31.07.2021 Shutter rib height problem.

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Saturday 31st July 62F. Windy and overcast. Showers. Possibly thundery, heavy showers later.

Yesterday's effort to install the central shutter ribs showed up a problem. The straight, centreline of the shutter covers was slightly bowed. The outer ribs are too low relative to the central ribs. Or, the central ribs are too high. This has the effect of rotating the individual rectangles of the [spherical] shutters. 

While I prefer the lowest possible, shutter profile, I am limited by drawer slide clearance. Which must miss the undersides of the outer edges, of the tops of the shutters.  I shall have to check the slide clearances before deciding which ribs to adjust. The ribs projecting towards the camera in the image are the slit ribs. Not the shutter ribs. Which are hidden behind the zenith board.

It turned out that the central, shutter ribs weren't exactly straight. In my haste to protect the dome innards from the threatening rain I hadn't fixed the base of the central ribs. So I removed the shutters again to be able to check the ribs with a 2m straight edge and tape measure. I was 2cm out at the bottom of the ribs. So I hammered some angle iron into the ground to fix the base of the ribs.

The image [Right] shows how I access the top of the dome. A large concrete slab rests on the ground to stop the base of the ladder from sliding out. Three slabs in fact. One each at the sides and one at the back of the dome. With two ladders available this saves an awful lot of ladder movements.

The lengths of pipe insulation are both very resistant to compression and have very high friction. Ideal for maintaining the ladder safely on the dome. Without the risk of it slipping sideways or marking the dome. The orange ratchet strap has been exposed to the sun for months and has lost its brightness. It is hooked under the dome skirt on opposite sides and holds down the shutters.

It started pouring again as soon as the shutters were off. So I have stapled a scrap of clear, net-reinforced tarpaulin over the tops of the ribs. I should have done this earlier but didn't have enough material to cover the entire slit. Or anywhere near it. Now there is plenty of light but not enough shelter. 

I found another piece of clear tarpaulin and covered the lower part of the slit. A storm warning for thunder and cloudbursts has been issued. Though nothing so far. Which gave me a chance to tidy away the ladders and tools.

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