You realise with the dome slit with your 12 inch aperture you will have to move the dome around every 25 minutes or less (depending on where you are pointing).
I had a 12 inch scope with a 2.3 sirius and it is tight fit aperture wise, and that was with automation moving the dome every 5 minutes.
Not a problem if you get an Astrohaven Clamshell Observatory
Lol Mike! To build an observatory is one thing - but doing it with such effortless grace as you display here is something we mere mortals can only dream of
Ahh grace....?
Quote:
Originally Posted by alistairsam
well said Rolf, he makes it look so easy, that includes the gymnastics!
being a rental property, how did it go with the landlord and what would you do with the 500kg of concrete if and when you leave?
cheers
Alistair
Asked the landlords for permission to lay a slab and since the dome goes when we leave, just leaving a nice 2.5m circular pad behind for a water tank, garden chairs patio, what ever, they said ok. It is located away from the house and somewhat out of sight and I will do a neat job plus it is a rural 200 acre property after all with an old site shed, stable and crude paved areas and crappy poor concrete laid in the past for horse stable areas etc by the previous tenants and owners, so it's not like a residential property I guess
Quote:
Originally Posted by Steffen
Do you have to ask? He picks it up and puts it on the back of the ute, of course
Not a problem if you get an Astrohaven Clamshell Observatory
They do look awesome...but I question their effectiveness in a stiff breeze, I think a dome offers more protection in that instance as well as warding off dew and ice more effectively..?
Never done slab form-work before, so hey, thought I'd start with a circular
slab juuust to test our skills. It's a 2.6m diameter circle for a 2.3m Sirius
Observatory so there will only be a 6" strip of concrete around the base of the
building to minimise the amount of thermal mass exposed to the sun.
+1 on the plastic underneath. Also you could remove the formwork around the pier base and replace it with self adhesive ableflex instead saves having to mastic the gap later. albeflex is a closed cell foam with adhesive on one side and a 10mm perforated strip on the top edge. after the concrete has set you remove the 10mm strip off the top and then apply a sealant mastic to just that 10x10mm gap.
You really should put plastic under the slab, or you are going to have big moisture issues.
Yeh, I considered that but a friend who does concreting thought it unnecessary for such a small job...but you may be right wouldn't be hard to add it....thanks Brett, leave it with me
+1 on the plastic underneath. Also you could remove the formwork around the pier base and replace it with self adhesive ableflex instead saves having to mastic the gap later. albeflex is a closed cell foam with adhesive on one side and a 10mm perforated strip on the top edge. after the concrete has set you remove the 10mm strip off the top and then apply a sealant mastic to just that 10x10mm gap.
Cheers re the plastic, probably will do that
I considered able flex too but couldn't find the right width to match the 110mm slab ...so I decided to make it a completely empty space = no way for the main slab to touch the pier footing..? Whad-a-ya recon?
I considered able flex too but couldn't find the right width to match the 110mm slab ...so I decided to make it a completely empty space = no way for the main slab to touch the pier footing..? Whad-a-ya recon?
Mike
I used some left over Styrofoam from the observatory materials and cut it to to the width and height of my pier base, placed it around it and taped it there. It now stays there. Fills the gap and doesnt transmit any vibrations. It was about 20mm thick.
As long as you can still get the formwork out after the pour. In this case I would fill the void with polyurethane foam (just like the foam used in foam mattresses) strips from Clark's Rubber in newcastle street F/wick. Set the foam down so it is about 5 to 10mm below top of concrete then on top of that you run a bead of flexible sealant to water proof the join. That way you have a sealed join but vibrations won't be transferred to the pier. (this system is used in buildings where concrete panels abut each other).
Agree with the plastic and foam, it will make it easier for stripping etc. Just also have you offset the centre of the pier to the slit opening? You said you have about 200mm so you could offset later if you like.
I used some left over Styrofoam from the observatory materials and cut it to to the width and height of my pier base, placed it around it and taped it there. It now stays there. Fills the gap and doesnt transmit any vibrations. It was about 20mm thick.
Josh
Actually that's a good idea ... what's the life of styrofoam?
Quote:
Originally Posted by Kunama
As long as you can still get the formwork out after the pour. In this case I would fill the void with polyurethane foam (just like the foam used in foam mattresses) strips from Clark's Rubber in newcastle street F/wick. Set the foam down so it is about 5 to 10mm below top of concrete then on top of that you run a bead of flexible sealant to water proof the join. That way you have a sealed join but vibrations won't be transferred to the pier. (this system is used in buildings where concrete panels abut each other).
Cheers Matt, this was my exact plan and I may stay on this path but lay the plastic cheers
Quote:
Originally Posted by Paul Haese
Agree with the plastic and foam, it will make it easier for stripping etc. Just also have you offset the centre of the pier to the slit opening? You said you have about 200mm so you could offset later if you like.
Yes, plastic it is what do you mean by stripping?
Why would I need an offset, I have a GEM isn't that centralised..?
Why would I need an offset, I have a GEM isn't that centralised..?
Mike
I think Paul means when you point your scope at the zenith without an offset, you will be looking at the inside of the dome. So offset it a little so you can see through the slit. You said you had 6 inch's on the outside to do that.
Styrofoam - lasts for ages, its not readily biodegradable.
I think Paul means when you point your scope at the zenith without an offset, you will be looking at the inside of the dome. So offset it a little so you can see through the slit. You said you had 6 inch's on the outside to do that.
Styrofoam - lasts for ages, its not readily biodegradable.
Josh
Cheers Josh...a good idea re the foam, it is rigid too so will stay in place for the pour easily.. I will consider that.
Off set huh..? Hmmm? wouldn't I just rotate the dome...?
Cheers Josh...a good idea re the foam, it is rigid too so will stay in place for the pour easily.. I will consider that.
Off set huh..? Hmmm? wouldn't I just rotate the dome...?
Mike
Hey Mike,
I even left my foam in, it seems OK, It will be really hard to get out after a pour.
If you rotate your dome, you will still not be able to see through the zenith, rotating won help move it out the way, the slit has to go past the zenith point of your scope
Hey Mike,
If you rotate your dome, you will still not be able to see through the zenith, rotating won help move it out the way, the slit has to go past the zenith point of your scope
Josh
The dome slit does go past the the zenith on the Sirius domes..? So I just can't see the problem...am I missing something
That's an interesting problem. Thinking of the OTA pointing as it reaches the zenith (not from experience). As Mike says, it doesn't matter how much the offset is, theres always a dome slot rotational spot the OTA can peer through, but the more the offset the more radical the rotation becomes as the zenith is approached.
Id say the pier should be in the middle because if say you have an offset to cover the mount leaning hard east, then its way out if its west before a flip.
As Mike says, it doesn't matter how much the offset is, theres always a dome slot rotational spot the OTA can peer through, but the more the offset the more radical the rotation becomes as the zenith is approached.
I have no experience with domes or automation... but out of curiosity, how does the typical dome automation software handle this?
The dome slit does go past the the zenith on the Sirius domes..? So I just can't see the problem...am I missing something
Mike
The shutter goes past the zenith a far way in manual shutter. In the auto shutters they do not go as far back.
I think the poster was confused about having an offset when using a fork mount or using a pod type dome with obstructed zenith. With a gem stick it in the middle of the dome. There is a formula for where the declination meets the ra axis as the centre point of the dome... I can't remember where I read it...
...so I decided to make it a completely empty space = no way for the main slab to touch the pier footing..? Whad-a-ya recon?
... hope Paul didnt mean something else..
