Back in the 80 s I worked for a John Deere dealer..the owner was into going to government auctions..he came up with these pipe frames the perfect size for welding table frames....had flats on them to mount castors...including bent pipe ..2 inch...he sold them to local farmers....I found one in his scrap heap..when digging it out I discovered it had a 3 inch thick cast steel top ..he gave it to me ...I cleaned it up and what I found is a machined surface perfectly flat...
These made the ultimate welding table...I drilled and tapped and bolted a 3 inch angle around the edges...bolted on 2 vices and fabled a folding cutting table on one side out of a piece of bar grating...mounted it all on industrial casters also found in the same junk pile...this stuff was ww2 surplus and built like a tank...the cast top is not only flat but weld splatter won't stick to it...
