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Wednesday 29th June. Getting the [replacement] ladder into place was a real struggle. I had added a lot of 2x4 braces to the lower octagon walls. So in the end I had to push the ladder up onto the obs. level and then lower the ladder [very carefully] down the hole in the middle. Not an easy task for something 12 feet long and weighing nearly 40lbs. Thanks to the ladder's slightly more westward position I have now more headroom as I climb.
I went around adding plates to reinforce the miters on the veranda perimeter joists. The image below shows a nailing plate and a joist hanger. I am using specialist Torx screws designed for firmly fixing these steel parts. The shanks of these self tapping screws are a close fit in the drilled holes to maximize the strength and powers of location. I have almost run out of screws so will have to buy more to finish the job properly. I also screwed the footing brackets to the support posts with 3" Torx screws.
The entire building is very stiff in line with the main beams but not at right angles. If I push hard across the building N-S I can get it swaying by about an inch at 2-3Hz. The plywood cladding should stiffen up the building and kill this tendency to sway. It is amusing to watch the pyramidal pier remaining rock solid as the entire building moves around it. Though it often looks as if the pier is moving instead, it is very resistant to any movement. The cost of all those cladding sheets is a worry. I need eight full sheets for the lower walls. If I have to use 8 more full sheets on the upper obs. walls, as well, then 16x anything adds up to a lot of money!It now occurs to me that I have a perforated steel strip for stiffening roofs against lozenging. I could try to stiffen the building with this stuff. Since it takes up virtually no room compared with a diagonal timber brace. I was looking at the building yesterday and there are no clear runs for large, timber braces.
Cladding the top of the pyramidal pier will help to further stiffen it. I have been trying to imagine a suitable space for the drive electronics within the upper pier for weather protection. The plan is to clad the top section with ply first and only then to trim back the slanting tops of the 4x4 posts. That should ensure they all end up perfectly flat for the mounting base plate to rest on. I may add a plywood sandwich first for a more secure fixing.
A sturdy central [threaded] stud will hold the mounting down and allow fine rotation in azimuth for alignment. It is completely impossible to rotate the pyramidal pier itself as it is bolted to concrete footings.
Thursday 29th: The threat of rain limited my options so I attached a 1x6 larch skirting board to the bottom of the nearby shed. Heavy rain stopped play just as soon as the job was competed. The idea is simply to keep any rodents out. A task previously left to a row of old house bricks and heaped gravel for decoration. The gravel was a useful indicator of excavation but was never visibly disturbed. A sprinkling of the new gravel on top will leave it looking a lot tidier
and less likely to splash mud or sand onto the cladding boards.
Once I have trimmed back the projecting timbers of the obs. building I shall have to add guttering to the shed eaves. If the shed roof [or observatory] rains down into the shady gap it will be very slow to dry. Probably increasing the chance of rot.
The image shows the exposed top of the ladder. The present mixture of loose boards and spare 2x8s is just a temporary working surface. The ladder will eventually be tightly surrounded in larch floorboards. Which is why I added the longer joists to allow close and firm support on either side. It would not only be dangerous to have large openings in the floor but would make transition from ladder to observatory more difficult than necessary.
The ladder is designed to rest against a wall, or other hard surface, at the very top of the handrail extensions. I am resting the ladder firmly against a 2x6 joist at the top tread. This will prevent the ladder top putting too much inner pressure on the obs. cladding plywood. While still retaining enough outward pressure to provide the necessary stiffness in the handrail extensions. I may add a wooden cross brace with holes cut for the rubber end plugs to closely locate them against all lateral movement. You never know when you might need that extra strength when carrying up a large or heavy object and need to step sideways while clinging onto the handrails.
Anybody else building such a 2-storey observatory arrangement should seriously consider putting the top of the ladder and trapdoor on the south side of the pier. Assuming they intended to use a refactor or SCT, of course. I checked and I do have plenty of room for the long refractor focuser to clear the handrail. Most observatory owners would probably not choose to pierce the hatch opening with handrails. Having the ladder just there may eventually get on my nerves. I seem to spend a lot of past observing time enjoying rising planets or the Moon in the eastern sky. Primarily because that was the only clear sky available to me!
For imaging handrails or trapdoors won't matter at all. Because I won't need to stand just there. I could have cut the main beams and heavily boxed in the gap where the ladder would fit but didn't want to weaken the structure. In retrospect I could have had a square beam structure. If I double up the 7" refractor with the 10" f/8 Newtonian then I will probably want to stand to the south of the pier anyway. Compromises are inevitable in such a situation. I shall just have to be very inventive in providing a suitable trapdoor/hatch to avoid accidents or silly tripping points.
I seem to have settled on a hinged design of hatch. Though a sliding one might make more sense. It can be pushed into the pyramid pier when open and then return to its normally closed position covering the top of the ladder. Such a design might avoid open gaps in the floor. A flap, hinged jest beyond the ladder top, would need to be tapered to slip inside the tapering pier framework. A sliding hatch cover could be as wide as the inside measurement of the handrails. That said, the taper portion of the hatch would lie well inside the pyramid when [normally] closed. So any gaps with the floorboard would be well beyond accessible traffic areas.
