Drill hits at edge of PCB

I am designing a PCB right now and due to the requirements for the size of the board and one of the components that will be mounted on it, I need to put mounting holes that almost touch the edge of the board. The thin sliver of material between the mounting hole and the edge of the board is probably going to be a problem so I would like to notch out that thin material with a drill hit - the mounting holes are 3mm and 4mm in diameter and I was thinking of using a drill hit about 1.5mm-2mm in diameter to make the notch. Is it going to be a problem to have a drill hit centered right on the edge of the board, extending past it?

This is usually known as castellation.
Costs a bit more.

I think castellation is when you have a plated half-hole - forming those is more complicated than just putting a plated thru-hole at the edge of the board and cutting through it with the mill. What I have are un-plated mounting holes and I just want to put a notch in it so there isn’t a super-thin piece of PCB that is likely to get broken off.