Let me make some comments on 80/20 stuff. First I think it's great stuff, handy and versatile. Reasonable in price, since you can get most of what you'd need from the EBay store, at reduced prices. With that said, I'll move on. The question keeps coming up about the bearings, "are they accurate enough", what about "drag". Well, I think properly applied, and adjusted they are fine for all but optical type work. Also ,I think it has been rendered moot, by Ahrens bearing carriages. So, I think that if you want to use the extrusions as material for your next build, go ahead and do so, you will not be sorry. But, do not expect it act like 900 lbs of cast semi steel and precision hand scraped ways. In other words, it will not be a vertical milling center from the early 1930's. You won't be able to hogg out, 5/8th". of an inch at a time with it!!. I just thought I'd add my take on some of the lingering angst over 80/20 stuff. Thank You.. Oh I plan on building my next machine with 80/20 stuff entirely,3 ft x 5 foot platform,

I built a small mill and lathe with it. They work so much better than the X2 and minilathe that they replaced. Both very accurate and strong.
They won't hog out 5/8" material, but can easily take .025" in mild steel and .05" in aluminum without any trouble.
I didn't even fill these extrusions like I had originally planned.
80/20 is fine material for a benchtop machine.