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What finer way could a blazing hot sunny day be spent than barrowing and shovelling a tonne of concrete? ????

This Sunday I started the day by cutting some of the outer floor timbers to length and digging the previously-mentioned radiator brackets out of my pile of scrap metal to use to fix the timbers to the pads. Then came the hard part: shovelling the ingredients for the concrete into the mixer, wheelbarrowing it to the right place and shovelling it out again. I certainly won’t complain about the weather because it’s such a pleasure to be able to spend so much time outdoors, but by the time I finished my clothes were totally sodden with sweat and I was almost on my knees.

Very pleased to have got it all done though. Here’s how it looks now:

Not entirely sure where I go from here. I think I need to get all the concrete work done, but that means knowing exactly how my piers are going to work out so I can sink the bolts into the concrete in the correct places. I might have to finish the pier design and then talk to the chap who is going to make them.

Having decided that I can wrap the timber in DPC material to protect it from damp, this Saturday afternoon I lowered the shuttering for the two concrete blocks that I’d already put in place so that the highest one will have its top at ground level. After that I dug out the space for the two other corners, which didn’t require a huge amount of digging as I found rock about four inches down. In fact there’s so much rock close to the surface that I gave up trying to get the pads square with each other. As long as they’re bigger than the obsy base, that will have to do. The shuttering for the lowest pad still looks huge as the ground level there is over two feet lower than at the highest one. I may well re-use that shuttering for making the pier foundations.

The plan for tomorrow is to get the outer timbers of the floor made up and then get the concrete poured for these four pads. The floor timbers will allow me to place the strapping (which may actually turn out to be some old radiator wall brackets) to tie the frame down accurately.

I have some stones and broken up concrete blocks that I’ll also throw into the pads as I need to get rid of them and it will reduce the amount of concrete I need to make. I do need to be careful that the shuttering doesn’t “float off” given the weight of the concrete though. I might have to rest a few more blocks on top just to stabilise things.

Though I’m not 100% confident in my welding skills, I’m coming round to the idea of making the frame for the rolling roof section from a square section steel tube. I think in the end it will be lighter, less flexible and require a less complex design. It should also mean that I can have a ridged roof rather than a flat roof which I find more aesthetically pleasing. I’ve roughed something out in Sketchup, though it may change.

For holding the roof closed (so it won’t lift off) I’m tempted to use something like this:

which is actually a pin used to mount tractor implements on a three-point linkage. It could pass through a plate with a hole fixed to the walls so the roof won’t lift. When it is to be closed up for an extended period I could even use the usual spring-loaded retaining pin through the hole in the end:

Plenty more to think about before I get that far though.

Once I’d mowed the grass in the planned area I wasn’t entirely happy about the steepness of the slope. The floor deck will be built off six concrete pads and the pad at the bottom of the slope would have been over 600mm high. To reduce the height a little I decided to move everything about another metre away from the house.

That done, this afternoon I started digging out the space for the first two pads. Having the right tool for the job should save a lot of time.

Sadly I was a little slowed down because I managed to jump one of the tracks off the digger. I knew I needed to check it but I forgot and paid the price. Fortunately it wasn’t too hard to lever back on with a long steel bar whilst holding that side of the digger in the air with the bucket and running the track forward (not recommended practice, I imagine, but probably happens far more often than anyone will admit to.

I got the shuttering in for the first pad late this afternoon, recycling the base of a trailer in the process, though I have to admit I’m not entirely sure how reliable the ply is any more. It may not look it, but the spirit level does actually say it’s level in both directions.

I managed to get the shuttering in for the pad on the left (also recycled, this time from a shelving unit that has seen better days) as it was getting dark. Need to check the levels again in proper daylight.

I’d really like these two pads to be a bit lower, but the top of the one in the photo above is only 150mm above ground level and I’m not sure I want to go closer to the ground than that with the timber. Perhaps 100mm clearance would be sufficient. I shall ponder on it before I start the next one.

I’ve been tinkering with Sketchup (version 8 — the latest one I can get to work under Wine) to create a design for the observatory. It’s quite a handy tool for setting things out to see how they’ll all work together, even if it is a bit of a pain to have to create objects for all the different size components.

Initially I just wanted to get some ideas for how the framework and floor would be laid out and whether I could actually fit three piers in, so this is what I came up with:

I’ve placed the external door in the cold side as it means there’s only open door required into the warm room. This should make it easier to keep warm and makes more space available for storage as I don’t have to give up two walls to put doors in.

I’ve since refined that to give a little more height to the warm room and create the slope for the fixed roof.

I’m not 100% sure what’s going to happen with the roof yet. I’ll sort that out as things move forward.

I’ve been promising myself that I’d build an observatory for years, but life has just got in the way a bit and I never managed to get started. I’ve now decided that I should really get on with it, so ordered some of the materials with the view that if I had the stuff here then I could work on it as time was available.

My plan was always to build in the “upstairs field” (a name given unintentionally by my son to the field at the top of the slope in front of the house) but at the moment there’s no easy way to get power there. That may still happen in the future, but for the time being I had to look elsewhere, which has not actually been too easy as very little (almost none) of the ground around our house is level and some of what is level merely acts as a collecting point for run-off water when it rains heavily.

My chosen site is this, which is next to “The Beer Shack” (which already has a power supply that can be used for the obsy). The closest four stakes represent the corners of the actual building with the last one where the roof will roll off to. It’s flatter where the cement mixer is, but there was about 100mm of standing water there for much of last winter 🙁

The size of the observatory will be 4.8m x 2.4m including a 2.4m x 1.2m warm room at the far (north east) end. I intend to have multiple piers to allow a permanent white light/Ha solar rig to be set up on one with night-time kit on another. I don’t yet know how tall my piers are going to be so I don’t know how high the walls will be which in turn means I’m not sure where the door is going to end up. Once I have the floor deck built and can check sight lines I’ll make those decisions.

This gives a better idea of the slope. I’m not entirely sure how the corner of the stone wall appears to be vertical, but the shed on the top right looks to be leaning quite significantly (which it doesn’t). Local gravitational anomaly, perhaps.

And from the warm room (north easterly) end:

The other major compromise with building here is the view to the south west. Or more specifically, how some damn fool built my house in the way without considering that several hundred years later I might want a better view.

The view to the south east is similarly obstructed, but by a mature ash tree. However, I went out the other night and could clearly see Jupiter over the roof of the house so I don’t think it will be too bad. The ash tree is probably on borrowed time too, though I’d not remove it just because it was an obstacle to astronomy.