Thanks to everyone for responses to advice re. cutting 1.6mm slot. Very useful info. I am not experienced in buying such tools (e.g.saw with 1.6mm blade). Any suggestions for a specific model - would a Dremel do it? I have seen ads for fine circular saw blades with 1.6mm blade, but they don't say how they are connected to a tool. I have never used those sort of tools. Jacob's comment about a straight back to the slot is very useful. It does not really matter if it is straight or diagonal.
Thanks everyone.