This one came from reading an old Popular Mechanics article. That's why I recommend you keeping an eye on those guys...
During WW 1, or is it WW2, large machines were built, that required large castings, and so they resorted to cement or concrete instead, to minimize the need for metal and the extra work.
A man called V R Romig, then, took the quantum leap of using that, not for HUGE machinery involved, but for TINY garage machine-tools, i.e. for us Gizmonian Geeks!
And, with all the new materials available since, you can make the composite machinery out of anything conceivable, and avoid casting as much as possible! I'm thinking Fiberglass, or even Silicon, and all those new ones that came later!
In the next chapters, you'll see some other ways to make composite frames and machines; But as much as lathes and other machine tools are concerned, just take the old plans, keep using the metal pieces, but replace the castings with cement, bolts and wire frame, use plain old wood molds to pour the cement mixture, you're in business!
Remember, that way... There's practically NO SIZE LIMITS!
Here's some neat news from Ponoko:
The lathe above is by Pat Delany, who has made the plans available for free. The approximate cost to make it is $150, which is truly remarkable for a metal lathe. The idea is based on the work of Lucien Ingraham Yeomans, who pioneered the use of concrete to make cheap machine tools during WWI.