You might have noticed, in the previous picture a ring of bolts around the upper neck of the steel tube. This was done to allow for a circumferential grip around one of the disc brakes that was to serve as a perch and adjustment plate on which to mount the disc brake chosen as the seating for the AVX. The photos will I hope make this arrangement clearer.
The ‘perch’ disc was slightly loose inside the cylinder and so a ‘sleeve’ was made from some scrap galvanized sheet and tack welded to the inner surface of the cylinder at its mouth. 8 equidistant 6 mm bolts were then fitted around about 2 cm from the edge and the 3 mm cylinder wall tapped to receive them. They were temporarily held in place by nuts on the inside acting like lock-nuts against the thread in the cylinder wall.
These nuts were later removed and threaded on the bolt on the outside of the cylinder behind the head so that when the bolt was threaded through the cylinder and screwed down to the required depth to catch on the wall of the brake disc the nuts would then be tightened against the cylinder to secure the bolt’s position. So basically the “perch” disc was held by these bolts acting as adjustable grub screws that allowed coarse alignment of the whole pedestal surface to point the AVX in the North/South direction. The AVX’s proper axis alignment screws would then be used for final fine tuning.
The AVX seating brake disc was next placed like a top hat above the perch and three equidistant 13 mm holes were drilled in the rims of both discs to allow the insertion of three adjustment bolts that would serve to make the final fine tuning of the AVX seating surface in the horizontal plane. This setting would be done with the pedestal in its final place anchored to the concrete pillar at the center of the observatory.