Ok you lost me
you said your engraver could do a 3mm depth, with a 3mm cutter @ 250mm/m
depends on how big the spindle motor is. the nc machine in this thread would never do it, infact it tells you the aluminium parameters...
1mm/s = 60mm/m
0.002" cut depth = 0.005mm/pass
Assuming we want to go 3mm deep thats 600 passes, with lets say a 200mm tool path (rater optimistic imo)
((200/60) * 600)/60 = 33hrs
I may be guilty of not reading the original thread, although my gestimates arent too bad, the feed i guessed just about right, but i got double the z feed over twice the distance. The toolpath length is shorter in this guesstimate but its almost certainly too short. Depends on the block design.
]JR[