Hi NightCabbage, the reason Chamfer did not work along that one edge is that it was not actually a single edge, it was 2 separate edges with a small empty gap between them.

For example if you zoom in to this area here:



You can see that there are 2 edges there:



For Chamfer or Fillet of an edge to work, it needs to be an edge that is a join between 2 surfaces, not one that is unattached to anything.

There are some other areas of that shape that have some significant gaps between the surfaces, like in this nearby area here:



Those pieces need to be built with greater accuracy so that the edges of the surfaces come closer to one another and can be joined together.

How did you create those surfaces initially? You should generally try to build things like that more directly off of the same shared curves so that they are closer to one another and can then be joined together rather than having larger gaps between things.

Does the update that SurlyBird posted above solve your problem though?

- Michael