Hilltop Observatory

[Jokehoba]

Last summer I decided that I wanted to build an observatory. Initially I planned to extend the patio which would give me a view of the NCP and act as a platform to set up the telescope, etc. Then, in time, I would build a roll-off roof observatory on this foundation. I started to dig footings but then, heeding the advice of the importance of getting the location right, I put everything on hold and decided to rethink my plans.

I'm glad I did, and have changed my plans to a dome, based on the Sky at Night build by Mark Parrish, published in 2009. It will be about 3m diameter and as you can see, it will dominate the garden. I plan to make it possible to dismantle, should I move. Future owners can turn it into decked area or gazebo or something!

I confess I started the observatory build in April and so am a bit late in starting this topic. In any case, progress had been slow for various reasons, but things have moved on with the good weather over the last few weeks.

For now, here are the initial pictures from April but I will bring things up to date very soon.

John

[nameunknown]

Hey! big hole is a great start.

looking forward to the rest!

P

[lguise]

Looking forward to watching your build. Just have a care about the overall height if it's a 3m dome on walls you may get over the limit before planning permission required and you have neighbours near. Max height seems to vary in different regions but where I am it is 3m.

Good luck with the project and keep the pictures coming!

[Jokehoba]

Just have a care about the overall height if it's a 3m dome on walls you may get over the limit before planning permission required and you have neighbours near. Max height seems to vary in different regions but where I am it is 3m.

Yes I was concerned about this and indeed did contact the local planning office before I started digging. Around here the maximum height is 4m. My worry was how they would interpret a domed roof as the guidelines only specify flat or pitched roofs. Thankfully I was told it was within the limits allowed.

John

[Jokehoba]

With the digging all done by the middle of April, I decided to start filling the eight outside pads. Idiot that I am, I decided to mix the concrete by hand! It took about two weekends just to do the pads. Common sense prevailed as I contemplated the central hole - about 3 times the volume of the eight pads put together!  I would borrow a concrete mixer...which I didn't manage to get hold of until the middle of May.

So here are some pictures of the main concreting phase. The garden slopes substantially so the pads towards the back are quite high (and required even more concrete). I intended to construct a concrete pillar, hence the rebar. So much easier with a concrete mixer...

John

[Jokehoba]

So, after completing the concreting of the central block I lowered the tube I was going to use as the pier over the rebar...only to find I'd incorrectly measured it's internal diameter! All my measurements had been based on a short length of pipe (160mm across) but it turned out the full length pipe was only 140mm across. 

After halting everything for a week to consider my options, I decided to make my own octagonal shuttering from plywood rather buy 160mm or 200mm sewage pipe. The next series of photos show before, during and after for the pier construction. 

With hindsight I should have braced the central section as well - 3mm ply doesn't hold up too well against wet concrete. Still, duct tape came to the rescue. I also made a better job of tamping the concrete as I got to the top of the tube than at first. Thankfully most of that will be below floor level.

John

[mhard26339]

Looking good John, hindsight is wonderful but I have had problems with wayward shuttering when pouring concrete before so I used 18mm MDF this time, secure but a but pricey. I still managed to set my pier 15 degrees out so had to (well Tinker 1947 had to) re-drill my holes on the base plate, still all in and polar aligned now. I guess all of the metal about pulled the settings on the compass?? again hindsight.

Regards

Mike

[Soupy]

I used chipboard flooring for my boxing in John and I had problems with the concrete trying to break out as well... If anyone is considering doing hand made concrete bases to piers make sure to properly brace the joints...

[Jokehoba]

Last weekend was great weather and allowed me to crack on with construction. I finished cutting the wood for the main framework and screwed and bolted them together. First, I placed the posts on their respective concrete pads to get an idea how big it was going to be. I bet the neighbours thought it strange to be erecting my own wooden Stonehenge on the day of the Summer Solstice!

After loosely screwing in the cross-members, it proved quite time consuming getting the structure centred. I began to wonder if I had got my measurements wrong as some posts were way off the centre of their pad. 

Anyway, after screwing everything together and packing up for the day, I got inspected by a local resident...

John 

[nightfisher]

Nice design, and the project is coming along nicely now

[spaceboy]

Is this obsy for visual or imaging astronomy John ??

[Tinker1947]

Your local Owl will love the perch while looking for mice ect, the build is looking good........

[Jokehoba]

Is this obsy for visual or imaging astronomy John ??

This is going to be primarily for imaging. The time and effort it took to assemble all the kit, align it all and then dismantle it at the end of the session was getting a real bind. So much so, there have been nights when I decided to watch TV rather than go out.

I may yet build a small platform next to the patio so that I can still set up a small scope for visual use. Last month I decided to simply observe some globular clusters, rather than image them. Must say they sparkled more beautifully in the eyepiece than on the PC!

