you can buy prehoned tubing ID for the outer tubes and get the inner tubes ground. If you don't grind the inner tubes you will probably have some binding.
tubes typicaly aren't made perfectly round and they are usually bowed quite abit. You can get outer tube preground to but it is less common and I doubt you will find a matching outer. (but wouldnt that be cool)
If your using bushings in the outer tube you don't even have to worry about the inside diameter finish. so any straight tube will work.
looks like a good design although abit complicated on the ballnut area. Should work great.
That video at source forge was awsome! There is less metal in that than My mill and its bigger and looks to be more ridgid. I will definitely have to make one of these for myself! Hopefully the software is up to snuff for the 5 axis stuff.
thanks
Michael T.
"If you don't stand for something, chances are, you'll fall for anything!"