How important is an isolated pier?

[MattJenko]

I understand how a concrete pier, sunk deep into the ground below any frost line and the column not being attached to the surrounding building would give the most stable platform for a telescope, but how important is this really? I have an outbuilding which is brick built with a concrete base and I have been pondering converting this to an observatory. I am thinking one or two breeze block columns sitting on the concrete base and a first floor ROR, but wondering how much I would be missing in terms of end result if I went the far more effort route and try and smash through the floor to sink in a more formal base.

Cheers

Matt

[Davey-T]

18 minutes ago, MattJenko said:

I understand how a concrete pier, sunk deep into the ground below any frost line and the column not being attached to the surrounding building would give the most stable platform for a telescope, but how important is this really? I have an outbuilding which is brick built with a concrete base and I have been pondering converting this to an observatory. I am thinking one or two breeze block columns sitting on the concrete base and a first floor ROR, but wondering how much I would be missing in terms of end result if I went the far more effort route and try and smash through the floor to sink in a more formal base.

Cheers

Matt

Guess it depends on your climate, the original idea of needing a couple of tons of concrete came from the USA where they like to do stuff on the grand scale, AFAIK the main reason is to maintain PA and possibly absorb vibrations if you live close to transport links or you personally wandering around it while imaging.

Plenty of folks image successfully with a tripod and I use a pier bolted to an existing patio with 6" of concrete under the slabs.

Dave

[Craney]

The question is ..... how bouncy is a concrete floor ??......  I am sure there are quite a few factors involved.    

But... before you start building up or digging down..... put a tripod on it, no vibration pads,  select a longish focal length say 1000mm ..... focus on a star, set the CCD to record an AVI....and watch what happens when you move around the scope, trying not to generate air currents or pressure surges too close to the OTA.   

If the star bobbles around like a jelly on speed  then you probably need to isolate the floor.   Unless... your plan is to be totally remote from the scope when imaging.

Obviously,  tracking errors, seeing and the like may dominate over any 'floor' wobble   and that is for you to judge, but you don't want to get your rig all up and running to suddenly decide that the original ideas of being over-engineered was the way to go.

Good luck.

 

[Tomatobro]

Some time ago I wanted to do some in and out focus checks using a "hubble" artificial star torch. This turned out to be an excellent test for checking mount and mount floor stability. So if you could fix one up say 15 or 20 metres away, place your mount where you propose and focus on the artificial star. Best is to place a camera in the scope so you can watch a monitor while you walk around the floor near the mount. If the image wibbles and wobbles then it gives you some idea of what to expect.

[Guest]

Like this? 🤔😂I'll get my jacket. 🙄

[fifeskies]

I used an existing brick outbuilding with concrete floor to convert to a ROR.

I made a wooden floor tied into the side walls but not resting directly on the concrete.

This wooden floor has a central hole cut out of it and there is a concrete block pier base placed onto the concrete underneath and then a metal Altair pier rising through the wooden floor cut out , pier fixed to the concrete block square direct onto the floor.

(Hint: cast the concrete bock pier anchor (with bolts in situ) before fitting the wooden floor.

Walking around on the "floating" floor does not seem to affect the scope in any way , any vibrations being damped out by the wooden floor and not transmitted to the slab below.

Will also be adding soft floor mats to the wooden floor (mainly for dropped eyepieces sake) , but this will also help dampen out any vibrations from moving around.

 

I can remove the pier and simply cover over the hole with new floorboards if I ever want to move the observatory out , leaving the anchor pier hidden below the floor , and return the space to just a shed.

 

 

Edited April 29, 2020 by fifeskies

[fifeskies]

Just to clarify , diagram of the floor I used

 

 

Edited April 29, 2020 by fifeskies

[fifeskies]

I used 4 x 2 beams for the floor and 25mm rough treated floorbords (cheap) overlaid with a sheet of 9mm ply to level it out smooth for the floor mats 

Edited April 29, 2020 by fifeskies

[MattJenko]

Thanks for all the input! I'll try out the tripod on base approach and see what happens. It is next to a country lane which has the occasional tractor going past, but nothing in the evenings. If all that means is to double check polar alignment periodically, hopefully I can just base pier on base.

