Machine bed material

[JAZZCNC]

Pic of the structure that will be in the epoxy resins, threaded bar will also be added. The steel will be 1.7225 and with a surface roughness of .04um RA.

Pointless and not required machining to this level to achieve what you want.?

Pointless because having the plates machined before embedding into the epoxy will distort them due to thermal expansion and pressure, plus the extra machine time to achieve 0.04um Ra is wasted just for fastening rails onto.! You will be paying extra for this level of finish when it's not required.