27.07.2021 More arc and rib making.

I made good progress cutting out and trimming ten more arcs for the centre, shutter ribs. It has become routine. Mark out the arcs on a  fresh sheet of 12mm birch ply using a prepared plywood pattern. [Finished arc] Reduce the spacing between the arcs to a minimum.

Then use the jigsaw to cut in the centre between the marked lines. So only one cut is required instead of two. I use a spring clamp to support the half cut arc with the last arc lying flat on the plywood sheet. Otherwise it sags and may even break off before I reach the end.Then I use a 12mm [½"] trimming router bit around the same pattern to cut back to the lines of the freshly sawn arcs. The pattern is always away from me and supports the little bearing on the end of the router bit.

I use 4" G-cramps to clamp the ends of the arc and pattern together. Then slot the pair vertically into the B&D workbench and tighten. Rout one edge and then flip over 180°. 

A visor is a valuable aid to avoid the fountain of coarse and fluffy sawdust throw up by the router. Ear plugs are vital. I am throwing the sawdust onto the bare ground inside the dome. To try and keep it dry to walk on. After several months in the shade of the dome any remaining grass has long gone.

I completed 10 more arcs today but need only eight. 2.5 x 5' arc lengths per rib length. Doubled for strength to 24mm with staggered joints.

I had no short screws left to hold them together while the glue dries. So I have had to put it off until tomorrow. I need many more screws for the base ring too, when I glue that. The arcs are all prepared but I may decide to have three layers for extra strength and stiffness. 

The base ring is the running surface for the dome rotation rollers. So it wants to be flat and stiff. The base ring also helps to keep the dome round. In addition to the moulded rib just above the skirt. The ring also completes the circle across the previous doorway. It also ties in the bases of the slit and shutter ribs. Which are further supported via the rotation rollers. 

What is left of the original doorway, each side of the observation slit, will be filled with the remaining, dome, panel material. These spherical triangles will become structural elements to help support the slit ribs and base ring.

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