David's Astronomy Pages Observatory Design & Construction Observatory   Home Page   Telescope

Design Philosophy Design Review Location Pier / Pier to Wedge Mount Preparing the Site  Installing the Pier Building Roll Off Roof Installing the Telescope Cost Lessons & Experience Relocating the Observatory (2001 & 2004)  Roof Changes (June 2005)

Design Philosophy

I've owned an 8" LX200 telescope for 3 years up to 1998, and used somewhat irregularly for viewing various planetary, stellar and deep-sky objects.  The task of setting up the tripod and telescope, aligning it each session was found to be an unwelcome chore. 

In order to make my visual observing more frequent/more pleasurable and in anticipation of the day when I might get an ST-7 CCD imager which would benefit from a permanent setup, I built myself a roll-off roof observatory in my rear garden in which to permanently mount my LX200. Details of the design and construction of the observatory and the permanent pier are given below. 

Because of the high likelihood that I will need to move with my job in the future, the observatory and pier were designed that they can be removed and taken to a new site should the need arise. This feature of the design was tested during the course of 2000/2001 when I moved to southern England. The observatory was successfully dismantled and then, after some time in storage, reassembled at a new site in Dorset (see Kingcup Observatory).   The observatory was again dismantled and moved in 2003/2004 to a new site back in Scotland (see Clair Observatory)

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Design Review

For anybody thinking about building an observatory themselves I thoroughly recommend looking round on the internet to get an overview of the various designs, experiences and lessons of others. For me it provided ideas, inspiration and confidence to embark on the project and complete it within about 6-7 weeks.

Useful sites/documents that I found were

• Chuck Faranda's Hill Observatory
• Scott M Baker's Baker Observatory 
• Frank Loch's Deep Space Observatory
• Don Dillinger's Garden Shed Observatory
• Adrian Catteral's Observatories
• Rob West's Observatory
• Doc G's Info Site & Observatory
• Dick Green's Notes on Two Plat Pier Adaptor for the Meade SuperWedge
• Pier Design and Construction

A source of information that I've since found out is the ATM Observatory Plans Page
(Note : the above external links will open in a separate window)

Besides reading web articles I also contacted a number of amateur astronomers by e-mail and asked for their experiences and suggestions - I was surprised by the quick response, less than 36 hours in each case. Thanks guys.

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Location

The first task was to select the best location for the Observatory. I was limited to using my back garden which lies in a village in NE Scotland. After a little consideration the best spot appeared to be on the site of our existing garden shed, which offered the most reasonable view of the sky (south, west and north), was fairly close to the house and was shielded from direct light pollution, (provided I shifted the existing garden shed over by 2 metres into a position blocking the worst offending street lamp light).  

The village suffers a moderate, but not overwhelming amount of light pollution. Light Pollution is worst when clouds are about, but I normally observe when skies are completely clear.

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Pier / Pier to Wedge Mount

A locally based Engineering Firm (Sun Engineering, Aberdeen) made up the Pier from the designs I provided. The pier was 7" OD in diameter and 3' 8" tall.  The top and bottom plates were 1/2" in thickness and had holes drilled to later bolt the pier to the ground and to bolt on the Pier to Wedge Mount. A 3" ID hole was drilled in the upper plate that would allow sand to be late poured into the pier tube for vibration dampening purposes. The plates were welded to the tube and then four 2" tall triangular fins were welded between the pier tube and the bottom plate for additional stability, whilst three 2" tall triangular fins were welded between the pier tube and the top plate. 

Engineering Drawing (larger view)

A further 1/2" thick circular plate was made for the Pier to Wedge Mount.  3 bolts were welded to the lower surface that would allow fitting to the top plate of the pier and levelling of the Pier to Wedge Mount. A central bolt and 3 surrounding bolts were fitted to the upper surface that would later accept the Meade Equatorial Wedge. A device was also installed to the upper surface that would allow screw directed force to be exerted on the lug on the wedge that would rotate it left or right for alignment purposes.

Engineering Drawing (larger view)

The Engineering firm also made a bolt-cage that would be set in a concrete base to take the pier.  

Initially coated in Red Oxide paint, the Pier was painted Black upon arrival and prior to installation.

The total cost of the Pier, Pier to Wedge Mount and bolt-cage was £280

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Preparing the Site

An existing shed stood on the site and was first moved to an adjacent position. The site was then levelled down to a new deeper level, using spade, wooden posts and spirit level.

