A Key need in the making of what will be ceiling-mounted work is some sort of overhead work holder. This holder must simulate the attachment method of the final installation, yet allow delicate work to be performed at convenient heights and angles.
The holder built is a sort of manual jib crane, and appropriate for fairly small (~1 cubic meter max), and light (~100kg max) work. It allows quick position adjustments in X,Y,Z, and rotation, and is fairly rigid when adjustment axes are tightened down.
The main horizontal structure (a cantilever) gets thicker towards the proximal end where stress is highest. There, it is made of 5 members:  4" and  2" high aluminum boxes, and  aluminum bars. When the crane is loaded, these members experience significant shear stresses which try to "shear them apart". Epoxy joinery was used to hold them together. (see sequence below). Once the epoxy sets, the bolts do little work, only preventing the initialization of a "peel failure". Although I was initially skeptical about gluing structural elements together, under the right circumstances, it works very well - even aircraft like the Boeing 787 are glued together.
This design has pretty large areas of planar contact, so epoxy joinery is appropriate. The worst case shear stress on the epoxy is calculated to be 63psi, which is many times below observed holding ability.
Work holding plate can rotate on trolley. Trolley has Delrin bearings and, once slide-locks are loosened, can slide 4 feet on aluminum box beam.
The connection between the jib crane and the vertical column must withstand about 5000 psi of bearing stress, yet still pivot and slide easily. The oilite bronze bearing does a great job here.
The crane vertically "self locks" - it wont slide down the column by itself.