I make plenty of file knives. What is the brand on the file? That is a critical factor in how well the steel work up into a useful blade. Nicholson, Black Diamond, Save Edge...usually good steel to work with. Especially if it's older, say 40+ years old or so.
Post the brand name if you can...pm me if you'd like to discuss a knife.
Here's a few I've done in the past: