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Rusted

observatory
DIY rotating Nissen Hut or Pulsar 2.7m?

17 posts in this topic

Hi Guys

New member, ancient ATMer.

I have joined to directly access Pulsar dome owners' fund of information.

I am building a raised platform 8' off the ground to provide a much bigger sky.

Trees and hedges surround and interrupt our dark rural property.

Our modest 1.5 story home is on the southern border of our large garden.

Fortunately neighbours with security lights at a hundred yards south and SW are safely hidden by the house.

Increasing age demands shelter from the almost constant wind.

My two main OTAs are now much too heavy for easy lifting:

I am using a chain hoist and nested stepladders!

I have a 10" f/8 reflector with premium optics and a 7" f/12 R35 iStar refractor. [Presently folded.] Both ATM builds.

My almost completed, massive DIY GEM has 2" shafts and lots of heavy aluminium. ie. Immovable!

It is running AWR IH2/ASCOM drives to 11" and 8" Beacon hill wormwheels.

The images show my mounting on a temporary test stand.

 

Now the real reason for my unscheduled interruption: [Much as I like talking about myself.] ;)

I am torn between a DIY all aluminium, rotating "dome" of the cylindrical roof variety or buying a Pulsar 2.7m. dome only kit.

Making a hemispherical dome is a long term exercise in geometrical and sealing frustration IMHO.

The off-the-shelf Pulsar 2.7 is rather cramped for my 2 meter long Newtonian even when the dome is mounted on a much larger "box".

Does any recent Pulsar 2.7m dome purchaser have the minimum internal dimensions between opposing quadrant ribs?

I understand the 2.7m is actually 2.6 from Pulsar's own drawings but that may be external.

With so little clearance available I really need an accurate figure.

Thank you for your patience if you have reached this far.

Regards,

Rusted

 

58cfa270df0e9_P1270166rsz500.JPG.04757ea1f51de7692c0c42bb2e768ba0.JPG58cfa1fbd7ae7_P1270160rsz500.JPG.d01f8d8663ee7d2f478d159f4f3c478f.JPG

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I have built several domes and half cylinder "Nissen" style observatories. The latter type are cetainly easier to make and cost less in materials. I have a 8.5" F12 refractor in one and a 16" SCT in another, they have worked well for several years. The main construction is in aluminium and all bearings are stainless, the guide rails for the bi-parting sliding doors run on stainless steel tubing. Pictures on the front page of the Astronomy Centre website.  :icon_biggrin:

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4 hours ago, Peter Drew said:

I have built several domes and half cylinder "Nissen" style observatories. The latter type are cetainly easier to make and cost less in materials. I have a 8.5" F12 refractor in one and a 16" SCT in another, they have worked well for several years. The main construction is in aluminium and all bearings are stainless, the guide rails for the bi-parting sliding doors run on stainless steel tubing. Pictures on the front page of the Astronomy Centre website.  :icon_biggrin:

Hello, Peter,

Your reputation precedes you. :icon_biggrin:

Are there lots of detailed images online of the barrel roofed observatories? I wouldn't want to put you to the trouble of posting loads of images.

My feeling is that an up-and-over shutter is better in my breezy situation. The semi-cylindrical roof readily lends itself to such an arrangement.

The shutter can also be partially lowered. While the bi-parting shutters must be always wide enough not to stop down the telescope.

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There are more pictures on the website. The half cylinders are in four parts, the two outers are fixed and the two inners are the sliding doors. The sliding doors have housings each containing groups of three small bearings which in total form the effect of linear bearings when sliding on the guide tubing, I found this arrangement easier to operate and more robust against the strong winds that we experience. The sliding doors only pass over the zenith so that the telescope can be used overhead unobstructed, the rest of the cylinder is covered.  

I also have built a few folded 8" refractors, your design looks very interesting as does your fine equatorial mount.  :icon_salut:

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Hi Peter

Praise indeed, from the Master himself.  :blush:

Thank you for the further details of the half cylinder observatories.

My own reading of online opinion on bi-parting shutters is that they acted like sails.

Particularly in comparison with the more "flush" and symmetrical up and over design.

Since your observatories are sited on an open moor I must bow to your direct, hands-on knowledge and long experience. 

I am steadily working my way though your website images to find closer views.

The pure half cylinder has the advantage of requiring very simple edge framing which could be DIY rolled from aluminium angle profile.

Required size and thickness of profile still an unknown.

With 2.5m x 1.25m x 1mm aluminium costing well over £100 [local equivalent] per sheet I have hesitated in getting cracking.

I can make a half cylinder 3m wide out of six full sheets including the up-and-over shutter. [My own personal choice.]

3m would give me "breathing room" for a stacked folded refractor/reflector in the the same black alloy framing.

But, is 1mm sheet sufficiently stiff once curved into a self supporting, half cylinder?

I'm trying to completely avoid any plywood since the weight rises so dramatically.

I would be working entirely alone, as usual, and must avoid heavy lifts at my age. [70]

The Pulsar 2.7 sounds as if the components could just be managed, working alone, in still air.

The problem with the 2.7 is likely to be the lack of clearance for so large, an asymmetrically mounted [GEM] OTA.

I am discussing the idea [with myself] on my blog:  These rough drawings are not strictly to scale.

 

 

barrel cylinder dome txt.jpg

dual ota txt 2.jpg

Edited by Rusted
oversized images

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Hello again "Rusted".

Without wishing to sway your design preferences, at this preliminary stage all things are open to consideration.

I think bi-parting doors become wind sails only when applied to domes and not cylinders. My doors fit exactly over the fixed parts when fully open so do not increase the footprint or the profile of the observatory. I have made up and over doors for domes but they have added problems to overcome. These are essentially the weight which has to be lifted in either direction from the zenith and having to have a separate drop down front section so that door can be passed over the zenith without its upper edge fouling the building at the rear. Waterproofing is another consideration.

Don't let age get in the way, I built my largest cylinder observatory single handed when I was at least 70!   :icon_biggrin:

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Hello Peter and thanks for continued patience with a fellow "retiree." :wink:

You are quite right, of course, that a cylindrical form will not notice the change in outline of a bi-parting shutter as would a hemisphere.

 

Abrupt change of direction: I am now looking at fiberglass, dome-shaped, calf rearing igloos.

At least three different but similar models available in Europe. Holm&Haue, Agritech.it and Eurosilos Igloo16.

Plus others in heat reflecting white or absorbent green. Expected life at least 20 years.

4.5m in diameter x 2.2m high. That's 14'6" in old money. They come in three GRP segments with a half circle open doorway.

I can mount my refractor and reflector together inside a 14'+ dome and still have change from half-a-crown. :hello2:

Closing the open doorway with reinforced plywood panel gives me a surface to fit a low access door and the beginnings of a slit.

Making a slit to the zenith will weaken the central segment but I can easily stiffen the structure on the inside.

The usual laminated plywood and rubber wheels for rotation, of course.

Any thoughts on this continuing lunacy? :icon_biggrin:

 

holm laue igloo 3 rsz 500.jpg

holm laue igloo assembly 2 rsz 500.jpg

holm laue igloo assembly 1 rsz 500.jpg

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An interesting concept, if the price is right it might well be worth a try. Many years ago I made a 8 metre dome converting a steel silo dome, the dome was straightforward enough but cutting a slit into it and making good for the door was a nightmare, glass fibre should be a lot more manageable.  :icon_biggrin:

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Hi again,

I'm getting more quotes from competing calf dome, manufacturer's agents today.

If I go ahead I should probably start a new build thread for the amusement of the assembled masses.

I have now ditched my original, square, 8' raised platform idea and will build a cylindrical support wall 8' high to provide a guarded 'veranda.'

This will provide a much larger, stabilizing footprint and "free" scaffolding to work from in much greater safety than ladders.

The cylindrical room below the dome floor will be accessed from a 'proper' door leading to safe, internal steps to a drop-down trapdoor.

I'm thinking of using pyramidal, adjustable, concrete, carport anchors for footings for the multiple support posts.

The ground of the intended dome site is soft garden soil which is two feet lower than the rest of the area.

After providing a compacted gravel bed for the anchors the area around these will be back-filled with more compacted sand & gravel.

This will save a lot of digging holes, mixing and laying heavy, wet concrete around deeply buried posts and will simultaneously match the site's ground level.  :thumbsup:

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Sorry, Guys.

I have just discovered the 4.4m calf dome weighs 485lbs!

Which makes each of the three segments 160lbs.

I think this is far too much for one elderly person to manhandle.

Particularly since there is so much modification to carry out.

Then lifting it onto a platform 8' off the ground!

It might be possible to hire a machine for the lift, but it's still a lot of very heavy work.

So it's back to the Porsa 2.7. Or an aluminium, half cylinder.

For those interested I was looking at  between £2500 and £3000 for the calf dome, delivered.

No doubt your local prices are quite similar if you are interested in such a project.

 

 

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While the Pulsar 2.7 provides just enough clearance for the 10" f/8 it denies me the ability to use my 7" f/12 refractor in its long tube.

I would be stuck forever with the folded arrangement while I prefer the wonderful sense of scale with the classical, long tube refractor.

So it looks like I'm building an all aluminium "barrel vaulted" observatory similar to the Astronomy Center examples.

One made out of aluminium sheet and gently curved angle profile of a minimum 3m [or 10'] square.

Being a farming area I can probably arrange a lift of the completed observatory onto the 8' tall supporting structure.

That would allow me to do all the 'dome' building work with much greater safety, speed and ease down on ground.

I can obtain full sheets of aluminium 1m and 1.25m wide x 2, 2.25 and 3m in length.

Now I'd be most grateful for some pointers to suitable sheet thickness and alu. angle profile dimensions.

What is the preferred method of fastening these materials together? Pop rivets, self-tapping, or stainless steel nuts and screws?

Thank you for your continuing patience.

 

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No time like the present. I know of a small engineering firm who kindly supplied me with sheet aluminium for my folded refractor. 

So I just cycled 24 miles to place an order for the gentle bends on some 40 x 40 x 3mm angle profile aluminium for the edges of my planned 3m square barrel [?] observatory. :thumbsup:

I have also ordered enough angle profile to complete the rest of the framework. Then comes the sheet metal work and the shutter. 

I'm hoping Peter will share more information on his 'linear' bi-parting shutter bearings before I get to that point.  :)

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Hi Horwig

Thanks for the excellent suggestion.

The idea had not escaped me and I have researched extensively for available sizes and shapes.

It has the advantage of being widely available and its familiarity readily 'disappears' into the rural, farming landscape.

The downside is heat absorption of dark green paint compared with much more desirable white.

Or brush painting it white afterwards and ending up with a peeling eyesore beyond reach for 'redecoration.'

The worst feature, though, was the weight. Which has many ramifications for support and manual rotation.

Working alone and lifting heavy corrugated steel sections onto a dome, with a floor height of 8' isn't easy at my age. [70]

Aluminium may not be as stiff as steel but it does have the desirability of being lighter to handle and is much easier to work with.

It is also naturally reflective when naked and very long lasting 'cosmetically' where access for cleaning is so difficult.

 

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Agree with you regarding weight, but as to colour, that place I found seems to supply all kinds of colours, and, importantly, they can supply the sheets with an anti condensation liner

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Thanks, but I don't live in Gravely Blighted.

So the postage costs to Denmark might be a bit steep.

Great idea though. :thumbsup:

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