Can't help too much not having built a machine yet myself, but I will say one thing. Avoid unsupported rails like the plague. You'll want either supported rails with pillow blocks, or some rails/trucks or similar.
Ballscrews tend to be the "best", but as you mentioned, are quite expensive.
One thing you have to decide is which is more important, accuracy or speed. Accuracy will lower your speed, while a higher speed will lower your accuracy (generally speaking). This makes choosing your lead screw, etc. a pretty vital decision.
Hope I helped a bit,
- Jesse |