making very fine slots...

[John S]

Oops missed that bit.
What about doing this on a 54mm disk and pressing a 3mm ring on afterwards ?

[BillTodd]

laser - I doubt they will cut copper alloys
edm - yes but at a cost
0.2mm milling cutter in a top-notch cnc - no problem
0.2mm milling cutter in a converted drill/mill 1 or two notches then snap...

How about photo-etching?

[John S]

Laser will cut brass but the edge finish is $hit and at 0.23mm wide probably impossible.
Spark eroder will do this no problem but you need a graphite or copper master and cutting this gives the same problems as cutting the slots.

What is it for ? can the design be altered to suit a better method?