Ikea items used:
Kallax 2×4 shelf 202.758.85, Oppeby tabletop 802.815.05, Kallax casters (x3) 002.886.57, Gerton adjustable leg (x2) 602.616.26, #10×3/4″ panhead sheetmetal screw from Home Depot (x18)
I first laid the tabletop on the cardboard on the floor facing down. I measured the Kallax shelf to see where I would want it to sit under the tabletop and traced it with pencil. I then put masking tape up to the line I drew out. In our case, I wanted the table top to extend further out on two sides than the other two, so that there is seating on one short end and one long side. The other two sides are in the kitchen area, so are more for prep space than seating.
After that, I laid the mounting plate for the Gerton leg on the two furthest out into the corners built in mounting holes. Since the Gerton does not thread into these holes, I just centered the mounting plate over the hole and traced out where all of the new mounting holes will be (5 per plate). I then drilled them out and mounted the plates with the #10×3/4″ screws I purchased at Home Depot.
I set the tabletop aside so that I could bring my already assembled Kallax shelf and put it upside down on the same cardboard (we have tile floors, so I needed a soft work surface). I placed the mounting plates for the casters one on each end and one in middle on the bottom of the shelving unit, put in the end tabs, drilled out the screw holes for each one and mounted them. The wheels popped easily into each one, paying attention to putting the locking one on the “kitchen” side of the shelf, rather than the “sitting” side.
I flipped the Kallax right side up, then mounted the Gerton legs to the table top and set them at one notch below the 90. Then we placed the tabletop onto the Kallax shelf. At this point, I rolled it into place where it will be and checked the placement of the top on the shelf. Once I was happy with it, I used the 90 degree mounting angle plates that had come with the Gerton legs to attach the top to the shelving. I did this by pre-drilling, then using more of the #10×3/4″ screws I had purchased (you could also use the original screws that came with the Gerton legs, but I had enough of these to use for this purpose also).
And that was it! I love it already!