The first step was to build the box frame to hold the two tubes. Jim Mettler took charge of this part. The frame was made from 3/4" square aluminum tube (1/8" wall thickness) held together with machined fittings press-fit into the ends. The fittings were made very slightly oversized, with the corners of the square pegs rounded to avoid splitting the square tubes.
After a few hours of cutting aluminum tube lengths and pressing the fittings into them, the basic frame took shape. Then we added two 1/8" aluminum sheet plates to hold the altitude bearing, and since one section of the frame has to be left out so that the frame can be moved in altitude when on the pier, more 1/8'' aluminum sheet was used as a gusset in the back to keep the two sides from sagging towards each other.
(Left) Jim Mettler uses his press to attach a fitting to a tube section.
(Above) A close-up of a corner fitting about to be pressed into a tube section.
After the frame was complete, the mount bearing was created.