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A surprisingly better day than forecast allowed me time to finish the remaining 7 segments. It went quickly enough when I used the countersinking pilot drill. Then drove all the screws half way through before entering pre-drilled holes and fixing the struts. It's the sort of job you get better at just as you finish.
The image shows the result of having all 16 gores/segments to play with. I had yet to confirm the true height as lunch intervened. A short shower of less than two minutes teased me half way through.
The spare arc from the base ring will join another to test the curve's full height over the pole. With all sixteen gores connected by the horizontal struts there isn't much room for error. The dome becomes far too stiff in all planes to allow much flexure.
The stepladder shown here is 1.5m [5'] tall at the top rungs. Which is the correct height for the inside of the finished dome. I laid an alloy plate on the top rungs to give me more area on which to rest all the extended ribs.
I'm calling this one "Total chaos!"
Unfortunately it soon became a total mess. This was because the base ring radius and length of the spare arcs changed from one segment to another. Spring clamps were flying off everywhere as I tried to add new rib extensions and pull the segments outwards. Short, sharp showers did not help.
There is only one way I can think of, to sort out the dome's height issue. I shall just have to cut some more 9mm [3/8"] rib arcs. Then make each rib its correct length to just reach the pole. Only then can I check if the dome's geometry is true. It seems a waste of expensive plywood because the arcs have no need to reach the pole due to the large [2' wide] cut-out of the observing slit. However, I can always use any extra arcs for reinforcing the rib lap joints later. The weakest part of the dome will be the upper sections during snow loads.
The forecast is even worse tomorrow with high winds as well as rain. It was horribly wet but not very windy.
A dome which fails to reach the correct height can be physically raised to give more headroom. Using taller walls or even a much thicker base ring. Which both amount to the same thing. Or, the gores can be slightly expanded as they rise to stop them meeting at a point [the intended pole] which is much lower than planned. The horizontal struts can be pushed upwards to achieve this at the cost of taller, upper panels. The alternative, if the panels must remain as designed, is to cut longer struts and keep those at the same height.
The dome shrinks when hastily clad in a lightweight tarpaulin for yet another, heavy shower.
There are slight advantages, for myself, regarding perspective with having slightly taller, upper panels. My low viewpoint inevitably shrinks the upper panels as seen from the garden below. This is because the dome is lifted, higher than usual, on a low 'tower.' Moving the struts upwards, towards the pole, will save me the cost of replacement materials and the time in cutting all new lengths. First I shall have to make the upper rib extensions to see exactly what is needed.
I am referring only to trapezium paneled domes here. Conventional, gored, hemispherical domes are affected in similar ways. Though the horizontal struts do not dictate physical bends between dome panels. Normally the gores would be sheathed in continuously and smoothly curved sheet material as far as is possible to avoid horizontal joints.
Thursday 5th October: Heavy, continuous rain this morning so I tidied the shed/workshop. I need to be able to work outside on the dome to have enough space to move.
The stepladder shown here is 1.5m [5'] tall at the top rungs. Which is the correct height for the inside of the finished dome. I laid an alloy plate on the top rungs to give me more area on which to rest all the extended ribs.
I'm calling this one "Total chaos!"Unfortunately it soon became a total mess. This was because the base ring radius and length of the spare arcs changed from one segment to another. Spring clamps were flying off everywhere as I tried to add new rib extensions and pull the segments outwards. Short, sharp showers did not help.
There is only one way I can think of, to sort out the dome's height issue. I shall just have to cut some more 9mm [3/8"] rib arcs. Then make each rib its correct length to just reach the pole. Only then can I check if the dome's geometry is true. It seems a waste of expensive plywood because the arcs have no need to reach the pole due to the large [2' wide] cut-out of the observing slit. However, I can always use any extra arcs for reinforcing the rib lap joints later. The weakest part of the dome will be the upper sections during snow loads.
The forecast is even worse tomorrow with high winds as well as rain. It was horribly wet but not very windy.
A dome which fails to reach the correct height can be physically raised to give more headroom. Using taller walls or even a much thicker base ring. Which both amount to the same thing. Or, the gores can be slightly expanded as they rise to stop them meeting at a point [the intended pole] which is much lower than planned. The horizontal struts can be pushed upwards to achieve this at the cost of taller, upper panels. The alternative, if the panels must remain as designed, is to cut longer struts and keep those at the same height.
The dome shrinks when hastily clad in a lightweight tarpaulin for yet another, heavy shower.There are slight advantages, for myself, regarding perspective with having slightly taller, upper panels. My low viewpoint inevitably shrinks the upper panels as seen from the garden below. This is because the dome is lifted, higher than usual, on a low 'tower.' Moving the struts upwards, towards the pole, will save me the cost of replacement materials and the time in cutting all new lengths. First I shall have to make the upper rib extensions to see exactly what is needed.
I am referring only to trapezium paneled domes here. Conventional, gored, hemispherical domes are affected in similar ways. Though the horizontal struts do not dictate physical bends between dome panels. Normally the gores would be sheathed in continuously and smoothly curved sheet material as far as is possible to avoid horizontal joints.
Thursday 5th October: Heavy, continuous rain this morning so I tidied the shed/workshop. I need to be able to work outside on the dome to have enough space to move.
Click on any image for an enlargement.
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