Preparing the site

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Installing the Pier

Once the site was cleared and leveled, the location for the hole for the pier base was marked out. The hole was dug out in the shape somewhat like an chemistry flask, with a wide flat base and a narrower neck.  The hole was 30" deep, 30" diameter at the bottom and 20" diameter at the top. Whilst the upper section was known to be made-ground an unexpected surprise was finding a complete concrete breeze block, which had to be removed. The base of the hole was a damp clay subsoil formed from the underlying boulder clay deposits we have here.

Once dug the bolt-cage for the pier was hung in the hole from a temporary cradle made out from two lengths of 1.1/2" x 1/2" batten supported on surveyed and levelled marking posts. The position of the bolt cage was carefully checked and adjusted by 1) checking that the centre of bolt-cage was at the surveyed center position of the observatory site, 2) checking that the compass bearing of the bolt-cage cradle against the compass bearing of a orientation of a set of known pier align points defined on a previous evening.  3) cross-checking that bolt-cage cradle was parallel to those same known pier align points 4) checking that the bolt-cage cradle was vertical 

The pier align points were defined by setting up the pier, wedge and telescope at nighttime on the flat paved area adjacent to the observatory site  and then performing a polar alignment by carefully rotating the pier (note the Wedge was positioned in the centre of its range of Pier to Wedge adjustment at this stage). With this done the positions of the screw holes on the base of the Pier was marked on the underling paving stones.  

The hole was then filled with concrete ballast (a total of around 375 kg), which was mixed directly adjacent to the site. Checks were made on the position and orientation of the bolt-cage through the operation. After letting it stand for a while the Cradle support was temporarily removed and a circular dam placed around the top of  the bolt-cage,which was then filled with more concrete and smoothed off as best as possible. The cradle battens were then replaced and the concrete left to set overnight. 

Whilst the attempt to smooth off the top of the concrete was ok at a first pass, it was clear that it wound not provide a flat stable base for the pier and consequently the top of the concrete was finished off with a layer of floor levelling compound. Once not of great strength (too much humidity & water around ?), it did produce the required level base.

The site was then finished over with gravel and sand up to the level of the tops of previous levelled wooden survey posts. A small amount of work was required to strengthen the downdip end of the site, between it and the newly repositioned older shed.  Concrete garden slabs were then laid on the sand/gravel base. 

Total cost for the Pier Base and Flagstones was £53

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Building

I initially started with idea of having a building structure of 7' by 7'. But I eventually pruned this back to 6' 6" x 6' 6" after setting up my LX200 in our living room and surrounding it with chairs to define the minimum comfortable space needed. I decided that a custom-made pent (sloping) roof garden shed with a door, but no windows would be the best design. Having chosen a height of 3' 4" as the height needed between Floor and Base of Wedge I decided upon a shed height of 5'6" at the front (which would face south) and 6'2" at the rear (which would face north). The floor of 3/4" plywood was specified to have a 12" square hole cut exactly in the centre, allowing it to fit over the Pier (largest diameter 11"). Fixed to 2.1/2" x 3" battens and resting on three  6" x 2" wooden battens, the floor of the shed rests 5" off the ground. In order to make roof as light as possible for rolling off I decided that I would make roof from corrugated bitumen sheets (Caroline) rather than take a standard wooden roof + felt and agreed with the Shed maker (G.C. Carle & Son, Parkhill, Dyce, Aberdeen) that he would provide the Roof Framework only. Total cost including basic lock, delivery and erection was £407.

The shed frame was made with rough sawn wood, and a day was spent sanding down the inside of shed and giving it a coat of Timber-Care. Experience during the first 2 weeks showed that some water was entering the shed along the base of one wall, during conditions of rain combined with strong wind. The shed maker gave me 4 extra boards, which I retrofitted around the bottom of each wall and seems to have cured the problem.

An additional problem that required some attention was the plywood floor which was initially weak along the join between the two sections from which it was constructed. Retrofitting a length of 4"x2" wood beneath the flooring along the line of the join strengthened the floor considerably.

The floor of the shed has been covered by a vinyl floor covering, the hole in the floor around the pier has been filled by a removable 2 part cover and additional locks / security have been added.

The shed does not as yet have its own electrical power outlet, but this is an option for the future.

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Roll-Off Roof

In order to make roof as light as possible for rolling off I decided that I would make roof from corrugated bitumen sheets (Caroline) rather than take a standard wooden roof + felt and agreed with the Shed maker that he would provide the Roof Framework only.

(As it turned out the roof is pretty heavy in any case - corrugated bitumen turns out to be pretty heavy - and requires 2 people to lift it into position, however roll-off operation is pretty easy and can easily be managed by one person).

