ROR observatory floor options

[Allan]

I'm going to build a ROR obs for a dob and I'm weighing up whether to build the floor with concrete or timber bearers.

I built a house with a waffle pod slab and it's very easy to do the same with the obs, but I'm very wary of the thermal heat that's stored in the concrete. I'm worried it will mess up the seeing for an extended period while it slowly cools to ambient.

With the timber floor I see no such issues with thermal management.

I'm sure I'll find a heap of useful information once I start trawling through all the threads here, but for now, what is the consensus around the best material to construct the floor with.

[glend (Glen)]

Allan my ROR obs is built on timber bearers sitting on treated pine post footings set (600mm deep) in concrete. There is an air space under the floor to allow circulation, and the ground underneath is covered by weedmat and a layer of gravel on top, this keeps it dry and prevents weed growth near the edges. The floor is heavy tongue and groove structural ply flooring panels. And your right there are no thermal issues to contend with. The question is how heavy is that big dob going to be, and what steps are required to make the floor strong enough to support it? With my setup i use a concrete pier to support my EQ mount, and this pier rises up through the floor cutout - the pier was obviously constructed first and the obs built over it. Interestingly when i recently bought a new mount (Celestron CGX), i set it up in the obs on its tripod for initial testing, because i was waiting for a new pier adaptor to arrive. The tripod and mount head combo are pretty heavy but the obs floor structure had no problems supporting it with no vibration or PA consequences due to weight shifts while slewing. I even did some long exposure image testing and it worked fine. You want to avoid walking around it while imaging but i could supervise it from the house using Teamviewer. For a purely visual setup it would have been fine. Based on the CGX combined weight plus the scope and imaging gear, it easily weighed more than my old 16" dob, so structurally there is no reason a large dob cannot be used in that type structure.

Considerations, do you want to roll it out to a pad as a consideration? This would not require a ROR. A ROR built for a dob may have to have lower walls to allow the low slung dob to get down to lower altitudes, which is not an issue for high mounted EQ setups. A Roll-out building can be less complicated to build than a ROR one, just open the barn doors and roll out the dob to a small concrete pad. As we know in places like Bretti, the land can take some time to cool down, especially in the warmer months, and this is probably a greater impediment to ideal seeing than a small concrete pad immeadiately under your dob. In fact a small concrete pad might be useful for dew prevention in cooler months as it would release its stored heat beneath the optics gradually.
Just a few thoughts. Good luck with the project and we will want photos.

[el_draco (Rom)]

I'm building a ROR at the moment. I'm using 150mm C section set at 500mm separations. The whole thing is mounted on "mega anchors" and about 300mm off the ground. Its all bolted together using plates you can buy from Bummers.

Framing is about done and its really solid. Not a drop of conc on site, apart from the pier. Thermal mass is going to be very low for the size of the building (9m X 4m inc warm room). I recommend you investigate this option.

[xstream (John)]

Allan,
I would use 18mm compressed sheet. You should have virtually zero thermal issues with it but you would require a substantial sub structure, as compressed sheet is very heavy.

[Allan]

Originally Posted by glend

Allan my ROR obs is built on timber bearers sitting on treated pine post footings set (600mm deep) in concrete. There is an air space under the floor to allow circulation, and the ground underneath is covered by weedmat and a layer of gravel on top, this keeps it dry and prevents weed growth near the edges.

Thanks Glen, this is exactly how I built my little fellas play house in the back yard, and was how I thought I would do the obs floor. But these Mega Anchors sound neat.

[Allan]

Originally Posted by el_draco

I'm building a ROR at the moment. I'm using 150mm C section set at 500mm separations. The whole thing is mounted on "mega anchors" and about 300mm off the ground. Its all bolted together using plates you can buy from Bummers.

Framing is about done and its really solid. Not a drop of conc on site, apart from the pier. Thermal mass is going to be very low for the size of the building (9m X 4m inc warm room). I recommend you investigate this option.

These Mega Anchors sound like a good idea. I might have to consider going down this route. Thanks for the info.

[Allan]

Originally Posted by xstream

Allan,
I would use 18mm compressed sheet. You should have virtually zero thermal issues with it but you would require a substantial sub structure, as compressed sheet is very heavy.

I used compressed sheet for the second floor wet areas when building my house, and that was what I intended to use. I agree it's good stuff, especially for an obs floor.

[ausastronomer (John Bambury)]

Hi Allan,

Your spending a lot of money on the scope so I think its worth over specking your observatory a touch to make sure it works really well. If you have some headroom in your budget.

