I am sure the small companies who did this work amongst other things they did like re grinding milling cutters. Where left over from WW2 because over here until the late sixties the words "Make do and mend" did mean something also tools where still very expensive. Being a rather inquisitive young individual I did ask what they did with the files, this was what I was told. The worn files where heated to bright red destroying the temper then rolled between two pattern mill rollers applying the new file pattern on the file, the original manufactures name on the file was obliterated in the process. Then the file was re hardened for use.
