5.04.2021 Wintry weather stopped play!

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Monday 5th 32F, cold and windy with wintry showers. We have had several, short-lived blizzards! An odd day of highly changeable weather. Overnight gales were forecast. So I loaded the windward side of the spare segment leaning against the dome. I didn't want it wandering away in the night! Foam packing separates the segment from the dome.

I need to cut a lot of 1.5m wide, 12mm birch plywood arcs with long radii. [2-2.15m]. To make laminated, slit and shutter ribs and the base rings. I'm thinking of using a router with a small, solid carbide, spiral bit. CMT in 6mm? [1/4"] 

There are a lot of arcs to cut and my Bosch jigsaw couldn't follow a horse across a field. Putting it on a radius bar [trammel] would be a sick joke! Will a decent router bit stand up to cutting countless metres of birch ply? Even several router bits would be much cheaper than buying a new and better [?] jigsaw. So I have ordered 6mm and 8mm spiral router bits by CMT. A quick check online showed that every "Best of" reviewer had a completely different, favourite jigsaw! 

Designing the slit and shutter ribs for my dome is not as straightforward as "normal" 2D, bi-parting shutters. The shutters will be cut from the centre of the spare segment. Which has a full, spherical curvature. Along with the added complication of a "faceted" surface, the shutters will also be "handed." [i.e. L&R]

This means that the shutters will be deeper where the shutter ribs meet at the centre of the observation slit. While remaining shallower at the edges. Where they meet the slit ribs for the outside seal when closed. The outer shutter ribs will have to be chamfered to fit inside the shutters.

The idea is to maintain the lowest possible projection. If only to reduce wind effects, including drag, torque and turbulence. Particularly when the shutters are at right angles to the wind. Note that the shutters will have the same radius as the dome but will be outboard of the dome's surface. Which would normally require a larger radius.

The closed shutters will also look much "smoother" if they do not project too far. Though there is a minimum projection for the slit ribs if a good seal is to be obtained with the outer, shutter ribs. Perhaps this seal could be augmented with draught excluder? I have not shown the central, shutter overlap strip in the drawing. This usually helps to keep the rain out of the closed shutters. At the expense of a slight loss of open, observation slit width.

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