I'm diving into the idea of building afew cnc machines (a good friend of mine thats in fab wants one too) and there is so many ways of going about doing it. I just have some questions, pardon my ignorance.

I am sure most of you have seen that engadget article, and well..how accurate can you get with normal screw mechanisms like that? Now I don't mind gearing down the steppers to gain more persision, it also means that I dont need as powerful ones to get the job done-a win win as long as the controller mods can be made without being an ee. Any advice? Oh, and if I was to build a machine out of crap parts like that could it be able to cut acme screws or similar with the perscision necessary?

How much horsepower wound it take to cut various materials (aluminum, mild steel, tool steel)? I just have no clue.

Modding the life out of everything I get my hands on is a common trend. I am no stranger to fab and jury-rigged work. I want to build a small test machine to get experience on the engineering side of it. There's this crappy 1/2 horse drill press that I bought awhile back to use as a poor man's lathe turning down pvc for a custom exhaust valve. I plan on using the motor on that sucker just because I can...small xy table, easy vise mounting, though I am unsure of how to set up a z linkage. Off the top of my head I'm thinking counterweight and drill an axle hole for the stepper or some such. Any concerns advice on this one?

I'm just looking to build a passable (+-.002 would be nice) machine just as a test project at first, for wood or whatever the motor is up to doing. In the trifecta of good-fast-cheap, its fast that is the odd man out for me. I don't care how fast it cuts as long as it works without too much interruption needed.

Well thats all I have for starters, back to researching. I appreciate any help I can get.