Critique my Obsy design...

[CraigT82]

Just starting to think about designing and building my first obsy to house my EQ6 mounted fullerscope (and then a 12" f5 newt in the near future).

I've come up with a preliminary design for the framework and general outline of what I want, though having never done this before I'm not sure if I'm going wrong. Not decide on what would be going on the outside, probably T&G, and a ply roof.

My first priority is general sturdiness, I want it to be solid and fairly simple too. I also want low walls to give decent views down to around 15 degree alt hence the low height of it! The door is pretty low but as I'll only be going in there a couple dozen times a year at best I'm not fussed about that.

Please take a look let me know what you'd do differently!

8x8 Observatory-Framework.pdf

[pete_l]

20 minutes ago, CraigT82 said:

 I'll only be going in there a couple dozen times a year at best I'm not fussed about that.

Ah, an optimist!
A 12inch F/5 newt is 5 feet long. And the balance point is quite a long way towards the rear. With my 30cm F/5 dob there is 90cm from the balance point to the top of the tube. And more distance if you have a dew shield after that,
I'd say that 8 feet (2.4m) inside measurements  is right at the lower limit of what you'd need.

[Owmuchonomy]

Based on first hand experience I wouldn't recommend sinking the posts (or anything except the pier block) of the main building below ground.  I would sit the corner posts on 8"x2" 'skis' and leave 150mm between floor and ground.  In that way damp and condensation are eliminated especially if you leave a gap behind the roof lap to allow air flow.  Sinking the run off posts is fine as they will have to support the roll off roof but are remote.

[CraigT82]

14 minutes ago, pete_l said:

Ah, an optimist!
A 12inch F/5 newt is 5 feet long. And the balance point is quite a long way towards the rear. With my 30cm F/5 dob there is 90cm from the balance point to the top of the tube. And more distance if you have a dew shield after that,
I'd say that 8 feet (2.4m) inside measurements  is right at the lower limit of what you'd need.

Yeah and my fullerscope is actually longer than that so may need to think about going up to 10ft x 10ft. Is there any kind of calculator anywhere to calculate the 'swing' area of an eq mounted scope?

6 minutes ago, Owmuchonomy said:

Based on first hand experience I wouldn't recommend sinking the posts (or anything except the pier block) of the main building below ground.  I would sit the corner posts on 8"x2" 'skis' and leave 150mm between floor and ground.  In that way damp and condensation are eliminated especially if you leave a gap behind the roof lap to allow air flow.  Sinking the run off posts is fine as they will have to support the roll off roof but are remote.

Thanks, is that because the corner posts would gradually soak up moisture through the concrete? 

[Craney]

I'm very envious of anybody building an observatory. It's looks good.

A small point, might not be anything, but the high side of the roof  slope is facing West, which will catch more wind in the UK than if facing East.

If you switched it around then the slope will be more aerodynamically  placed in terms of the prevailing wind  ( Nor & Sou'Westerlies) and might stop any strong gusts getting under the higher end.

Obviously there may be other local factors that are more important to have it the way you have.

 

Sean.

Edited August 25, 2020 by Craney

[Owmuchonomy]

4 minutes ago, CraigT82 said:

Yeah and my fullerscope is actually longer than that so may need to think about going up to 10ft x 10ft. Is there any kind of calculator anywhere to calculate the 'swing' area of an eq mounted scope?

Thanks, is that because the corner posts would gradually soak up moisture through the concrete? 

Potentially, or from the surroundings.  It may be fine as you quote treated posts, but I found it best to get everything above ground.

Edited August 25, 2020 by Owmuchonomy

[CraigT82]

14 minutes ago, Owmuchonomy said:

It may be fine as you quote treated posts, but I found it best to get everything above ground.

Hmm  wondering if anyone has built their obsy on heavy duty deck blocks? These look good especially with the RC beams to go on them...

 

 

https://www.wrekinconcreteproducts.co.uk/products/concrete-beam-beam-block-system/

Edited August 25, 2020 by CraigT82

[DaveS]

Don't make your door too low. I spec'd mine to be high enough that I could walk through without having to duck, as I knew that otherwise I'd give myself a clonk on the head, especially leaving it at night. I've also run a string of red LEDs around the walls for lighting.

And for heaven's sake, don't make your rafters too light. I did and now I'm having to reinforce them as a stop-gap before a rebuild next year.

[CraigT82]

32 minutes ago, KevS said:

https://www.blackwaterskies.co.uk/2013/12/observatory-planning-and-german-equatorial-mounts/

try the above.

K

Thats fantastic thanks for sharing.

 

27 minutes ago, DaveS said:

Don't make your door too low. I spec'd mine to be high enough that I could walk through without having to duck, as I knew that otherwise I'd give myself a clonk on the head, especially leaving it at night. I've also run a string of red LEDs around the walls for lighting.

And for heaven's sake, don't make your rafters too light. I did and now I'm having to reinforce them as a stop-gap before a rebuild next year.

What timber did you start off with for your rafters? 

[DaveS]

Very light, 25x38mm nominal, so I have some steel coming tomorrow. When I rebuild I'll use the 45x70mm timber that I used for the roof bearers, which may get an upgrade too.

[Yawning Angel]

6 hours ago, CraigT82 said:

has built their obsy on heavy duty deck blocks

I built mine on 6 concrete curb stones corners, which look similar. They are the 90 degree blocks for inside corners

[Seelive]

I had a 10" F6 so the tube length is the same and 10' between the walls was just sufficient to avoid getting 'trapped' on the eyepiece side of the scope when being used at lower altitudes.

How are you intending to support the mount? I wouldn't consider using the wooden floor to support it. I had a concrete block (set into the ground) with top level with the floor but isolated from it so that any floor movement wasn't transferred to the mount. 

[ollypenrice]

Like the others I'd avoid sinking timber into the ground. I'd use raised blocks or, ideally, poured concrete to keep the timber out of the damp.

Roofing material: I've used all sorts and gravitated unconditionally towards corrugated steel. It may not be the prettiest solution but it is foolproof and effectively everlasting. It can be bolted down with no-nonsense bolts, it doesn't tear or sag or degrade in the sun and it is gradually replacing all the other systems I've tried on our sheds. It works. The rest work for a while...

Anti-lift: this is very important indeed because roofs love taking flight. I would make the roof wider than the walls and give it sides which come down below the tops of the walls. You can put batons along the roof sides below similar batons on the walls. This means you don't have to remember to use fixing devices. The roof won't be able to lift.

While tongue and groove or shiplap are popular my own preference is for marine ply.

1) It makes construction ludicrously easy. You take a ply 'wall,' possibly cut to size by your supplier. Long walls might need two panels but the principle remains. You screw your structural timbers around the border (usually 5x7cm here in France) and you cut triangles of ply to reinforce the inside corners. Once you've made four of these walls you have, in effect, four box sections which simply screw together to make the shed. The ply itself doesn't need to be thick or load bearing. Its role is to keep the structural timbers aligned.

2) It is easy to maintain. If, eventually, the ply sides start to look grotty, you can unscrew them and replace them or - even easier, simply cover them with a new panel of the thinnest marine ply you can find.

Here's an example:

The foreground shed is a small robotic one, the one behind a 3x4 metre multi-panel equivalent.

The imaging shed below has a 2.2 metre square footprint, not including the warm room. It really is too small for visual use. I'd want 2.5 metres as a bare minimum.

Have fun!

Olly

[CraigT82]

On 25/08/2020 at 16:56, Craney said:

small point, might not be anything, but the high side of the roof  slope is facing West, which will catch more wind in the UK than if facing East.

That's a very good point and definitely something for me to consider, thanks! 

 

13 hours ago, Seelive said:

I had a 10" F6 so the tube length is the same and 10' between the walls was just sufficient to avoid getting 'trapped' on the eyepiece side of the scope when being used at lower altitudes.

How are you intending to support the mount? I wouldn't consider using the wooden floor to support it. I had a concrete block (set into the ground) with top level with the floor but isolated from it so that any floor movement wasn't transferred to the mount. 

Yes I've just done the calcs and we have a whopping 1152mm radius of swingqith the Fullerscope so 8x8 is not gonna cut it! Pier will be steel most likely, bolted to concrete block in the ground through hole in floor. 

 

9 hours ago, ollypenrice said:

Roofing material: I've used all sorts and gravitated unconditionally towards corrugated steel. It may not be the prettiest solution but it is foolproof and effectively everlasting. It can be bolted down with no-nonsense bolts, it doesn't tear or sag or degrade in the sun and it is gradually replacing all the other systems I've tried on our sheds. It works. The rest work for a while...

Anti-lift: this is very important indeed because roofs love taking flight. I would make the roof wider than the walls and give it sides which come down below the tops of the walls. You can put batons along the roof sides below similar batons on the walls. This means you don't have to remember to use fixing devices. The roof won't be able to lift.

While tongue and groove or shiplap are popular my own preference is for marine ply.

1) It makes construction ludicrously easy. You take a ply 'wall,' possibly cut to size by your supplier. Long walls might need two panels but the principle remains. You screw your structural timbers around the border (usually 5x7cm here in France) and you cut triangles of ply to reinforce the inside corners. Once you've made four of these walls you have, in effect, four box sections which simply screw together to make the shed. The ply itself doesn't need to be thick or load bearing. Its role is to keep the structural timbers aligned.

2) It is easy to maintain. If, eventually, the ply sides start to look grotty, you can unscrew them and replace them or - even easier, simply cover them with a new panel of the thinnest marine ply you can find.

Thanks Olly those are very good suggestions. I particularly like the anti-lift roof design. The outside of mine will probably be covered on the outside in artificial living wall which goes on easy and looks great (and will be a key condition from my wife in exchange for permission to build!). My garage is covered in the stuff and it really improves the look. Will most likely go with plywood of some sort over the framework.