[Jokehoba]

This entry brings the project up-to-date. I managed to do a little more almost every evening last week but rain yesterday meant I could only add a small concrete pad for the step support. Talking of which, I discovered a lump of old concrete and brick which seemed to stretch from the step pad to the main mount block. I was concerned it was touching the main block and would introduce small vibrations especially when using the step. I managed to break it up with an SDS drill. Would have so much easier if I'd noticed it before all the construction!

Today I completed the floor joists and step support. Next I will attach the feather edge boards.

Pictures show the first joists around the pier; the unexpected concrete removal; and the completed joist work, with a close-up of the step.

I am pondering whether to do a slightly different dome design to the Sky at Night plan... Perhaps cut more but smaller hardboard panels for a smoother dome? Or go for a geodesic structure? Or a simple turret like http://www.progressiveastroimaging.com/davesastronomy/index.html. Any thoughts from people who have built their own dome?

John

[Tinker1947]

Nice work, are you covering the frame with a breathable membrane before the feather board goes on..???

[Jokehoba]

Nice work, are you covering the frame with a breathable membrane before the feather board goes on..???. 

Thanks for the encouragement. I hadn't thought about a breathable membrane - it's not mentioned in the original SaN plans. But I agree it's a good idea so I'll go get some. Cheers.

John

[Tinker1947]

Holding the membrane in place, i found a staple gun with stainless steel staples made it a quick and easy job.....

http://www.wickes.co.uk/Heavy-Duty-Staple-Gun/p/168658?CAWELAID=120135120000007236&CAGPSPN=pla&utm_source=google&utm_medium=cpc&utm_term=&utm_campaign=Product+Listing+Ads&tmcampid=104&tmad=c&tmplaceref=&tmcustom=mkwid|W5fPyZGt_dc|pcrid|7531858372|&gclid=CjkKEQjwlcSdBRD3wva3-KOAo80BEiQAjNIhidCM90sHwH5P6GZ8X36zjFKdWzmywB76dSF3sjp3AaDw_wcB

[Jokehoba]

Well I pressed on yesterday, cutting and screwing all the cladding in place...before reading Tinker1947's suggestion of attaching a breathable membrane! After a quick visit to Screwfix, I tried retro-fitting the membrane from the inside. Not a very neat job. So to do it properly, I removed all the panels, stapled in the membrane (thanks again Tinker1947), and reattached them. 

[Grotemobile]

Its all looking very good.Wait till you

get the dome on.I bet your pleased,

with how things are going so far.

Steve

[lguise]

Cracking job so far, I think it was well worth going back and doing a proper job with the membrane. Looking forward to seeing the dome take shape.

[Jokehoba]

Its all looking very good.Wait till you

get the dome on.I bet your pleased,

with how things are going so far.

Steve

Thanks Steve.  Yes, I am pleased at how it's going and itching to get it completed - now the nights are drawing in! 

[Jokehoba]

I've started cutting out the plywood arcs that make up the wall ring. According to the SaN plans the radius for the wall ring and dome ring sections are the same. I've only cut out a few but I'm thinking that this leaves no clearance to rotate the dome! Surely the dome ring has to be bigger than the wall ring?

Also, I laid a couple of sections on the wall posts to get an idea of fit. While they covered the posts OK, they were not getting any support from the top of wall beams. It's only 12mm ply, which would bow under the weight of the dome.

Looking at the construction photos from SaN, the wall ring is clearly supported by the wall beams, while the plans show only support at the posts. I think I will adjust the wall ring diameter so that it is fully supported but still covers the posts. Glad I realised this now - it would have been a real pain to have trim them or cut new ones. 

Another observation, the top of my wall doesn't form a regular octagon. Post-to-post diameter varies at worst by a couple of inches. I can accommodate this by ensuring the wall ring covers the posts. Or maybe I can tweak it into shape when I attach the ring... Perhaps attaching the wall ring before I fixed the main frame would have ensured a perfect octagon? Oh well, next time...

John

[Teslar]

Fascinating to see this build John. I contemplated it for a while before I saw the opportunity to buy a 3M dome and went that route

[Stridor]

I love following these DIY builds; yours looks really good.............it will, and no doubt does already, give you an immense amount of satisfaction having designed and built it yourself................well done.   

[Jokehoba]

A little more progress... and by the way, thanks for all the positive comments.

I've cut and fixed the wall ring, having adjusted the measurements to make it about 10" wide rather than only about 6", as per the original plans. To ensure a perfect circle, after cutting all sections with a jigsaw, I attached a central block to the main pier, to the height of the wall. Then I made a jig and attached the router to it and smoothed out the curves.

I've cut all the dome ring sections (though they still need the ends trimming) and will start putting it together in the area between the observatory and the patio. The gap is just over 3m and it will be tight! I'll sit the ring on blocks but somehow have got to make it level.

John