Each stair tread required a little more than a sheet of 3/4 furniture-grade plywood, which is cut on a CNC machine. A single stair tread takes about two hours to assemble, so the completed stairway took about three full days.
The step by step on how to build a DIY spiral staircase
A three-inch schedule 40 steel pipe was welded to a steel plate and bolted to LVLs in the floor frame.
Ben glued the plywood to the steel pipe with construction adhesive and the plywood to the plywood with wood glue. He screwed it all together with three-inch finish screws
He also drove five-inch screws up through the layers, where two treads meet, so strengthen this potential weak spot.
To finish, he sanded the heck out of it and applied Minwax Polycrylic.