Dome build: Shutters: Getting closer.

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Sunday: The amount of work achieved today could only be measured on the Imaginary Scale. I did cut out another pair of half ribs to make a whole one. Then I clambered about on ladders pretending to adjust the projection of my tentative new shutters. But which, in reality, meant two roughly sawn arcs were clamped into various places before standing back to admire the situation from the ground.

Until I have my drawer slides in hand I can only guess as to their size and likely position. So I daren't cut anything or make any fast [slow] decisions. I thought I had discovered that I can play about with  the degree of projection to personal taste.

At first glance it does seem only the depth of the cross battens really sets any minimum projection limit. But, if I make the shutter projection too little the outer shutter ribs will hit the dome much earlier rather than later. Which means they would be too thin and weak by the time they had been cut back to clear the dome. So, with this in firmly in mind I shall not make shutter projection too little. I think it best to build a complete shutter to see where it hits the dome.

I also made a pair of test bars to ensure I understood the width of the shutters without having to do any serious maths. I cut a batten into two and nailed some 12mm plywood scraps to both ends of each. These proved that my shutter ribs would indeed stop and start where expected against the actual slit ribs. Then I tidied up early at the sight of a large blob of rain on the radar image on the DMI's weather website. Another case of vivid imagination! It stayed completely dry.

Monday: My new cartridges of brown Sikaflex 591 have arrived and the drawer slides have been dispatched. I still have some internal reinforcing to do at the top of the dome. It is very awkward to reach from the internal stepladders and I am still getting dizzy when I tip my head back.

The images show my trimming of 1/2 ribs for the shutters/doors with the router fixed onto a stiff radial arm. The two splayed boards form an A-frame and are steadying the outer sections of each rib.

I found it best to leave the beam pivot in place and simply adjust each new rib close to the cutter. I then fixed the arc firmly to the splayed boards with csk head screws. Checking both ends of the arc against the cutter before starting each time ensured concentricity and nicely even cuts. The little Makita router is a great tool for this purpose compared with my other two, full sized routers. Their sheer size, weight and poor visibility would have greatly hindered progress. The smart little Makita can be simply lifted up on its aluminium arm with one hand and swept back to the beginning of the arc.

The eight half ribs had been quickly cut out with a jigsaw just outside scribed lines drawn with the DIY beam compass at 1.5m and 1.65m. I used a pencil for this but should really use a ballpoint pen for a nice sharp line. I am always afraid I will mess it up somehow and leave an indelible record of fact.

This method made router trimming effortless and very quick compared to cutting out the arcs from full sheets of ply with the router. I was very pleased with the way this job went. Shame I was never able to use it on the dome ribs. A higher degree of precision and repeatability would have worked wonders on the dome.

Every minute I spend on the woodwork version could have been far better spent mass producing components for a far more perfect, all aluminium, trapezium dome. Which would be notched and bent without any welding or rolling into impossible 3-dimensional curves. Simply nuts and bolts to hold all the straight lines together. To be covered in flat sheets of aluminium neatly bent at intervals from top to bottom in single lengths.

Click on any image for an enlargement.

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