19.10.2021 Slit base board added.

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Tuesday 19th 55F, heavy overcast but dry so far. Rain promised after 2pm. Continuing for three days.

I have added a 50x200mm [2x8"] board to the bottom of the slit ribs. This will provide the drawer slides with a substantial support. It will also reinforce the slit ribs and base ring. I am using a timber off-cut in case I need to change anything.

The image shows the drawer slides clamped to the front [outer] edge of the board. The 50cm slides are too long for the 92.5cm slit opening. So the inner shutter ribs will need to be notched around the slides. The extra length is then ignored. Being lost inside the shutters.

Then, in theory, I can screw the slides to the slit base board and lower shutter forms. Allowing [again in highly optimistic theory] the shutters to open and close. I do not foresee the shutters being completely effortless without quite a lot of fiddling. 

Reinforcing brackets are optional. Thinner and stiffened with a rib or heavier material without.

I have a fallback option. To use cords and pulleys to open and close the shutters if they should prove uncooperative. I could even use weights to automatically close the shutters. Pulling on a cord would open them. The cord then being anchored to keep them open.  

The plywood dome shutters have performed well until recently. It being quite easy to open and close them from the bottom by pushing and pulling on the ribs. All within easy reach of the observatory floor. I should have reinforced the upper corners but didn't. So one has become loose and allows the shutter to twist slightly. Causing friction. I shan't make that mistake with the hefty GRP shutters.

 

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