I have sharpened files with vinegar for years. Any file, cheap or expensive, can be made to cut wood effectively and cleanly if soaked in vinegar. I got curious when I saw a label on some edged tool that said "chemically sharpened". Found out that acid will eat the metal all over at the same rate, pointing up a rounded tooth edge as the opposing slopes get eaten away.
I thoroughly degrease, then soak for a few days, neutralize with baking soda, rinse in very hot water, and dry. Duration of the soak will depend on the original condition of the file. I will say that the first few I did were soaked too long and the edges were weakened. Those files became no good to use on metal.
When done right, the file will actually snag your fingerprints when you lightly rub your hand over it. It makes a world of difference using these on wood. "Cuts like butter".
My favorite large shaping file is a hoof rasp called "The Plater's Special". Medium-fine rasp on one side and file on the other. Evidently, racing horses get thin shoes (plates) on their feet, and farriers need a very good rasp to get the job done.
Good luck and remember,
THR rocks.
