Hi AJ,

> What I do is I open the hinge_cusp.3dm file, select the object, select the
> fillet command, enter the radius (0.3) and nothing happens.

It looks like those steps work ok in the current v3 beta, but not in the v2 version which is the version for the trial.

I've attached here an updated version of the model which should work for you in v2 as well as v3. For this version I deleted the "side walls" that were made up of 3 coplanar pieces and then used Construct > Planar to build just one big trimmed plane in those spots instead of 3 coplanar fragments.

Sometimes the filleter also doesn't like to have multiple coplanar fragments next to one another instead of one big single planar surface, but in this case it's been fixed up in the more recent v3 versions to work.

- Michael