Spring has sprung the dome is ris[en.]

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As it was hovering around 60F [15C] I decided to make another start on the dome. The last time I tried to glue anything it turned snowy white and didn't hold. So I put off further work until the spring. Since I have to work out of doors the long cold winter has delayed progress more than I would have liked.

First I had to take down the dome base ring which had been leaning up against the octagon building over the winter. All the screws had to come out again to allow the two layers of birch ply to be separated.

Then I applied a line of fresh construction adhesive at each adjoining edges and a wavy line in between, to each lower arc. The second layer was then laid on top and the two screwed together. Followed by all the clamps I posses. I then added further 25mm [1"] screws to ensure it was all as solid as possible.

The forecast is for only 41F [5C] overnight so I shall lift the ring off the ground on wooden blocks and cover it in several layers of lightweight tarpaulin.

Or not. I was keen to frame out the observing slit on the  dome. So went ahead and rebuilt and clamped the dome. The frame of the observing slit is 60cm [2'] wide and overlaps the zenith.  The cross strut is only temporary to ensure the slit remains square and the correct width.

Now I see the frame in place I realise that I should have made the ribs twice as deep. Just to have something to which to firmly attach the normal ribs for strength. Not to mention closing off the dome against the weather on either side of the frame.

Originally I was going to have an up and over shutter but then decided to go with small overlapping doors. The faceted sides don't really suit a bi-parting shutter. Horizontally hinged doors seemed the only way to build a shutter which closely matched the rest of the trapezium, faceted dome.

Perhaps the shutter could still be made flush with the dome rather than projecting? Though I don't see how the hinge gaps could be safely sealed. If the slit frame is projecting then the hinges and the edges of the doors can overlap the frame to form a seal. A sponge draught seal strip will help here.

Tuesday 10th April 55F and gales. I decided to cut the flats on the gore ribs. The shorter gores went quickly enough: 10 x 2 x 3 flats. Plus 3 full gores of 3 x 2 x 4. The image left shows the stack of short gores already cut. The three full gores have yet to be taken down and cut. I use these three to support the dome while I am putting it up.

In fact all the gores are identical except that the short gores have yet to be extended beyond the limited sheet width from which they were cut. The wind makes the sawdust fly everywhere despite standing with my back to the wind. It is exhausting to spend so many hours out in it.

Wednesday 11th, 50F, Sunnier but just as windy. Finished cutting flats on the outer edges of the ribs for the covering panels. For some strange reason the dome now looks smaller. Perhaps the eye can more easily lock onto the flats than it could with more featureless curves?

I had planned to cut vertical braces with inner slots [dadoes] to lie over each pairs of ribs. This would provide greater strength against vertical crushing loads like snow and very strong winds.

Thursday: Decided to cut side mounted profiles on the table saw. By cutting on a miter I was able to obtain the correct slope for each gore at one cut out of 18mm x 90mm. 

Click on any image for an enlargement.

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