Observatory base ring sealing.

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24th Jan '19. Despite it staying at 24-25F, -4C outside and heavily overcast I have been working on making arcs to add to the top ring. There are crescent shaped gaps between the skirt and the top ring where the rotation rollers sit. The gaps have allowed the wind and rain to blow into the dome.

The first image shows one curved addition from the outside. The heavy, 1.6mm EPDM skirt has been lifted out of the way to show the joint with the octagonal top ring. Which was constructed with 2x8s laid flat on top of the 4x4 full height posts.

The dome is 16 sided while the top ring on the building is eight sided. There will never be a perfect match between them but the rubber skirt can adapt to such variations if I make the ring as round as possible on the circumference. 

The view from the inside of the dome. Note the domed, aluminium, roofing washers to spread the loads into the rubber skirt. Hopefully this will avoid the fixing bolts tearing through the edge of the rubber over time.

 I used a 1.6m radius bar to mark the curves out of lengths of 2x4. While I could have nested the curves to save on materials I was using the bandsaw to cut them out. Which meant that I needed shorter lengths of timber to be able to handle them comfortably.  I could have used a jigsaw but on 2" thick material the blade can easily wander. 

I ran the curves across the 12" disk sander to tidy up any saw marks and produce a well rounded edge. The curves are each drilled 4" from each end ready for the 75mm [3"] Torx CSK screws which will hold them in place.

I was able to finish all eight curved lengths and screw them to the top ring. There is hardly any wind today. So I can't make a proper comparison with the former, very draughty conditions inside the dome. There was so much clearance in some places that the rubber skirt would slap noisily against the base ring when it was breezy.

The dome was given a quick spin, using the drive crank and 4" friction roller. This showed that there was no increased resistance to turning the dome due to skirt friction with the new timber. Snow is forecast and I didn't want a dome full of spindrift. So this was a good time to close off as many gaps as possible before the event.

Click on any image for an enlargement.

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