7.05.2021 Brackets in quantity.

 *

Friday 7th 44-50F, overcast and cool. Soon turned to sunshine. None forecast. There were a few light showers and some sunshine but it was after lunch that the sky turned black to the north. I was too hot working in more than a T-shirt in the sunshine.

I have received the parcel containing 6kg or 60 brackets. Overnight delivery after ordering yesterday. Some businesses are still efficient and capable. With PostNord now delivering reliably. Other businesses are still using the virus as an excuse for gross inadequacies. Lies about stock levels and a roundtoit bag of immoral ethics when it comes to restocking and supply. 

No excuses for me now. I shall have to start making ribs and bolting it all together. I can see it in my head. Having mentally rehearsed the steps and mistakes endlessly. I'm a biological CAD who runs on morning muesli and marmalade on toast. 😋

I spent most of the morning arranging the shutters to bring them up to a sensible height and the correct orientation. [Sideways tilt at the top to follow the dome.] The fibreglass panels are flexible enough to follow any desired radius along their length. So I need the ribs' outer curve to be cut to that new radius. The dome's slit ribs will be half way in and half way out of the 4.3m shell. So I'll need to know the inside radius as well. Just so that the ribs and shutters faithfully follow the dome.

I used 2x4 [50x100] off cuts, on edge, to support the shutters inner edges concentrically with the dome. I would prefer less thickness, for a lower, shutter profile, but the zenith board sets the minimum height. The curvature across the shutters means the outer edges are lower than a normal bi-parting shutter.. Whether the shutters are open or closed.

The last image [below] shows the view from the back of the dome. The white line is drawn in to show the need for a minimum height for the shutters. There must be a close fitting, protective, weather cover for the drawer slides when the shutters are closed. The slides also have vertical depth so must safely clear the top of the dome. 

This mock-up is turning into quite an exercise. I have tried various packing thicknesses but still need more. Otherwise there is no room for the 6cm depth of the slides on the outside of the zenith board. 

The long board I used to support the tops of the shutters is actually too long. So it won't let the shutters droop far enough laterally. So the shutters are not concentric with the dome laterally. Which makes them much too high on the outside edges. This also throws the edge geometry of the shutters out of line. They appear twisted or the edges curved. I can't cut the base of the shutters horizontally until the shutters are correctly arranged. They appear tilted.

Could the slides be fitted inside the zenith board for better weather protection? I doubt it. Not if I need to fit large eye-bolts for the pulley system. The eye-bolts would have to be fitted where they don't affect the sliding shutters.I'll have to look into this.

The usual practice is for the top slides to be screwed to the zenith board and top shutter boards. The zenith board also fits half way in and and half way out of the dome shell. I shall scribe a second and third 12mm, plywood board to sandwich the top of the dome. They will beef up the zenith board and spread the loads more evenly though the GRP shell. 

The laminated, slit ribs join the zenith board at right angles. They will be securely fixed together with large [roofing] nail plates. Much as I did with the present, plywood dome.  I use the zenith board to support the pulley system. Which is needed for lifting the large and heavy OTAs on and off the mounting. 

The new dome is slightly higher which will help with clearance problems when lifting and lowering, long OTAs. I would never risk lifting the heavy mounting itself using the pulley system. 

I have plans for adding a gently bent and curved, zenith plate. To be made out of sturdy, 10mm x 150mm [~½" x 6"] scrap aluminium. To closely match the dome's curvature and facets. This would be securely fixed to the zenith board, with more brackets, to ensure more than adequate strength at the top of the dome. 

The observation slit is a very large cut-out from the dome's shell. Which must weaken the structure. Even if the ribs and zenith board help to put back most of the missing stiffness. The zenith plate will be bolted to the inside of the shell and extend out to the width of the top segment of the dome. That is until they reach the moulded reinforcing ribs. 

After another couple of hours fiddling between showers I have decided to make the inner shutter ribs. The ribs can be attached to the inner edges of the shutters with brackets. Then the outside height and curve of the shutters can be checked knowing that the centre ribs are straight and to the correct radius. The radius of the inner shutter ribs will probably end up as 15cm greater than the dome's 2.15m. I can check the required radius by packing up the tops of the inner shutters with at least 6cm clearance above the centre top of the dome for the slides.

*