[ollypenrice]

I just saw a bloke on FB drink a 1 litre bottle of vodka down in one. By next week someone will have made that two. This is my opinion of the internet mania for isolated concrete pillar foundations of many tonnes. I image at 0.9"PP with a pier plonked on the continuous floor of an observatory. It's a decent floor - maybe three tonnes of concrete, but that includes the warm room.

I have other, smaller, bases for scopes as well. One guy demonstrated that you could detect some movement at the EP if you stamped heavily around the telescope. True. And the solution might be...?

Our large four-scope remote observatory has a continuous floor of six tonnes. Nobody complains.

If you have a problem with trains, trucks etc passing, will a huge isolated lump fix it? The vibrations came to you through the ground...

Olly

[Magnum]

Mine isn’t isolated either  just a massive slab of concrete. I can pull myself up off the floor by grabbing the pier and my guiding graph doesn’t move LOL. 
I agree it can be overrated. It’s usually just 1 person in a home observatory anyway, not loads of people as with a public obs. And I know I’m not going to be jumping around in there when imaging, so I didn’t worry about it.

Lee

[7170]

I've seen lots of pictures on the internet where pier foundations are deeper and wider than those in your average two story house in the UK! Isolation can make sense as metal piers and setups can suffer from resonance and some people live in an area with a deep frost line so you can avoid having deep foundations everywhere in addition to the pier. But Lee above makes a valid point, how many times do you have a few people in your observatory when imaging, and how many times do you walk round the scope while imaging is in progress? And if you do everything remote from the house it matters even less.

If I were doing it again I would still have an isolated pier foundation. Not because of vibration but because it is easy to make a wood floor off the ground surrounding it after the initial pour (so things don't need to be 100% exact). And the observatory with a floating floor slightly off the ground will cool down quicker than an observatory where the whole floor is a single thick poured slab of concrete. But then in the past I had great success with a pier column made out of bricks and lots of people say that is a no no.

[pete_l]

1 hour ago, 7170 said:

observatory where the whole floor is a single thick poured slab of concrete.

Yes. My thoughts exactly.
My site has three telescope areas. Each of them is a poured slab about 15cm deep. The big one is reinforced with rebar mesh. The other two are about 1m across.

Here we get temperatures down to -12°C in the winter and I have never (in 4 years) noticed any movement due to frost heave. Nor when the summer gets up to 45°C and the soil dries out. I suppose that if I jumped up and down on the slab I might see some vibration in an image. But I have no intention of doing such a thing, so it is moot.
Occasionally I wonder how people who pour 1 tonne+ anchoring blocks ever intend to remove them before moving house. Or what the new owner's reaction is when they "discover" such a thing in what they assumed to be the lawn

 

[MCinAZ]

  I've put piers into three different observatories, and none was more than about half a meter in diameter and perhaps 800 mm deep. These were isolated from the surrounding floor, but if you already have a concrete floor in place, I'd give that a go and worry about an isolated pier only if it proves necessary. For short focal length work where you can limit vibrations from people walking around during critical times, you'll almost certainly be fine.

I've seen plenty of home observatories with a cubic yard of concrete underground. In almost all cases, the only benefits are to the concrete supplier and the owner's ego. What I find most amusing are the installations with literally tons of concrete supporting a mount on three 150 mm long pieces of 12 mm diameter threaded rod. Nothing says stability like putting a large, moving mass on a tuned structure.

[MattJenko]

This outbuilding is in inland southern france, so mild winters and hot summers. I see the view that isolation (at least in terms of piers rather than pandemics) is not represented well here. I hoped as much and will do some basic experiments myself and assume that if the building is stable enough, which it is, then its base will do for my modest astronomical observations. The piers (thinking of 2) will need to be about 8-10 feet high, but thinking brick chimney style would work well for me.

