20.08.2021 Zenith boards: More reinforcement.

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Friday 20th 64F, mostly overcast in the afternoon. I visited a builder's merchant for more bracketry. 

Two hefty brackets now join the tops of the slit ribs with the lower zenith board. It may look a bit untidy to some eyes but it will eventually be painted. I could have duplicated the 4"x8" hole plates but it already looks like overkill. I can easily change my mind later. It takes only moments with a rechargeable drill-screwdriver.

I bought some hefty angle brackets for the connection between the shutter boards and the tops of the inner ribs. The problem is the width of the brackets exceeds the width of the ribs. If I add packing material to the inside or outside of the ribs it will strike the slit rib when open. Or the packing on both ribs will come together when closed. Which would force the shutters apart by twice the packing thickness. I will have to rethink this arrangement. Longer, thicker and narrower brackets make much more sense. 

I checked the shutter rib distance [at the bottoms] from the centre back of the dome. There was an error of a couple of centimetres. So I dropped the foot of one rib to match the other's distance. I'll have to keep and eye on this as I finally trim the ribs to rest on the base ring.

It remains a complete mystery to me why I faced the slit towards the hedge when I set up the dome. I cannot get far enough away for photography even with a wide angle lens. It would have made much more sense to face the shed doorway. 

It is much too late now. Rotating the dome on its blocks would be very hard work. I also have fixed posts supporting the ribs and the dome. Moving those would be both a nuisance and a serious time waster. Another incentive to finish the job quickly! Preferably before winter intervenes!

I have now removed the shutters. To allow access to the outside of the slit ribs for glass-fibre bonding to the dome. I used inclined ladders [as shown above] to gently slide each shutter down to the ground. 

The weight is just manageable. The ribs added their own weight but the increased stiffness made the job much easier than before. The naked shutter covers were so flexible [and heavy] that they were difficult to manage.

This final image shows where the joint needs to be glassed over. This will further stiffen the dome and hopefully make the joint fully waterproof. Being above the dome it will not rely on adhesion for strength. As it did on the underside.

I am tempted to run a bead of silicone sealant long the narrow joints between the slit cut-out and the ribs. It's not as if the glass matt [CSM] likes being forced into a sharp 90° anyway. So the silicone can fill the gap and rest on top of the glass fibre bonded to the lower side of the slit rib. 

First I must abrade the dome where the glass mat is to be bonded. To provide a proper key. Adhesion to the glossy gel coat would be poor without this extra work. Though it feels very wrong to be sanding the smart outside surface of the dome. I must remember to add the green colouring to the lay-up resin. To help to reduce the visual impact. I shall do the fibreglass work from the comfort of a stepladder inside the dome. Which also relieves the dome of my weight. Thereby avoiding unnecessary distortion. 

I also have to fibreglass the zenith board to the top of the dome. Not easily done with the slotted angle screwed to the zenith board. I will just have to remove the angle iron and use guy-lines on the tarpaulin.

 

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