Dave's DiY observatory - Chapter 4

[centroid]

As the observatory backs onto open countryside, and in winter the trees at the back are bare, I was often prevented from imaging when the wind was strong enough to cause the scope to tremor, thus spoiling the images.

The 12" scope with an ED80 on top (now an 80mm APO), presented quite a large target for the wind, and was noticeably worse in this respect, than was the 10".

So, last year I looked at changing from a roll-off-roof, to something that would provide greater protection from the wind.

Some sort of rotating dome arrangement, was the obvious solution.

I looked first at buying a Pulsar Dome and Track, but just couldn't justify spending that sort of money (circa £1800 I think it was), on a small roof for an obsy that cost a fraction of the price.

I next considered building a dome, looked at what was be involved, and decided against it.

I settled on my own design, for an octagonal shaped rotating turret arrangement, with flat roof, roll off hatch, and dropdown door at the front.

Some time was then spent, considering the materials to be used, and making a scale drawing, that I could work to. The turret would be built away from the obsy (in the garage actually), and it would have to fit precisely onto a circular track, if it was rotate.

The turret would be constructed, using a timber framework, clad with T&G cladding, and an exterior ply roof and hatch.

Angle iron was the material chosen for the ring track, and this presented some intial difficulty, in that there aren't that many engineering companys that can 'cold roll' angle iron into a circle, especially without putting ripples in it.

Eventually, I located a small company in Lowestoft that could do this, and that was prepared to do a 'one off' job, at reasonable cost.

On their advice, 5mm gauge angle iron would be used, as they were confident of rolling this into a 1.8m dia ring, without rippling it.

They made a perfect ring, to precisely 1.8m dia, and closed it with a weld, which was ground flat on the running surface. The cost was £100, which included almost £40 for the material. IMO, this was quite reasonable for a 'one off' job.

In order to cut the very large number of joints, and the compound angles involved, I invested in a powered Mitre Saw (well under £100 from Screwfix). This proved an invaluable tool, making every joint and angle so repeatable.

The end result, was a turret, which when fitted with its eight fixed castors, dropped perfectly inplace on the track, and rotated freely with 'sticking' at any point. Phew!!!!, that was a relief .

The angle iron track, was made with its 'toe' pointing inward, and four horizontally mounted fixed castors, were attached, equally spaced, to the base frame of the turret. These run against the upright section of the angle iron track, and keep the turret centered.

The roof hatch had eight small fixed castor attched to the underside of its wooden framework, and these run on 30mmx30mm angle iron track. The track continues beyond the rear of the turret roof, onto a small support framework. Thus, the roof hatch can run completely clear of the roof aperture.

The exterior ply roof and hatch, are coated with several layers of Thomsons High Performance Roof Seal. This is a water-based sealant, that remains flexible when dry. This has been in place since April 2008, and I've had no leaks, or damp patches, and it still looks as good as it did a year ago.

Dave

To be continued:

[wayne bradbury]

Hi , I'm very interested in your observatory design . I wonder if you could help me regarding the size , length and width of your observatory . I know it sounds cheeky but I would like to build a copy of your observatory and any help would be appreciated . many thanks , Wayne  Bradbury .

[m.tweedy]

he has not been on forum since 2009 so unlikely you will get a response

[Robd]

As M.Tweedy says Dave has not been around for a while, if memory serves correctly he has given up the hobby due to ill health.

As it happens we were building our observatories at the same time. Other than the very obvious difference,  can you spot it?, Dave managed to get a metal guide ring where I stuck with wood.  On www.dipplestars.org.uk/Galleries /Observatory you can see the saga of the evolution of our observatory. 

No sizes on there but may be of some use

As a guide the turret circles are nominally 2m diameter. The original fibre glass dome was nearer 3m, and to be honest we miss the extra size.

Height wise it's governed by available horizon, height of mount and tube length. Make sure that the scope can't hit the top of turret when pointing straight up.

I am thinking of attempting to motorise the turrets this is complicated by the wheels being on the turret, if on the base then the motor could sit between the wheels.

The other change is to replace the hardboard running surface with something 'harder' to prevent the wheels settling in to the surface, making it difficult to start rotating. 

I hope that helps a bit, obviously any questions feel free to ask. 

Rob