It was actually invented at least a couple of hundred years ago for horse-shoeing work. Inventor was probably an ingenious blacksmith, and it was possibly never even patented
It is a tool used by engineers, mechanics and fitters for smoothing the surface of metal. Not as coarse as a rough file and more so than a smooth file.
It is a flat file (as opposed to round, oval, square, or triangular), with rather medium cross-cuts. It is used for filing common materials such as wood or metal.
A simple example is that a flat metal file can be used in metal working to file down (smooth) rough edges on a piece of metal.
The bastard file wasn't named for a person. This file is intermediate between fine and coarse, and at one time the term "bastard" was used to describe persons of "mixed race", so perhaps this suggested a file which was mixed. The etymology of the word "bastard" is obscure and the origin of the "bastard file" even more so.
A file is used for sharpening metal edges or tools
The harder the metal, the smoother file.
Gutenburg first invented printing that used separate metal letters.
No, a bastard child is one born outside of marriage. Generally obsolete language now, except when used in a derogatory sense. In this case it would mean a person of low moral standards - probably originating from the original sense of having no proper (married) parents. Alternately the term can be used as the identification of an awkward or unusual object. Often it is applied to tools that are not of standard size or configuration ( a bastard file: a file whose teeth configuration is in between a rough or coarse file and a 'second cut' file, a bastard sword: a sword which has no legitimate claim to being classified as either a single-handed or two-handed weapon). This could also be applied to a person.
A circular file is used to file the burrs of metal but is round all the way round instead of flat. A circular file is also slang for a trash can.
It is used for smoothing edges of a metal or wood
Many seem to think that the word "bastard" is a swear word. However, after quite some research, the word or term bastard is also known as being a child that was born out of wedlock. The word can also be used when referring to someone who is mean. The term is very unpleasant to use towards people.
If a hole has been drilled in a metal sheet, the round file is used in the created hole to remove rough edges.