Ironically having to settle for that, even, due to the cost of steal. My new welder’s still in its unopened packaging.
I see you opted for 2x and 4x. Big spender. 
My top board is 3/4" plywood 48" x 48" on a 44’ x 44" Kreg base. I did notice a little flex in the middle so I’m adding another 3/4" plywood on top of that. I will likely also add a couple of 2 x4’s trimmed flat first and mounted underneath. The X-50 feet mount directly over top where the legs of the Kreg base are.
A number of options
My current set up for my Wood Worker is a torsion box
18mm Moisture Resistant MDF for top, bottom and torsion grid
18mm sheet on base grid made up using 100mm wide strips
Top and Base screwed to grid using counter sunk screws and glue
Grid constructed using glue and pocket hole screws
Torsion box mounted on a frame made from 4x2 regulised timber
Whole assembly levelled in workshop a lot of time spent with shims under the base of the frame
Its important to make each stage as accurate as possiable
Torsion box to be parrell true and square, frame to be the same any discrepancies will be in the workshop floor and needs to be made up as rigid as possible, once shimmed level leave over night or even for a couple of days if you can for any settlement then recheck level, reshim if required and secure to floor using brackets and fixings
I then mounted T track and 18mm mdf as my waste board secure The Onefininty to the torsion box checking for squareness and levels, surface the spoil board and adjust tramming as required (lots of machine set up and adjustment threads on here
My machine is used daily making a variety of items, jigs for use in the workshop as well as items that we sell.
There are lots of threads on here regarding board flatness, router/ spindle tramming accuracy chasing thousands if an inch, i agree the set up needs to be accurate but just take a step back and look at the set up, I appreciate that these points may apply to some but not all owners / users
Most people are machining wood, wood will move more than a thou in the blink of an eye
Most Onefinity’s are mounted on a wooden base of some kind again moisture / temperature will cause the base / torsion box to move
The Onefinity appears to be the best designed and most rigid set up in its market area however I am sure knocking or pulling on any of the rails will produce errors of more than a thou.
A long time ago I served a 4 year engineering apprenticeship (early 80’s) and we worked very often to a thou and at times a tenth of a thou using lathes, mills borers and grinders on items as small as 1/8th stepped dowel shoulder pin to bores on cast iron housings that had to to within a thou by turning and large casting weight 3/4 of ton that had to be true and square to within a couple of thou over 3 or 4 ft in order to achieve the required tolerances machines weighing many many tons were used bolted to large concert foundations some of the machines having casting voids filled with concrete or lead with regular maintenance to slide ways and backlash adjustment. Cuts were taken and sometimes retaken castings or steels were rested sometimes being roughed out taken off the machine and days or weeks later put back onto the same or different machines to be finished.
The parts and castings were for high speed manufacturing equipment in the food canning industry where they produced thousand of cans or lids an hour and would run for weeks at a time so the tolerances were important and yes even with all that care with heavy duty machine tools a workforce with a large number of years experience items did fail inspection and had to be scraped or reworked
Sorry for the long ramble but what I am trying to say is don’t get hung up on accuracy from what is a really well made hobby / light industrial machine
Take your time enjoy the Onefinity keep every thing flat and clean and achieve what you need to not what you want to.
A final note we all aim for flat spoil boards, well trammed spindles etc. A lot of the time we place a piece of painters tape on the spoil board with a dash of super glue we then place a layer of painters tape on the material with a squirt of activator and press together, what’s the accurate repeatability of that process? Even back in the 80’s we used to use a torque wrench on the bolts to secure work down and also a torque wrench to tighten a vice up on a machine and still we didn’t always get it bang on
Please this post isn’t a dig at anyone and apologies to the OP for a long ramble only vaguely linked to his original post but I have seen too many people disappear down rabbit holes chasing things that they really don’t need to
I am no expert but if anyone want’s to contact me for any help or thoughts on set up they drop me a line, this is a great forum and everyone has their own thoughts and opinions
D
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Man, SurfinGump. I’ve really got to try to catch up on your table. I really like the idea of putting the vertical opening in the center like that. Having got to the point of being a day or two away from finishing my cabinet, it’s too late to incorporate that in my design. I went with a 28" wide by 18" deep removable panel in the front of my 7" thick torsion box. Sitting on top of a 40" tall cabinet gives me the ability to cut joints in the ends of boards more than 48" long and 24" wide, in theory at least. We’ll see how it works out once I get the CNC installed.