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...
Yeh mine is good'ol manual, I had one before and yes the pier was off set for my Meade SCT on fork mount but with my NJP mount I am pretty sure I will be ok with a centred pier
Actually that's a good idea ... what's the life of styrofoam?
Cheers Matt, this was my exact plan and I may stay on this path but lay the plastic cheers
Yes, plastic it is what do you mean by stripping?
Why would I need an offset, I have a GEM isn't that centralised..?
Mike
I meant stripping out the formwork around the pier.
Was thinking it was necessary to have an offset to see the sky at the zenith. I did not know that the dome would already allow for that. Happy to be corrected.
Yep, pier for a GEM should be in the centre - dome slit goes past zenith. The necessary dome movements as you get to the zenith do get more radical though ... this depends on the geometry/offsets of the mount + scope combo and offsets with respect to the dome.
Mike, I placed a square of 50 mm thick high density foam (from Clark Rubber, and with a circular cutout for the pier)) on top of my pier foundation block prior to pouring the 100 mm thick slab. I did a test before I bought the foam to ensure that the weight of the concrete would not compress the foam.
The foam is there for keeps, and doesn't achieve quite 100% mechanical isolation but it's still pretty good - probably ~90%.
Regarding offsetting the pier, I agree with your thinking that you would just rotate the dome until the opening is above the scope. I offset my pier about 250 mm North because I had a fork-mounted scope originally. Even with that offset and now a much larger scope on a GEM, I can still always find a dome position to get a full look, although as Fred said, there are some pretty radical angles involved!
Ok, added the plastic to the base of the form-work...bit windy today (shock horror! ) so made it a bit tricky to get it down ...will trim the plastic a bit more closer to the pour and remember to take out all the weights ..hopefully that day won't be too windy
Thanks for all the tips boys
Chris, not sure what you mean actually..? You put the rubber "on top" of the pier base? Don't get it
Chris, not sure what you mean actually..? You put the rubber "on top" of the pier base? Don't get it
Mike
Mike - Unlike your pier foundation, mine was a large concrete block with its top below the circular slab level. There is a tall concrete pier on top of the concrete block, and the high density foam was placed on top of the block (with a cutout for the concrete pier) so that the circular slab, which was poured later, did not rest on the pier block. I will post a picture of the foam in situ when I find one. In retrospect, I think that your design is better in that you have less surfaces to mechanically isolate between the building and pier.
I placed my pier in the exact center of the dome as I have a GEM mount. The slit for the dome opens past the zenith and if you automate the dome and measure everything correctly then when you automate the dome rotation ( not the slit automation) then its a real joy to watch the dome track the scope and it goes perfectly across the meridian. I bit of a laugh as it does a meridian flip but tracks it perfectly. If you do automate the dome then remember to get an ATEN serial to USB connector for the electronics as that's the only one that works -good old yanks (Maxdome) have yet to make it USB.
Allan
I placed my pier in the exact center of the dome as I have a GEM mount. The slit for the dome opens past the zenith and if you automate the dome and measure everything correctly then when you automate the dome rotation ( not the slit automation) then its a real joy to watch the dome track the scope and it goes perfectly across the meridian. I bit of a laugh as it does a meridian flip but tracks it perfectly. If you do automate the dome then remember to get an ATEN serial to USB connector for the electronics as that's the only one that works -good old yanks (Maxdome) have yet to make it USB.
Allan
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No Automation planned at this stage Allan...but I guess you never know
It's the night before the concrete arrives, all is ready and weather looks favourable for tomorrow....first concrete slab I have ever attempted (and I am even 1/2 Italian!!) so fingers crossed I get it right
Took the afternoon off work and Riley and I did the Italian thing....
I remembered that we have a few kangaroos that come in around our house at night and I forgot to plan for this bit ...so a very rudimentary barrier will hopefully deter them
lookin good Mike. dont let it bake too much in the sun, keep it wet for a few days to cure slowly.
Josh
It is pretty cold here at the moment, near zero over night and around 15C during the day..?
How and when would you suggest I start wetting it? It's still soft so I was going to wait until it was hard enough not to get water drop marks ie tomorrow morning, or is that too late?
It is pretty cold here at the moment, near zero over night and around 15C during the day..?
How and when would you suggest I start wetting it? It's still soft so I was going to wait until it was hard enough not to get water drop marks ie tomorrow morning, or is that too late?
Not a 100% Italian yet...
Mike
use a hose, or even a small sprinkler. when it dries out wet it again. Its not super critical, just to prevent it drying out too fast. tomorrow isnt to late, do make sure the concrete has gone off though - dont want to get onto it to early.
Yes tomorrow morning is right for the first wet down. If you can keep it green for two days and use some plastic over the top of the water if you can. It will help prevent cracking. Strip the form on the third day and keep it a little wet for the next day or so after that.
Just a thought, we did a basketball area a couple of years ago at this time of year. We covered it with some plastic and old blankets to prevent any water component freezing before it cures properly. It sounds a bit excessive and may be rubbish but it is forecast for -1 tonight; probably even less out of town.
BTW, I'm really enjoying watching the process and suggestions as I'm planning a ROR obs at the moment, and thus far it's a pretty similar process (except for the shape of the slab!)
Shivers, I have to get up at 5am (6.30am start) and it will be close to freezing then (if not below) I might be able to get Riley to wet it later in the morning around 11am (when he gets up - he works late) will that do? It is predicted to rain after that anyway.
... what's the life of styrofoam?
) so made it a bit tricky to get it down 
...will trim the plastic a bit more closer to the pour and remember to take out all the weights 
...so a very rudimentary barrier will hopefully deter them 
