when I built my guitar a couple years ago the area where the nut rests ended up being at a slight angle, call it 10 degrees, from square, now I'm replacing the nut and I am honestly not skilled at matching this angle* (I had help from a guy I paid at the time that certainly helped this process). I am thinking if i can make the small area right behind the nut 90 degrees with the end of the fingerboard this process would be a lot easier, the only thing I have come up with is using a file as wide as the nut and slowly cutting a groove back there and put some painter's tape over the top edge of the fingerboard so I don't inadvertently shorten the scale of the guitar.
does this sound like a sold plan or can you guys give me any idea how to do this and not screw up my guitar. If I have to spend a little bit on a tool that's ok too (like less than $20) I no longer have access to a table saw or router, but those sound frightening to work so close to this finished area anyway.
thanks
* not skilled meaning I am on my 3rd nut trying to get this right, telling me to take it slow and check often isn't enough for me apparently I just can't judge this right.