How to drill a hole on diecast toy using dremel?
For delicate work in soft materials, I still like to use my old wheel brace (hand drill).  I've used it on plastics, wood and aluminium when I don't want to risk marring the surface as I break through.  Securing the workpiece is an absolute requirement as it's a two-handed tool.  I'd start with a 2&nbsp;mm drill bit, then use a 4&ndash;4.5&nbsp;mm bit so you've got the minimum at the next step.

You could then square off the corners with a needle file.  My square needle file is about 2&ndash;3&nbsp;mm at the widest point. This will give you much squarer corners than any rotary tool can provide.  Even if you start with the dremel, you may need to finish off with a needle file.