We wanted the top Y rails to be able to be shimmed if they turned out to be tilted up/down over the length of the table, (also we needed to part the gantry up into smaller heavy pieces so that we could still manage to lift them all into place without heavy machinery assistance) so will be bolting the upper gantry to the gantry upright legs using ¾” steel plate and 4 bolts per side. The plate pads can be seen bolted to the side of the upper gantry pre assembly.
When we initially assembled the whole Gantry we used large pieces of angle iron to get the pieces straight and help secure it all together, didn’t want any pieces falling on our toes; that would be the end of a work day!
The next part would be to figure out what would be adequate bracing for this huge top heavy gantry, remember there is still a z-assemble to be out on here which will be 300+ lbs.