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Thursday: Another wet and windy day forecast. If it stops raining long enough I can start adding vertical struts to
the sides of the ribs. No glue. Just screws for the moment. The
tarpaulins have to come off to add more structure. The table saw will be
used to cut the struts on the diagonal.The dihedral geometry of the outside angles should take care of itself. Provided [of course] I get the strut material dimensions correct and lay the hypotenuse side of the triangular cross section on the ribs. The struts need to "lean away" from the ribs. To allow the covering panels [trapezium facets] to lie flat and well supported on all four edges.
I still haven't decided on the best method of cutting the plywood ribs away to match the 'tiers' of covering panels. It may be best to mark the ribs using the vertical struts as straight edges. Then remove the vertical struts again while I cut the paired ribs with a jig saw. Only adding the vertical struts after the ribs are modified.
The problem is the horizontal ribs will get in the way of the body of the jigsaw. So that needs serious thought. Particularly considering the sheer number of straight cuts to be made. [4x32 = 128!] I don't want to have to remove all the horizontal ribs as well. That would add considerably to the work to be done when all the horizontal struts must be multiplied by 16. Or [rather] 15 with the strut-less observation slit included.
The quickest way may be to separate the gores/segments after marking. That would allow the jigsaw to work from the sides of the ribs unhindered by horizontal struts. Though the straight lines would need to be carried over to the bare sides for the saw blade to run along. A small hole drilled at either end of the original lines would do. This would provide an accurate guide for re-drawing the lines on the bare [joining] sides of the ribs once the segments are separated. I can run a coarse sanding disk along the sawn edges of the ribs to tidy up once all the vertical struts are all re-fixed in place and the gores re-united.
I know I tend to talk each step of the construction [almost] to death. But the sheer number of elements [and cuts] involved must be taken into account. The potential for massive time-wasting is enormous. Getting something wrong 128 times and having to start all over again doesn't even bare thinking about! Most of the endless text is for my own benefit and to remind myself why I chose to do something that way.
Better [surely] to waffle on [and on] and do it right? Rather than barging on and making endless [creative] mistakes. Improvising on my projects could have very serious financial consequences if I do screw up. Wood and birch plywood, in particular, doesn't grow on trees!
It soon became obvious that the tarpaulins weren't doing much good as they flapped wildly in the wind. I had criss-crossed the dome with cords but it wasn't really helping. Then it started spitting with rain so I did a quick removal of the tarpaulins and moved the segments back into the octagon. Where they were covered in several smaller tarpaulins. I'll have to enquire whether dome building and dismantling can be added to the Winter Olympics.
Now I have added a hefty but inexpensive, cast iron, 30cm/ 12" disk sander to my toolbox. This will be handy for quickly trimming the compound miters on the ends of the vertical struts when I'm building the dome. The struts should all be the same length. Making me wonder whether I should deliberately make them so. Then adjust the horizontal struts up and down to achieve a perfectly uniform structure. The more uniform the skeleton the more uniform the plywood cladding panels can be. Mass production with accurate machines has enormous benefits for time saving. Making lots of components individually can introduce endless errors and prolong the build for months.
Click on any image for an enlargement.
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