you show from solids filleting is not an exact circular arc because it comes from a diagonal cut of the fillet surface.

- Michael