How to drill 4 mm holes in 1 mm. Steel and avoid grates?

Maybe try something on a scrap and see if your skills and available tools are going to give you the results you’re after.
If all you have is a drill, maybe make a drill guide from some wood or plastic, and then clamp that to your metal. Use cutting oil and go slow.

If not, then do what was suggested in post 21…
 
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There are two solutions:
  • Cut out the entire area, and cover it with a pre-drilled piece of steel (or aluminium) sheet from inside or outside.
  • Take a piece of aluminium sheet, draw a matrix on it, tighten it to the steel sheet at many points, the closer to the holes to be drilled the better, and drill through.
I bought very nice perforated sheets at this firm:
https://jurotissu.hu/
Fortunately I found smaller pieces but large enough for me in their debris box.