The Book "The Recycling,Use & Repair of Tools by Alexander G. Weygers isbn 0-442-29357-7(cloth) or 0-442-29358-5 (paper) chapter 19, Files,Rasps, and grindstones pg 71
How to clean dirty but sharp files,acid sharpening....Making Files and Rasps 73...a File cutting jig. etc.
I think you can now get all three of his books in one on E-bay...it a good read and as pointed out you need to make one sometime