david weaver
You can do it with a large mill file, but I'd tape either the plane or the faces of the file (I'd do the file) so that it only cuts with the edge.

I say large because a large mill file will have larger teeth on it. There's no real rule to it, though, as long as you cut where you expect to cut and do a tidy job.

Chisels are fine if you know what you want to do with them and can do it.