Thanks again, this forum never ceases to impress me.

[Dr Strange]

Speaking as someone in the US, there is a tendency to overbuild. However there is a need to do so in some of the colder climates. There is something called frost heave. That is where an upwards swelling of soil occurs during freezing conditions caused by an increasing presence of ice as it grows towards the surface. There is something called the 'frost line' where if you place a foundation below that line frost heave becomes much less of an issue. This is actually building code in the US in cold climates. It is taken from there. 

If you are in a colder part of the UK where deep soil frost and snow regularly occurs you need to take it into account when building your pier foundation. Otherwise over several years you will be facing redoing your PA and leveling (if you level things out) several times at best and could face the entire slab coming out of the ground at worst. 

As noted above there is a challenge with vibration if the pier is not isolated from the floor in some way. This can even occur with concrete slabs. It is amazing how much vibration can actually occur with just walking within a meter or two of the scope while imaging. This applies to hard surfaces other than concrete too. 

Edited May 19, 2020 by Dr Strange

[DaveS]

My 130 triplet apo is on a pier bolted to a concrete platform 1.5 x 2 x 0.5 m, and on occasion I've been on it when imaging and seeing no sign of vibration. The obsy I'm building is sat on a similar platform 2.2 m square and varying from 0.4 to 0.6 m thick. With foundations the builders reckon there's 8 tonnes or so of "stuff" in there.

As this is purely imaging and remote controlled there will be nobody in there when operational.

[MattJenko]

Isolation of the flooring itself if possible sounds like a good idea, but simply building pier on the existing base is how I am going to proceed - thanks.

[iapa]

14kg OTA, 20kg Mount on pier sitting on 60mm cubed of concrete

i just didn’t want it to fall over, vibration not an issue as it’s all remotel controlled from 15m away

[tooth_dr]

31 minutes ago, iapa said:

...sitting on 60mm cubed of concrete

The worlds smallest pier base 😂 cast in a Tupperware box? 
 

 

[iapa]

2 minutes ago, tooth_dr said:

The worlds smallest pier base 😂 cast in a Tupperware box? 
 

 

Well, as a Scot, must demonstrate the deep pockets/short arm syndrome 

[tooth_dr]

2 hours ago, iapa said:

Well, as a Scot, must demonstrate the deep pockets/short arm syndrome 

Even at that, 6cm x 6cm x 6cm is a little skimpy, did you mean 60cm!?

[iapa]

Of course I did

🤪😛😛
 

btw I’ve knocked things into while imagining e.g. small table - nothing happened 

Edited June 8, 2020 by iapa

[badgerchap]

I’ve a small extension of this question.

I live in the middle of nowhere with no road other than our drive (serving 10 houses) within about a third of a mile. Even this road is dead as a doornail past about 8 p.m., like, completely dead. I want a remote obsy in my garden, about ten metres from the house. I’m thinking that really, I don’t need to pour concrete AT ALL. In fact, apart from a sporadic need to redo the polar alignment, I think sticking my EQ6 tripod on a few slabs will probably do the job.

Now, anyone up for telling me how wrong I am?

EDIT: i should also mention I intend imaging at a pretty stumpy FL: 600mm at F4

Edited June 15, 2020 by badgerchap

[JamesF]

5 minutes ago, badgerchap said:

I’ve a small extension of this question.

I live in the middle of nowhere with no road other than our drive (serving 10 houses) within about a third of a mile. Even this road is dead as a doornail past about 8 p.m., like, completely dead. I want a remote obsy in my garden, about ten metres from the house. I’m thinking that really, I don’t need to pour concrete AT ALL. In fact, apart from a sporadic need to redo the polar alignment, I think sticking my EQ6 tripod on a few slabs will probably do the job.

Now, anyone up for telling me how wrong I am?

I'd prefer something that wouldn't move if it were bumped and I'd not lay the slabs on bare earth, but other than that I think it may well work just fine.

James