While thermal management is critical with a large scope its equally important to make sure you have no movement in the floor whatsoever. No point having good thermals enabling you to get to high magnification, only to have this compromised with some movement in the floor.

Timber will work really well but you need to make sure its really well seasoned and not going to shrink. I haven't seen those "mega anchors, so I can't comment on those.

Consider using short brick piers, consider reducing the space between centres on both your floor joists and bearers. Consider going up one size in the dimensions of both your floor joists and bearers. Consider using 25mm compressed fibre cement sheet, or 25mm compressed chipboard for the flooring. I always think its way better to spend a few extra dollars and way over engineer something in the beginning, as opposed to spending a large amount of dollars retro fixing something that doesn't do what it was designed to do.

Cheers,
John B

[Allan]

Thanks John, yes I'm going to put a fair bit of effort into the floor.

[el_draco (Rom)]

Originally Posted by ausastronomer

While thermal management is critical with a large scope its equally important to make sure you have no movement in the floor whatsoever. No point having good thermals enabling you to get to high magnification, only to have this compromised with some movement in the floor.

Movement in the building should be irrelevant. The scope itself should be mounted on a pier that is isolated from the structure altogether. If its attached to the building then wind gusts could cause vibration.

[glend (Glen)]

Originally Posted by el_draco

Movement in the building should be irrelevant. The scope itself should be mounted on a pier that is isolated from the structure altogether. If its attached to the building then wind gusts could cause vibration.

It's a dob, no pier. But what you say is true for EQ mounts

[el_draco (Rom)]

Originally Posted by glend

It's a dob, no pier. But what you say is true for EQ mounts

I'd still build a pier for future proofing alone. A good option for you may be to try out a plate called a "Surefoot". Its a variant on the mega anchor. I've contemplated using one of these instead of a pier and may do so with my next scope. If they are anywhere near as rigid as the mega anchors I suspect it'll do the job. Digging a bloody great hole and filling it in with concrete is a pain in the proverbial for many reasons but digging the hole between bearers would be an order of magnitude more irritating. A surefoot would also be better environmentally I as well.

[glend (Glen)]

Originally Posted by el_draco

I'd still build a pier for future proofing alone...... Digging a bloody great hole and filling it in with concrete is a pain in the proverbial for many reasons but digging the hole between bearers would be an order of magnitude more irritating.

Most people would put the pier footing in first, then build over it. I would agree, having at least a footing there could be useful. Given his investment in Taks, he may wind up imaging.

[Kunama]

Allan, I would suggest that if you're going with timber or cement sheeting for the floor then you should build the middle section (about 1000x1000mm) completely separate from the walking floor. You can make the scope support using 4 mega anchors supporting bearers and joists, then sheet over it with 18mm compressed sheet. Build the rest of the floor so it is completely isolated from the scope pad.

At a focal length of 2700mm using any decent magnifications on a continuous floor you will get vibrations that will drive you nuts.

[Allan]

Originally Posted by Kunama

Allan, I would suggest that if you're going with timber or cement sheeting for the floor then you should build the middle section (about 1000x1000mm) completely separate from the walking floor. You can make the scope support using 4 mega anchors supporting bearers and joists, then sheet over it with 18mm compressed sheet. Build the rest of the floor so it is completely isolated from the scope pad.

At a focal length of 2700mm using any decent magnifications on a continuous floor you will get vibrations that will drive you nuts.

Thanks Matt, that is exactly the conclusion I arrived at. If I have a few people in the obs, I can see how them moving around will cause movement through the eyepiece. So I've decided to build a centre section for the dob to sit on using timber and compressed sheet for least thermal mass, and then a separate floor section around it. Should do the trick.

[Allan]

Originally Posted by glend

Most people would put the pier footing in first, then build over it. I would agree, having at least a footing there could be useful. Given his investment in Taks, he may wind up imaging.

I have way too much fun doing visual astronomy, the thought of imaging never crosses my mind. Which is probably a good thing for the bank balance.

[ZeroID (Brent)]

Originally Posted by Allan

I have way too much fun doing visual astronomy, the thought of imaging never crosses my mind. Which is probably a good thing for the bank balance.

You are building an Ob, that is the first step .....
The slippery slope awaits ...

[bigjoe (JOSEPH)]

Our ol mate Dr C J R LORD'S god bless him!
http://www.brayebrookobservatory.org...E/BrayObs.html.
INTERSTING!
bigjoe.

[FlashDrive (Poppy)]

Originally Posted by Kunama

Allan, completely separate from the walking floor. Build the rest of the floor so it is completely isolated from the scope pad..

Well said .... good thinking..

Col...