I am building the Observatory for My HEQ5 with a short fast refractor for imaging and my LX90 SCT mainly for viewing, so my pier must allow me to easily swap scopes if necessary.
Design principles and interesting features:
Basic design: Concrete Plinth + Altair Steel Pier + Off-the Peg Shed
Pier: I chose the Altos pier because it looked sturdy and allowed some final leveling and North orientation after installation. It has a variety of fixing options and adapters, plus I might move and could take it with me. https://www.altairastro.com/altair-skyshed-8-observatory-pier.html
Shed: Went for a 10 x 6 shed. Intend to build just a 6×6 roof, which will slide over the other 4 foot bit + 2 foot more. The four foot section will be the warm room with a flat roof. I can build the internal partition after the shed is erected. Wanted a Shed that could be easily adapted and found the “Rowlinson Premier Shiplap Apex Shed 6X10” Price: £514.99 inc delivery This is good quality, but the real bonus is that the apex sections are separate. You build the four walls at level height and then the two apexes go on the ends. This will allow me to then easily adapt the design by attaching rails to the bottom box section and then wheels to the roof bit. The shed sides are also slightly taller than a standard shed at 172cms giving me some welcome headroom. The roof comes in sections, so building just the 6 foot bit looks straight forward (In theory). It is worth shopping around for sheds as the same model can be different prices on different sites.
Wheels and Rail: I think this bit is neat, I am using a wooden slotted fence posts as the rails. Wheels: B&Q TENTE FIXED CASTOR 45MM product code 3700001799978 price £2.14 each rated as 40kg each and I am using 8 of them for a 6 foot roof Rails: B&Q NEVA HALF WOODEN FENCE POST 70X35X1800MM product 3663602942825 £7 each and I am using two on each side for a total length of just under 12 foot. I looked at Aluminium rails but during a wander round B@Q I found these wood posts with grooves in them. I tried the wheels in store and it looks fine. Added advantage that they can also form part of my Obs structure.
Pier base: As per Altair instructions a very large hole in the ground filled with concrete. However my base is a plinth that protrudes 35cm above the base level. I calculated the height needed to elevate the pier so that my tallest mount (The LX90) would just fit under the closing roof. If I had mounted the pier at ground level I would have reduced my min elevation angle to 60 degrees for my shortest scope/mount combination. With the extra height I get down to 25 degrees, less if I raise the pier head. The pier also has a narrow central hole, so I have run a cable in a 12mm pipe through the concrete block and up through the middle of the pier.
Shed Base: Paving stones laid after the pier is installed. I will run a 40mm pipe under the slabs to carry all the other cables to the pier.
The pier base and plinth
I completed the first stage and poured the concrete for the pier base and plinth as per the instructions on the altair web site. The concrete goes 80cm below the ground and 45cm above, with a 10cm base that leaves a 35cm plinth. I used a wooden former to contain the concrete above ground. I made it of 9mm ply with screws every few inches. On top I attached a template holding the fixing bolts which were pressed into the soft concrete. Even so the weight of the concrete nearly burst the mold and I had to reinforce with paving slabs. See picture, but it looks fine now. See pictures)
I should add that I employed a local garden handyman to dig the hole and pour the concrete. The next stage is to lay the slabs for the base.
Added a paving base, It may look a bit wonky in the photo, but its dead flat with a slight incline to allow drainage. Note base is a collection of old slabs I had laying around plus some new ones. Off for a week now and will start on shed building when I get back. Now thinking about electrics, until now I have used a Skywatcher power pack, rated at 7ah to run the mount and a dew heater. I have a Dell XPS laptop which has long battery life, so don’t need to power that. Will probably install LED lights, am I missing something, coffee machine?. Will see how power goes but might upgrade to leisure battery, 100 ah +. Obs is about 30m from house so could run extension cord for recharging. As advised above will also paint underside of shed before installing. Any particular coating good for that and outside? Manufacturer just says “external wood preserver.”
Finally I noted that there is a hole burrowed under the adjoining fence, looks like a fox. Plus I know there are rats around in my rural location. Is this likely to be a problem?