One slight worry is the density of 1.25"x5" larch floor boards if I used that for a floor matching hatch. Lifting a large hatch [minimum 52x90cm] might involve considerable effort pushing from below. Suggesting the use of a pulley system from the ground floor prior to climbing the ladder. The hatch would be tilted well back from the ladder so there would be no danger of it dropping unexpectedly when open. A counterbalance weight might be appropriate if the system was simple and absolutely foolproof. Then the hatch could be dropped down more safely when up in the observatory.
Unfortunately it is not possible to hinge the hatch to the pier. However convenient that might be, it would instantly short circuit the pier's isolation from the building. Any means of counter-weighting would need to avoid wires or cords running across the floor. So it would need levers going upwards and backwards [@ 45°?] with the weights hanging down under the veranda.
A sturdy central [threaded] stud will hold the mounting down and allow fine rotation in azimuth for alignment. It is completely impossible to rotate the pyramidal pier itself as it is bolted to concrete footings.
Thursday 29th: The threat of rain limited my options so I attached a 1x6 larch skirting board to the bottom of the nearby shed. Heavy rain stopped play just as soon as the job was competed. The idea is simply to keep any rodents out. A task previously left to a row of old house bricks and heaped gravel for decoration. The gravel was a useful indicator of excavation but was never visibly disturbed. A sprinkling of the new gravel on top will leave it looking a lot tidier
and less likely to splash mud or sand onto the cladding boards. Once I have trimmed back the projecting timbers of the obs. building I shall have to add guttering to the shed eaves. If the shed roof [or observatory] rains down into the shady gap it will be very slow to dry. Probably increasing the chance of rot.
The image shows the exposed top of the ladder. The present mixture of loose boards and spare 2x8s is just a temporary working surface. The ladder will eventually be tightly surrounded in larch floorboards. Which is why I added the longer joists to allow close and firm support on either side. It would not only be dangerous to have large openings in the floor but would make transition from ladder to observatory more difficult than necessary.
The ladder is designed to rest against a wall, or other hard surface, at the very top of the handrail extensions. I am resting the ladder firmly against a 2x6 joist at the top tread. This will prevent the ladder top putting too much inner pressure on the obs. cladding plywood. While still retaining enough outward pressure to provide the necessary stiffness in the handrail extensions. I may add a wooden cross brace with holes cut for the rubber end plugs to closely locate them against all lateral movement. You never know when you might need that extra strength when carrying up a large or heavy object and need to step sideways while clinging onto the handrails.
Anybody else building such a 2-storey observatory arrangement should seriously consider putting the top of the ladder and trapdoor on the south side of the pier. Assuming they intended to use a refactor or SCT, of course. I checked and I do have plenty of room for the long refractor focuser to clear the handrail. Most observatory owners would probably not choose to pierce the hatch opening with handrails. Having the ladder just there may eventually get on my nerves. I seem to spend a lot of past observing time enjoying rising planets or the Moon in the eastern sky. Primarily because that was the only clear sky available to me!
For imaging handrails or trapdoors won't matter at all. Because I won't need to stand just there. I could have cut the main beams and heavily boxed in the gap where the ladder would fit but didn't want to weaken the structure. In retrospect I could have had a square beam structure. If I double up the 7" refractor with the 10" f/8 Newtonian then I will probably want to stand to the south of the pier anyway. Compromises are inevitable in such a situation. I shall just have to be very inventive in providing a suitable trapdoor/hatch to avoid accidents or silly tripping points.
I seem to have settled on a hinged design of hatch. Though a sliding one might make more sense. It can be pushed into the pyramid pier when open and then return to its normally closed position covering the top of the ladder. Such a design might avoid open gaps in the floor. A flap, hinged jest beyond the ladder top, would need to be tapered to slip inside the tapering pier framework. A sliding hatch cover could be as wide as the inside measurement of the handrails. That said, the taper portion of the hatch would lie well inside the pyramid when [normally] closed. So any gaps with the floorboard would be well beyond accessible traffic areas.
One slight worry is the density of 1.25"x5" larch floor boards if I used that for a floor matching hatch. Lifting a large hatch [minimum 52x90cm] might involve considerable effort pushing from below. Suggesting the use of a pulley system from the ground floor prior to climbing the ladder. The hatch would be tilted well back from the ladder so there would be no danger of it dropping unexpectedly when open. A counterbalance weight might be appropriate if the system was simple and absolutely foolproof. Then the hatch could be dropped down more safely when up in the observatory.
Unfortunately it is not possible to hinge the hatch to the pier. However convenient that might be, it would instantly short circuit the pier's isolation from the building. Any means of counter-weighting would need to avoid wires or cords running across the floor. So it would need levers going upwards and backwards [@ 45°?] with the weights hanging down under the veranda.
Click on any image for an enlargement.
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