[jessewmc]

This can't be done in a single setup on a 3-axis, its not xy-monotonic (there are overhangs). Theoretically you could do it on a 3 axis by manually remounting the piece at different angles, but it would be hundreds if not thousands of setups. 4 axis is definitely the practical minimum to machine it.

[DannyBee]

It looked like the the overhangs can be machined with a small rabbeting bit (remember that we can use more than just end mills :P), and like i said, both my pieces of HSM software seemed to think it wasn't trouble (IE the simulated finished piece is within 0.001).

You are right that in practice, you would likely want a 4th axis rather than messing around, but a 4 axis setup is just not a big deal (the 4th axis on my woodworking CNC cost < 4k)

[alephnil]

You could not make it with a 3-axis CNC machine in one piece, but you could modify the design to make it possible without too much trouble. One way could be to make the base separately, and then insert the "blinds" that makes the digits separately.