Had a Jeep once with a cast iron head. It got hot and cracked.
Seems like a lot of crawler tractors have weldments. Cranes, etc.
Used to work for CB&I making (nuke and non-nuke) vessels, storage tanks, etc. CB&I wasn't in Chicago, didn't make bridges and never used iron. Never got to work on one of their water towers. :no: While we would occasionally preheat weldments, there was never any annealing, a.k.a., stress relieving on the jobs I was on. From my materials class as an undergrad MtlEngr at AU, stress relieving seemed to be all about understanding the material's phase diagrams.
I believe both Robust and Oneway have been making their lathes for awhile. I've never read/heard any complaints about cracked welds when I was doing research before buying one. Might be a good question for the English family however. Everytime I've called Robust, I've talked to Deb. She'll know. If not, Brent will. Check his bio. He seems to have the technical background to make his machines work.
I know nothing about OneWays.