Hi Peter, in this case this actually looks like a pretty clean font that will be good for filleting.

But the problem you ran into is that a radius of 5.0 is far too large in proportion to the curved areas of the font.

A fillet cannot often be calculated if you ask for a radius larger or nearly the same size as the curvature of bendy parts of the model, or also if it would cause small edges of the model to become completely enveloped and disappear.

In this case, you can go up to about radius 2, but not much more than that. Here is what it looks like with radius 2.0 :



Generally it is pretty easy to overestimate the radius of what will fit on a particular shape. So if the first radius that you try doesn't produce any result, try going smaller and smaller and see if that will get you anything. Sometimes you may need to go down as small as 0.1 or possibly even smaller to get a result. It depends on how tightly bent the curves are on your particular model.

- Michael