cutting a groove with a drill? Is it not lot bigger to handle for this kind of job? would not a small triangular or flat file with manual filing do?
The problem is that you should not cut the groove through the entire length. Doing this with round file looked a bit difficult.
The drill in the picture is a small 12V drill used for PCB drilling. It is smaller than Dremel 300. But having the Bit of the right size (or a Sanding Mandrel ), you can even use the bigger drill running at lower RPM.
But if one is proficient in doing this using File, it should be fine. It was my first attempt and using the drill came as most convenient to me.