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Yesterday I tied the first cross brace into the south-easterly post of the octagon. The same should occur at the rear but I need to raise a 4m post there first.
The octagon's joists continue to try my patience. They are essential for secure fixing, but getting a saw at them, just to clear the cross braces is proving a trial.
I have started using a 5A battery with the DeWalt drill/screwdriver. I was getting tired of descending from the building every five minutes to replace the 2A battery with a newly charged one.
More progress today. I raised the last 4m high post in the NE. First it had to be run through the table saw to make a chamfer. Then I tied the upright into the octagon post with a 2x4 cross brace and bolted the twin posts near the top.
Fitting the other cross braces to the same NE octagon post would require removal of the plywood cladding. An exercise I am leaving until last. To avoid letting the rain in. The majority of the new cladding has to be in place first. Not to mention having the new dome on top to keep the rain off the interior.
I am trying to measure the diameter of the new building by lifting the old, rubber skirt. From cross brace, flat to flat, it looks like 4.1m Ø using tape measure. The outside diameter at the posts is far more important. Since it scribes a larger circle and clearance from the dome's inside skirt is the vitally important measurement.
This is without the plywood top ring being fitted. Which will support the rollers and stiffen the top of the building. I will try measuring again later but using the laser when it is slightly darker. This improves the visibility of the red, target spot to avoid making mistakes. [4-4.1m in diameter across several diagonals.]
I should also use the green 360° laser to check the level of the cross brace, top ring too. That will need a spacer block because the cross brace ring is slightly lower than the octagon's, 50mm thick, timber, top ring. [There was a 12mm [½"] variation in level around the top brace circle.]
The grooved, plywood cladding is available in 9mm and 12mm. I used the 12mm last time. The saving between the different thickness of sheets is not astronomical. Though it adds up when at least 18 sheets are needed. I am now seriously considering making the structure much stronger but using only the thinner sheets. [9mm]
I could clad the inside as well as the outside of the upper building [at observatory level] for a sandwich construction. There is quite a wastage on the exterior cladding due to the width of the exterior panels [frames.] The sheet width is 122cm. Where I need only about 80cm width per panel. 42cm spare would easily cover the inside panels by using two vertical strips per panel.
The sheets are supplied with handed, halving joints on each long edge. So the gaps are intended to overlap and would go unnoticed. Making the observatory much more attractively finished inside. Rather than having only the inside of the inferior B/C quality ply and the cross braces visible. Not to mention requiring painting to be cosmetically acceptable. Matt black paint is not cheap and quickly went mouldy last time! Something to avoid.
I could, of course, use the "waste" material to help clad only the outside for a smaller saving. Though this would not be as strong as using a full sheet per panel. Particularly since I am relying heavily on the stressed skin effect for increased, structural stiffness.
Adding rigid [?] insulation is an option within the sandwich construction. Since I use only screws for fixing I can easily remove the inner cladding later. If I should decide to insulate.
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