Narrowest milled groove in 0.25" copper

[tartarus]

What is the narrowest milled slot that can be achieved in 1/4" copper plate? I am attempting to do something rather extreme and have a 7-segment display milled into a 3"x1.5"x0.25" copper plate, to later be backlit by appropriately controlled LED's. If I had my druthers, each segment would be a through-slot 0.17" in length and 0.035" in width completely through the 1/4" plate, but I suspect this may be problematic due to the minimum diameter end mills that are available.
Jim

[Tech2]

If you can design part of your device as a 2D sheet (all holes thru) we can do the slot you describe.

[tartarus]

Is the enclosed feasible? It takes a while to evaluate.

[Tech2]

To do this in one piece keep the slots at least 1/16" wide. Otherwise you can do narrower slots fully thru in a separate part that would be bolted to the base.