Dome build: Shutters: Scaffolding, slides and shutters.

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Scaffolding:
I spent some time providing 2x4" notched "legs" for the horizontal bracing ladder. This will allow me to stand on the thick plywood laid on top of the ladder. Giving me much better access to the outside of the dome. Standing on the big outside ladder pushes me out too far. So I have to stretch just to touch the dome.

I also fitted the lower slides to the 2x8 across the bottom of the observation slit. Just to get a feel for how the shutters will attach. The support member[s] for the slides will need to be midway between the front and back of the shutter.

Shutter skeletons in place to check clearances. I can't rotate the dome at this point because the shutters are resting on the board on top of the horizontal ladder.

I now plan to add the slides to the shutter doors last. I just need to prop them, from the bracing ladder surface, to take their weight. Then reach inside the shutters from within the dome to put the fixing screws through the extended slides. If I can't reach easily I shall just have to remove the two lower panels from the dome on either side of the slit for easy access.

It's odd how new ideas pop up from making simple changes elsewhere. The braced ladder, now acting as firm scaffolding, opens up new possibilities. I have fitted the U-section of the ladder side rail around the octagon base ring timber with lots of long screws for security. So it can't rise or fall out of position and the big outside ladder is already forcing it inwards. With the screws providing extra security.

Shutter drawer slides:

I took the outer ribs down and fitted the top slides. Then I quickly threw the shutters together. Since they will be plywood clad from existing 4mm sheets I don't really know where to put the crossbars yet.

I was struggling to make any sense of the obstructions at top and bottom after I carried both shutters up bodily, in a gale and plopped them over the dome. I can only assume that the inner  ribs of bi-parting shutters have to be notched to clear the slides. Nothing else makes much sense unless the slides are fitted literally underneath the doors. My slides are about 10" above the present bottoms of the doors but very close to the ends of the ribs at the top. As it stands my doors won't snuggle down against the dome because both sets of slides are literally getting in the way.

I've done an online search for domed observatories and it seems some people make the inner ribs much narrower than mine. I think I'll try notching around the drawer slides first. Though narrower ribs would certainly be lighter they would also be weaker.

It is possible I may have made an error on the radii of the shutter ribs. I cut them to 150cm and 165cm inside and outside radii because I thought they'd sit much lower on the dome. Because the slides are pushing the ribs out more than  expected, this exaggerates the error. If I can get them nearer the dome the problem [largely] goes away.  I could re-cut the inner radius larger to match their final situation. Making new shutter ribs means another £40 equivalent in materials alone and hours of work. I'd rather solve the problem by lowering the shutter ribs closer to the dome.

I had my first experience of the dome in darkness as I covered it over for the forecast, overnight rain. Sadly the sky was clouded over so there were no revelatory moments. The Moon would have been well placed clear above the house. The previous night it had been completely invisible from the garden below. But easily seen from the observatory floor.

The observing slit seemed much narrower after the shutter skeletons went on. The shutter ribs seem to block the sky. While the half width doors seemed strangely narrow with the middle ribs in place. I am used to standing well out of the observing slit to haul the tarpaulins up off the veranda floor at the back of the dome with a rope. This will change when I can open the shutters. Hopefully tomorrow. All this will change again when the big stepladders and their ratchet strap guy-lines have gone. Leaving the dome empty but for the big mounting on its pier. I shall probably go on ducking for months after that even when the ladders have long gone.

Monday: Trimmed notches on the insides of the [central] shutter ribs, top and bottom, to clear the slides.  I do now have the ribs closer to the dome but it's still not optimal. Paused for lunch to think about it. Perhaps making new ribs to longer radii is the answer.

Click on any image for an enlargement.

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