i have sharpened large 8, 10, 12 inch files. you clean them, paint them with a cold browning solution. put them in a high humidity place,coat them everyday,and when they look like you have ruined them,take them out and put them in a full strength muratic acid solution for about a hour. works on smaller files, 6" and 8" , but to a lesser degree,these will pin the shavings. works on mill or bastard files. I do a lot of work on old wrought barrel and refiling the flats gives a file lots of grief. if you take the smaller files and rub them with fine and across the teeth, it helps to prevent the plugging.