Tubing: Altitudinal Mechanisms – Failure followed by success

Now I turned to the smaller finished piece of African mahogany. I realized I could cut the board into narrower strips and bolt them through the exterior of the tube into the interior baffles. Trunnions could be affixed to them. After cutting two slats of two-inch width from the board, I routed out, also lengthwise, a half-inch wide, quarter inch deep mortise into each of which I laid a two-foot length of t-slotted curtain mounting track that I had found at the local hardware store. I then took another two of the 11” disks of African mahogany and cut a corresponding mortise along their diameter. I drilled a center hole in each and reinforced it with a plastic separator. A bolt with a hexagonal head could be slipped into the mounting track and the wooden disks set onto the bolt. The round knobs are in fact decorative nuts that can be tightened and loosened so that the trunnions can be slid forward and backward along the mounting track, and thus be adjusted according to where the balance point of the tube is. The mortise in the discs aligns as well to the mounting track and so adds stability. Later I determined that the two disks (the trunnions) did not remain consistently parallel to each other and that it was tricky to ensure they were at equal points along the mounting track; so several weeks I took the remaining slat of African mahogany, cut it to the appropriate length and used it on the underside of the tube to hold the disks at a steady, parallel distance from each other.


The mahogany strip is screwed into the two plywood baffles inside the tube that give it its octagonal structure. The curtain hanger (painted black) is sunk a quarter inch into the mahogany strip. The hanger is held in place by two screws.


Here are what I am calling the trunnions. Notice that I routed out a mortice that slides along the curtain hanger. Notice the hexagonal bolt that also will run through the curtain hanger. The black knobs tighten and loosen the trunnions in place.


The beam holding the two disks in place ensures that the trunnions remain vertically parallel to each other when mounted and that they remain equidistant along the length of the tube.


The tube with trunnion slide: this contraption allows me to slide the trunnions along the length of the tube and so balance the tube according to its center of gravity on the mount.



Here you see the trunnions mounted on the tube and the tube resting on the mount.


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