21.07.2021 Just checking.

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Wednesday 21st 68F, mostly overcast. No sunshine at all. I have been pondering over possible ways to reduce the height of the shutters above the dome. Aluminium, channel sections could have been glassed in over the top drawer slides to carry the rain away. The loss in height would have been minimal. So not worth the effort. 

I lifted off the GRP shutter covers. Which had been secured, while resting over the observation slit cut-out. Then I spent some times carefully aligning the slit rubs to be parallel with the dome's surface. I ensured that each rib projected by exactly the dame distance above the dome over their entire length. The spacing of the ribs is now maintained parallel by several 2x4 spacers. I then checked the slit ribs were straight with a 2m builder's straight edge.

The 360° laser level was used to double check that the dome skirt was still level. Then I propped up some base ring arcs to check the level of the base of the slit ribs matched the rest of the dome. The green line continued along the base ring and around the top of the dome's internal, horizontal, moulded rib. Above which I intend to fasten the base ring. This will sink the rotation rollers above the dome skirt by roughly 125mm. Allowing a much shorter weather-proofing skirt. Probably an up-stand of thin  birch plywood instead of something hanging down from the dome skirt. Though I may duplicate the skirts for better wind resistance. This can be decided when the dome is in place. I won't risk having a fragile skirt in place during the big lift.

I removed the zenith board and used it as a pattern to mark out further examples. These will thicken the zenith board by further [3x12mm] glued and screwed laminations. I shall add the same, faceted, convex top profile to the 2x4 slit rib braces. This will ensure the shutters rest correctly for checking their geometry and the curvature of the shutter ribs. 

At the moment the shutter covers are only supported at their outer edges on the slit ribs. Which made them collapse downwards at the centre. Which in turn made the centre edges overlap in a deep curve. I know the edges are dead straight when the shutter covers are lifted correctly to match their faceted, spherical profile. They cannot be otherwise since these edges were cut to a straight line from spare, dome material.

Only when correctly aligned and supported will the shutters' inner edges meet along their length in a straight line. I will then know the lateral angle required for the top edges of the outer shutter ribs.  Which must remain upright to close flat against the slit ribs when closed. The central shutter ribs must also be upright of course when brought together. 

Much of this is just re-checking that I haven't made any horrible [and potentially expensive] mistakes. The dome design is all in my head. Which can't always be trusted to keep an eye on every, likely problem. 

I admit that I have been dragging my feet while I wait for inspiration. With none forthcoming the shutters must be built the way I had originally imagined. Though I shall be using lots more GRP for sealing and adhesion of the ribs. Rather than purely mechanical fastening via steel brackets and bolts.

 

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