Method machining for control flatness 0.03mm (milling)?

i have a material AL6061 by size 12.7 x127x600 mm to mill to size 12x120x600mm, but the momentous things need to control is the flatness 0.03mm. any method / process to achieve this critrial?
Answers:
If the machining can't do it, polishing will be indispensable.
.03mm = .0011", fairly tight for that large of a surface nouns. I assume you are referring to T.I.R. (total indicated readout) across the entire plate surface.This accuracy can be achieved using a planetary "lapping" process. Lapping will also say perpendicularity of both sides of the plate. There are shops that specialize in this type of finishing. Make sure that all machining, weld or any other heat treatment/material removal are complete before attempting to finish your flatness spec.

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