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Claines Top Observatory - construction

Pier
Cross section of pier hole.


Absolutely essential to good hole digging is to prepare the hole to start with. Place shuttering round the top in the form of a wooden frame. This will allow the surface to be levelled with respect to the foundations. Wrap the wood in plastic sheeting as wood and concrete don't get along too well - it also enables the shuttering to be removed easily afterwards.


Tamp down the base of the hole with lots of stone or rock. We used smashed up paving slabs hammered down with a sledgehammer ( see picture below ).

This all went according to plan until we reached the base of the hole and nearly fell through the roof of a WW2 anderson shelter! Luckily it was mostly filled in and only the side of our hole caved in - the last thing you want to find when digging a hole is another one !

The pier itself is a 5' long aluminium tube. An attachment at the end has been turned by Chris Livingstone , Worcester's premier telescope maker and all round good guy ( with a huge lathe in his garage ) , to enable my gp-dx mount to be screwed to the top of the pier.

Here is the exposed metal roofing beam and wooden walls of the shelter alongside the extra tamping we had to hammer into the ground.


Alignment

Once the hole was shuttered and the rock base present it was time to put in place and align the pier itself. Ensuring that with the mount screwed into place the pier itself was vertical and pointing towards the pole star, it was tethered in place and lots of concrete was mixed ( by hand ) & put in the hole. 16 bags of 25k concrete were used in total. The concrete mix was supplemented by aggregrate of more smashed up paving slabs. {NOTE} I was planning to use a tube of sonotubing 18" wide to surround the pier in the base to provide extra vibration dampening. However, no matter how well the cardboard tubing is protected it will still rot in time, leaving a smaller less stable base, so I decided against this.



2 pictures of the pier set with guide wires, and the next day.


Power

Armoured garden pump 3 core mains cable was laid from the house in 32mm piping underneath the patio & garden path where neccessary, buried between 3" to 12" depth depending on whether it was underneath a paving slab or not.


Shed


The shed is a standard Yardmaster 8' by 6' shed made from galvanised steel, held together by hundreds of little self-tapping screws. The corners of the shed are anchored down in each corner to a cubic foot of cement.


Frame


The frame was constructed at the same time as the shed was assembled and is made from 3' by 3' sawn wood primarily to enable the roof to roll on & off with ease. As it turns out the wood seriously strengthens the structure itself, which could twist & warp quite easily on its own. As the panels were bolted on, the 3' by 3' beams were continually unscrewed and re-adjusted to fit the shape of the shed, which started insecurely with plenty of slack . When all the panels were in place, the frame had become absolutely rigid. The key was to not to secure the remote supports until the main frame surrounding the shed had been finalised. This was also definately a 2 person job , not just to help hold & fit beams together, but also to decipher the instructions, which kept referring to the wrong parts for each section :-\ - so thanks Sarah ! xxx

The shed is also bolted directly onto the wooden frame as well as the metal skeleton, providing further support and security. 3/4 mitre joints at each end provides stability & support for the main beams, each 4.8m long.

This structure was structurally tested by 60-70mph gusts of wind without any damage thanks to the cranky british weather ( around 20/10/04 ) , which is just about as bad as it can get , so it is safe to say it is solidly built ! I would not have put money on it surviving without the wooden frame however.


Roof


The roof is built on a 1" by 3" frame with nylon wheels bought from screwfix direct. The main runners have 15mm wooden beading nailed to the side to keep the roof on its track. The roof is secured with carriage bolts driven through both the roof & the main frame , connected via steel bars with holes drilled into them.As well as the shed having standard security functionality I have added some extra security features which help prevent unauthorised entrance.


The roof is secured down with many turnbuckles which securely self-clamp the roof in place.


For the protective finish Cuprinol Willow is pretty much an exact match to the shed colour.


Inside


All joints and connections on the inside are sealed with translucent bathroom sealant to keep bugs out and water coming in round the base. As the shed is built directly on paving slabs , rain falls down and dissipates through the cracks instead of pooling on a flat concrete base ( which was another option on which to build ). There is a sufficient airgap around the roof to keep fresh air flowing through the observatory to reduce condensation. Cement has been used to level the floor internally , leaving a gap between the pier & the floor to stop any vibrations. Expanding polystyrene gapfill has been used where neccessary.
On top of the floor is a waterproof membrane and on top of that is an artifical floor constructed of 2" by 2" wood topped with 18mm ply and carpet tiles.


The walls have 25mm polystyrene sheets underneath 6mm marine ply.



Completed Interior




Cost

Total cost of parts , including shed, wood, concrete/cement,pier, screws, nuts, bolts , flooring and wood, was around 700.


Workforce

None of this work could possibly have kicked off without help from friends & family , and special thanks go to 2 good friends who just conveniently happen to be Royal Engineers on leave, without whom in all probability this all would look like the tower of pisa. Invaluable hole filling (almost as fast as we were digging it ) also came from my two sons , overseeing the dig here.Loads of thanks to Toff, H, Rory, Harry & of course Sarah.