I have some file knives ranging from 3" to 14". I have had these for many years and they have maintained sharpness. However, this year I think they need some work. I know these are difficult to sharpen because I have done maintainence sharpenings but I want a like new edge and am thinking it may be a little more than I can do. Is there a commercial product out there that could work on these or should I seek a professional knife sharpening person?