I did a lot of research before I started building my 4 axis machine. I need to be able to turn 24" by 10' wood columns. Unfortunitly I did not discover
www.mechmate.com . Design is it is the best I have found and I am now rebuilding my gantry to their plans. Some of the highlights, free plans, active discussion group, laser cut parts avaliable from several different sources world wide, free CAD files avaliable if you want to cut your own pieces, source for V rollers at about 1/2 other sources( $186.00 USD for 12 V roller and 4 excentric bushings plus worldwide shipping),. When you go to this be prepared to spend abou 6 hours to read all the documentation and discussion on all phayese of construction. The addation of a 4th axis is fairly easy and is initial documentation is on my site,
www.turningaround.org,