Corrugated Bitumen sheets were trimmed where necessary and nailed to the roof framework using the Caroline system of nails & plastic bungs. The wooden surrounds were then  fitted around. and Caroline system white poly-foam fitted in the eves.

Meanwhile lengths of right-angled aluminum were cut and screwed to the top of the left and right hand walls of the shed, and wooden stops fitted to top of the front and rear walls of the shed. The former of course needed to be narrower than the width of the roof in order to allow wheels of the roof to 'pass through the front face of the shed.

Castor wheels where fitted to the base of the roof, by drilling tight fitting holes and firmly gluing the castor 'pins' into position. It was original thought that 4 wheels on each side would be sufficient, but it was soon realised that more would be needed and in the end 8 wheels were fitted on each side. Wooden stops were fitted to the back of the roof so that it wouldn't easily roll all the way off and locking devices were fitted to the outside front face of the shed and the inside rear wall of the shed. 

After a few teething problems which required final adjustments the roof now operates pretty well. I worry that it will get stuck when I'm tying to roll-it back after a late night of observing, but it hasn't happened yet ("fingers crossed")
[Note : After a couple of shed relocations, the design started to failed in 2004-2005 whereby some of the wheels would loosen and twist causing the roof to jam when shutting. Remedial fix was employed involving moving the wheels from the sides of roof to new positions on the tops of the observatory sidewalls  [ see Roof Changes (June 2005) ].

Seals and additional wooden battens were on the inside side of the left and right hand walls of the shed were successfully used to make the Observatory pretty weather tight.  

After fitting the roll-off locking devices, but before I got round to fitting proper locking devices for the roof disaster stuck ! The tail end of the Hurricane Mitch (which had produced so much devastation in Central America) then came across to Scotland and produced strong violent gales in our area on the afternoon of 1998-Nov-09. The weight of the roof was insufficient to stop the wind from sucking up and lifting the front edge of the roof. The full force of the wind then got under the roof and flipped it over over the garden fence into a neighbors garden. It was luckily still in tact when retrieved and the damage was repairable. Since then latches have been fitted inside the shed which secure the roof down, yet are simple to unlatch and latch again when needing to operate the roof.

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Installing the Telescope

With all the careful design and construction completed successfully, installing the telescope was a fairly simple matter of screwing on the wedge to the pier, lifting on and screwing down the LX200 and then waiting for the next clear night to perform polar alignment.

First light with the telescope in its new observatory housing was on 1998-Oct-23.

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Cost

Total cost for the Observatory came to £ 910 (pretty close to my budget estimate of £ 900). A breakdown of the costs is as follows :

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Lessons and Experience

• Look around on the Internet for design ideas and experience, contact a few people through email and ask for advice 
  (I found this to be a highly valuable step)
• Make sure you build in and use roof locks on any sliding roof shed
  (I lost the roof twice, once before fitting locks and once when I forgot to use them)
• Make the roof as light as you can  
  (my roof is just manageable, but I would prefer it to be a lot lighter)
• Consider how the design will effect your viewing of low altitude objects
  (whilst Mars was visible from my site for 2001 opposition, the wall of observatory prevented me seeing the planet with the telescope, a dome design may be better for you)
• Construct spare (pier base) bolt cages right at the beginning
  (when I moved my relocatable observatory, I then found that I needed to find a company/welder to build one (I got two) in my new town/village)

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Relocating the Observatory (2001 & 2004)

The observatory and pier were designed so that can be removed and taken to a new site when the need arose. This feature of the design was tested during the course of 2000/2001 when I moved to southern England and again in 2003/2004 when I return to a new site back in Scotland.

The construction plan that was used  for re-erecting the observatory at the Kingcup site is listed below.

The construction plan that was used  for re-erecting the shed observatory at the Clair site is shown below

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Roof Changes (June 2005)

The roll-off roof was originally constructed with sets of wheels along each side of the roof. These ran along rails mounted on the top of each sidewall of the observatory and allowed the roof to be rolled-off/on.   Whilst the design originally worked well, there were increasing problems with it during 2004-2005, whereby some wheels would occasionally loosen and twist, causing the roof to jam when shutting (not the most desirable event when you're tired and cold).  

In June 2005 remedial work was carried out to relocate the wheels into positions on the top of each sidewall, thus allowing the roof to easily roll off/on, using the sides of the roof as rails.

Old Wheel/Rail Design
New Wheel/Rail Design

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