MY take on well known Bender

[ncollar]

Garage nut
One thing you might want to do is make a "D" reamer. They are easy to make and will open a hole just a few thousands
creating a nice round hole. Google "D" reamer.
Good Luck.
Nelson

Here is a pdf file on reamers for some ideas. http://billhaneman.ie/Reamers.pdf