Knowing greatest power is in a fine pitch thread, but of course they advance slowly, those conditions offer a lot of solutions to both. From manual standpoint, multi start threads generate little power but advance quicker than same apparent pitch (ie 8 TPI 2 start, looks like 16. Variety of press using multi-start threads to advantage are "fly presses", a pair of arms with heavy weight at the ends, threaded with the screw. The ram, about a half turn above project, is forcibly accelerated into the material. They're mainly used cold-forming but an operator, maybe with helper could do hot-work.
Concrete and rebar would probably work if there is sufficient tensile strength (cross section/ area of columns) but potentially 2x size of steel frame. Plate, C-channel and angle iron, more practical. BTW commercial screw presses went up to about 20 tons. That's calculable by thread pitch and applied torque.
6 to 7 tons wouldn't require welding. Enough Grade 5 or 8.8 threaded fasteners, properly placed in minimally sized clearance holes, using bolts, washers & nuts. It's how all kinds of 20 ton hydraulic presses are built, assembled often by purchaser.
I'd never bother with a casting. There are manufacturers of good quality un-plated allthread rods, you would prefer rolled over cut threads, definitely. The threaded barrel, is about the only thing needing some machinery to produce, bet a frame with three purchased nuts would be acceptable. A handwheel is normal, bet a salvage yard would turn up a cast tractor steering wheel. Might be one hanging on a barn, if one doesn't mind a little rock salt.......
A small wire winch for the table, some round barstock cross pins, symmetrical uprights right and left with the holes. There is more sawing and drilling than anything.
Of all features presses should have, I consider two (three) paramount; a] the head slides right and left in the top most frame and clamps into position. b] Uprights are open to allow long material. c] Bed is parallel in both planes, when owner builds tooling (furniture) that fits and slides in relation with top frame.
Few commercial units have those, most supply a couple notched flat plates to accommodate axles with bearings and that's it. Oooh big deal.
There should
(could) be punch holders, forming dies, Vee blocks at a minimum. 6 or 7 tons will punch 1/8" and 3/16, after-all.
https://www.americanmachinetools.com...punch_hole.htm
https://news.daytonrogers.com/how-to...e-free-formula
Writing this conjured a hybrid press, hydraulic with a screw ram. Not like the ordinary combination of a coarse ACME thread that just advances quicker than the air or hydraulic cylinder. Connecting them, that close-up hasn't focused yet. Don't know connecting is important, just secure alignment.
