Asking because a lot of people new to CNC (as you question seems to indicate) build their machine and don't know they have to spend a fair amount of time fine tuning to get the accuracy to where they want it to be.

Not sure if that's the case for you, but pointing it out, just in case. :)

With the 'metals' thought, be careful there. Soft metals (eg most aluminiums) are a lot easier to mill than the harder ones (eg cold rolled steel). It might be better to stick to soft metals for a while unless you're sure. :)