Dome build: Construction access?

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I have already discussed the difficulty of getting any sort of crane in the back yard/garden. Our narrow drive runs very close to the house and is bounded by trees embedded in a tall, shared hedge on the opposite side. The rear view mirrors on my modestly sized car brush the hedges going both ways.

Then I remembered my 5m, 15' roof ladder I had made up after the great storm of '99. When I desperately needed safe access to repair the damaged roof myself, working alone. 

I had bought half of a wind-damaged, two stretch ladder and had converted the good half into a roof ladder with an add-on, ridge hook and wheels kit. Aluminium crossbars bolted on the underside allowed it to lie safely flat on our heavily ridged roof.

I just need to fix a rigid stand-off to the octagon walls for holding the top of the ladder. This will provide safe access to a perfect working height with good ladder width for sliding complete gores aloft. The dome will still rotate inside the top of the ladder. Allowing single gores to be safely added at each station as it rotates. Scaffolding would not have helped much because I'd still need to get the gores up there somehow.

Needles to say my new strut lengths were totally wrong! A recalculation showed that C3 should have been 36 not the 51.5cm of which I had just cut another 14 examples! Despite three gores fitting nicely, side by side, the new dome went together in a huge spiral! Eek! 😨 Wrong again!

Finally, I decided to trust the trigonometry which required a re-measure of a full gore to be safe. This confirmed my original measurements for Radii and the altitude angles of the struts were correct. I even used several different methods to check and all the numbers seemed to confirm each other.

Running through my "sums" again showed I had made some silly errors of entry on my calculator. Or made 'typos' onto the computer drawings. So the longer C3 struts had to be shortened again. To 48cm not 36! Though the 40cm C4 top struts still seemed not to fit well. Regardless of all this, I still managed a half dome which fitted together and had the correct diameter and height. All the ribs now lay flat against each other without obvious strain and needed far fewer clamps. So, progress at last? We shall see when I get a full dome, with full length ribs, clamped together. Until then, your guess is as good as mine. It's all been taken apart again and gone under the tarpaulins overnight. Two days of rain or showers are forecast.

Click on any image for an enlargement. 

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