7.08.2021 ADHD and the fine art of dome building. 😎

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Saturday 7th 58-72F. Overcast with occasional sunny periods.

I discovered variations in the lengths of the tops of the ribs yesterday. This caused misalignment between the zenith board and the tops of the shutters. This must be attended to before I can start fibre-glassing. Once they match at the top I can attend to the bottoms. A carefully levelled plank, long enough to carry the loads of the open [and closed] shutters, will give me a base line reference. 

Until now, the four shutter ribs have each been resting on separate stacks of packing material. Opening and closing the shutters yesterday became a tug of war between the lower ends of the ribs. I had to resort to levers, adding more material, or sawing off strips. Fortunately the shutter ribs are still far too long at the bottom. They project well below the intended base ring height. I have been very conservative about trimming them so far.

All of these problems are the direct consequence of having spherical, shutter covers. The shutter ribs ought to be vertical at the bottom. Since the shutter ribs are parallel to each other this gives me a clear indication of their level of support at the bottom. 

They were anything but vertical when I started. This bow-legged appearance showed in the lateral curvature of the ribs away from the fixed, slit ribs. The shutters are very sensitive to the height of support at the bottom of the ribs. Quickly adopting a lean relative to the slit ribs with any error. It is a simple matter of amplification of angular displacement by leverage.

I am glad I arranged the open shutter mock-up. It gave me a far better insight into the geometry and some glaring errors. Imagine fitting the drawer slides and then  having to undo all my previous work. Just to correct the rib lengths. With the slides out of parallel the shutters would have been badly askew. Making opening and closing a nightmare!

I suppose I could have built the woodwork first and mounted it on the dome. Then draped the spherical GRP shutter covers over the ribs. The problem was my understanding, or rather lack of, the geometry of spheres. It is sixty years since I sat through a class in geometry or trigonometry. Whether any of it was relevant to my immediate problems is lost to having the [lifelong] memory of a sieve. 

I couldn't remember a lesson ten minutes after the event back then. So I certainly would not recall anything now. Imagine having to reinvent the entire world from scratch every single day. All depending on the particular challenges I face. Life would be so much easier if I didn't keep setting myself these complex but ridiculous tasks. Having had dozens of hobbies and countless hundreds of interests does at least give me a rehearsal for whatever crops up.   

Progress: I had to cut back the tops of the shutter ribs to match each other. Also allowing the zenith board to move inwards. Which provided me with more shutter overhang. This is needed to make room for and to protect the drawer slides from the weather. The two shutters had ended up with different overhangs after repeatedly trimming the ribs at the bottom. 

Meanwhile, the metal, fixing brackets were forcing the shutter ribs out of square. Which gave me the opportunity to remove all the brackets and bend them all to a better angle. Which then allowed me to lift the GRP cover by the necessary distance. Which simultaneously matched both the top overhang and the bracket bolts. The bolts had moved downwards on one shutter relative to the other. Now they are all back at the same level. I also have a length of 2x10 made level on the ground under the base of the ribs. So that's another hurdle overcome.


Now I want to open the shutters again to check their alignment. Unless they are open I can't see. Nor measure the structure at the zenith. Just reaching the zenith from a ladder, without depressing the dome with my own weight, is impossible. So examining this area from the internal stepladder is vital. I have been using the roofing square, 2m straight edge and builders levels to check, where possible. The tops of the shutters are out of sight, beyond the zenith board, viewed from inside the dome.

I fitted the slotted angle iron across the top of the dome and under the shutter ribs again. A couple of 6" screws kept the angle iron secure. Otherwise it wants to escape as I tug at the shutters to open them.

The 2x10 ground board proved to be far too thick. The shutters would still not drop far enough to be concentric with the slit ribs. So I used a 1" thick plank instead. There will need to be more rib trimming tomorrow. It was nearly 20.00 before I finally gave up and went in for dinner. I left the shutters open overnight to save some time in the morning.

 

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