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Friday 15th. Finally, I am the proud owner of eight x 12mm x 1.5m x 1.5 sheets of birch ply to make ring templates. I'll start at ground level. To mark out the correct radius of the foundation blocks. The ring will then be lifted in sections. To be rejoined at the top of the expanded building to confirm the radius up there. I can then check the uprightness ready for the 2x4 vertical posts. Nothing will be wasted. The template rings will later be laminated to make a solid top ring. Which will support the dome's rotation rollers. It will probably be too cold to glue anything for a couple of months.
Removing the original building cladding, to mark out the radius from a new centre point, might have worked. It was just not very sensible in the middle of winter. Not to mention the time-wasting removing all the fixing screws. Then replacing them again afterwards.
I can soon begin to tootle along. Burying the new blocks in a ring at my own pace. Without the templates I had no easy way to set out an accurate circle. One which will based on the two posts nearest the shed. These will remain untouched and anchor the new building's footprint. With a slight, South Westerly bias to the ring compared to the original.
These two, octagon posts are 120cm apart. So slightly more than the spacing of the 12 others I intend to use on the new building. More posts means more foundation blocks. Which must mean greater building strength, mass and and stability. Particularly in resisting gales. Apart from their own weight, 35kg, the foundation blocks are deliberately tapered. This helps to resist lifting out of the rock hard, self-compacting gravel. The larger footprint, at the bottom, provides a larger area to resist sinking under load. The more the merrier.
There really is no point in digging up the two, easterly foundation blocks. I shall allow the template to butt against them rather than passing well outside. The outside of the new top ring will then fall just within the radius of the original octagon's top ring. The error of post placement [for these two] can then be safely ignored. The new, top ring will pass safely over the top of the old.
The remaining [new building] circumference can then be simply divided by 12 to discover the new post spacing. The entire building's radius must fall within the dome skirt. To ensure the run-off provides natural weatherproofing. Though a skirt of some sort will be required to cover the considerable height of the rollers. Though these could be "lost" to some extent to reduce the considerable gap between the building's top ring and the underside of the roller ring on the dome.
If any of the original [octagon] posts can be safely removed then so be it. They support the octagon's floor joists. So still have a vital part to play if the joists cannot be directly and structurally tied into the new building's upright posts. The new posts will all be joined in securely. Though it may not be easy to make them all equally load bearing. The position of the new posts is dictated merely by their geometry on the circumference of a fixed circle at equal spacing. Which bears little relationship to the present ends of the octagon's joists.
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