13.11.2021 The shutters lack triangulation.

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Saturday 13th 45F. Yet another, long, grey day in a series. 

It has now occurred to me that rotation of the bottom of the shutter is much the same as lifting the outer shutter ribs. 

I may be able to stretch roofing reinforcement [perforated] strip on diagonals between various, opposed, shutter bracket, fixing bolts. This will hopefully aid triangulation. Where making solid,  shutter, cross ribs is very difficult. Due to severe clearance problems with the slit ribs. I can easily see the GRP shutter covers twisting relative to the shutter ribs. With no real triangulation provided by the covers. 

The deliberate overhangs at the top are becoming distinctly tapered at times. Probably because the tops and bottoms are not performing as if they were the edges of a solid sheet. Which is normally a good way to achieve immense stiffness. So called, "stressed skin" effect. Which relies on the sheet being fixed to a firm framework on all sides. Being spherically curved, to follow the dome, is not helping the shutters at all. 

As soon as I tried to move the shutters today they performed quite smoothly. The trick is to find the midpoint where pushing and pulling does not twist, nor distort the shutters. So the drawer slides can move without being distorted. If the shutters move only at the top, or the bottom, then the shutters are effectively shortened. Which pulls sideways on the slides with considerable force. Which they are not designed to tolerate.

I can probably operate the shutters from the observatory floor using ropes and pulleys. A double pulley fixed to a bracket on either side, inside the dome. Ropes to pull the shutters apart.  A second set of ropes passing though holes in the slit ribs and inner shutter ribs. To pull the shutters closed again. Loops of ropes make sense to avoid tangles. I will want to be absolutely certain that the shutters operate reliably. Before lifting the dome into place. The shutters are far too heavy and awkward to work on high above the ground. 

First priority is to fix the GRP covers to the top boards. This should help to end the shutters' lozenging. There is very little room for brackets to fix them together. Which is why I have been avoiding this exercise for far too long. The drawer slides leave little room on the inside of the boards. There is not enough overlap for exposed brackets on the outside of the boards. 

I had to fit 25mm [1"] spacers at the outer, shutter ribs before the shutters would fully close.

 

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