Dome build: Doors, trapdoor and foot stop.

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Saturday: Yesterday's "storm" was a bit of a damp squib locally but a valuable warning. It was no problem leaving open doorways during the summer but this will have to change if we get wind driven snow. I shall just have to build some weatherproof doors using the same grooved plywood as the octagon.

Both would have to be double doors to be manageable. The veranda door cannot open far if it is not made double. A single main entrance door could easily become uncontrollable in typical windy conditions in such a large size. It is just short of a full 4x8' sheet unless I frame it down to a more normal size. A large door is handy for bringing telescopes in and out. Though this is likely to be an increasingly rare occurrence once I'm set up.

After endless consideration I decided that I would not move the veranda door from the top of the internal ladder. Nor did the double doors need to pass over the top of the trapdoor when it was lying flat on the veranda. The doors would always need to be open to lower the trapdoor outside. The trapdoor will ensure the doors are not closed by the wind.

However, the doors need not be open for the trapdoor to stand vertical. I shall add a couple of small, door bolts to ensure the heavy trapdoor stays upright when needed.

I finally added a length of scrap, alu. angle to act as a foot stop [bumper?] near the end of the closed trapdoor.

The image shows the view over the closed trapdoor from the veranda. Into the pier and across the open gap to the eastern observatory floor. The foot stop is level with the outside of the pier legs where they pass through the obs. floor. This just seemed to be the logical position to have them. Since it continues the natural foot stop provided by the pier cladding on the other three sides. The clearance around the isolated pier is well seen on the far left, 4'x4' leg.

Those who have been paying attention will remember that I climb up the stepladder. Through the hollow, pyramidal pier. To reach the observatory floor, 10' above the ground.

When the trapdoor is lowered flat onto the veranda the alu. angle passes cleanly between the deliberately spaced, larch floor boards. This avoids the trapdoor being propped up unnecessarily. I also avoids damage to the veranda floor by the foot stop. A happy coincidence thanks to careful marking out before the foot stop was screwed down onto the larch trapdoor.

The leaky dome roof is very depressing. Five tubes of marine sealant consumed and it still leaks like a sieve! I have started having repetitive dreams about taping the seams, fiber-glassing and cladding the dome in heat welded tarpaulin. Shrink wrapping plastic doesn't last long enough to be worth the expense and effort. Only shrink wrapping would keep the facets crisp.

The afternoon was spent correcting the shutters. First I lined up the outside edge of all four ribs. That meant a 2" outward movement for the inner ribs. Then I reset the height so all were level on top. I discovered that non-parallelism made the slides "sticky" at the far end of the shutters.

Careful examination on top showed that the inner slides were being pulled, or pushed, inwards or outwards at only one end. I replaced the original [roofing] battens with 2x4s to have more meat to screw into. Then I had to trim back the ribs up at the top to clear the zenith board. Then all the screws had to be replaced because the originals would not run through the slides without the oversized heads hitting them.

Eventually the shutters could be closed, or opened effortlessly, from anywhere along their length. A frustrating but still interesting exercise involving endless ladder climbing. In retrospect I could have left the ribs untrimmed but thought I had no choice at the time. When I first fitted them the ribs were stretched tightly between the slides. With no way to free them except to trim them back on the inside.

Click on any image for an enlargement.

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