I can weld. I'd never build my own machine where I'm doing the welding. The fact is, the end goal is to create a high tolerance machine that works. I know if I'm doing the welding, it will never happen. Metal fabrication is a craft and I know I'm not a good enough welder, fitter, and fabricator. Remember, it's not only about welding when you build out of steel. You have to figure in how you're going to mount your drive and rail system. It's alot of drilling. A lot of figuring. A lot of fabricating.
A well made steel machine that is welded up is a superior machine to a bolted together machine out of aluminum. The thing I'm saying is, if you aren't talented enough to build the steel machine properly, your steel machine is going to be A LOT worse than an extrusion machine. Extrusion machines are A LOT easier to build right.
I'd suggest building something like this:
http://www.cnczone.com/forums/cnc_wo...erparts-7.html
It's very similar to how CNCRouterParts, ShopBot, and EZ Router build their machines. It's a good way to build a nice light industrial machine. It won't truly compare to a $50,000 machine, but it will compare to a $20,000 machine and that's pretty good.