2018 New Year Dome build progress?

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A couple of weeks into the new year there was an unusual combination of light winds and dry weather. The temperature is still hovering about freezing point.

So I dragged out some dome segments to have another look at providing an observation slit. Two long arcs of plywood and several 60cm struts gave me a basic, slit framework. In theory I should be able to scribe across the horizontal struts onto the segments either side of the slit. Cutting the struts off to the scribed lines should allow the slit frame to be slid into the dome structure and screwed into place. 

However [and there's always a however] the geometry of the mock-up might result in rather inaccurate marking. The slit cannot be physically inside the dome's surface and still miss the segments on either side. So it must be laid over the existing dome segments. Perhaps I should remove the horizontal struts and measure their new lengths and angles after the slit is fitted in place?

While trying to decide on suitable shutter[s] for the slit I originally thought I was going to use numerous shallow doors. With interlocking frames [like trays] for weather proofing.

Then I realized that horizontally sliding, split shutters [Palomar style] would still suit the angled geometry of my faceted [tetrahedral] dome. It would just require that the shutters themselves follows the angles of the tiers of the facets just like the rest of the dome. No doubt the shutter facets would each need to be slightly deeper than the dome because they were being overlaid.

Here's yet another mock-up with the slit frame resting on top of the clamped dome segments.The main problem is that a beyond-the-zenith, cut-out would require shortened ribs. With the result that the [clamped] dome would no longer be self-supporting without the slit frame already fixed in place. Another of those chicken and egg problems.

Then I imagined a square frame carefully supported and centered at finished dome height. The ribs could then be carefully marked and cut away to match this frame. Allowing the slit frame to take its rightful place once the segments are all accurately prepared.

Such a shutter arrangement has several potential advantages: Including improved weather proofing and no small, flapping doors, each requiring secure fasteners. Plus the ability to open one half shutter and leave the other closed for better wind protection.

Rain should run down these full length shutters just as well as the rest of the dome. Without intervening rain-collecting ledges. As might well occur with small doors. If done properly the closed shutters should offer the least offense to the eye as a discontinuity of the overall form of the dome. The overlap between the two shutters would obviously need attention to stop rain from driving between them. The shutters would slide horizontally on stainless steel pipe firmly fixed at the skirt and the over-the-zenith frame.

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