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Old 13-04-2019, 11:45 AM
benklerk
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Backyard obs planning

Just need some help and advice.

I'm planning on putting in a 3m x 3m shed to house a GSO 14" RC with either a mesu 200 mount or a JTW mount.

Anyway, Im going with a slab.
  • Slab first or pier first
  • How deep to I go with the pier
  • How high do I make the pier
  • What is a good size diameter for the pier
  • How much of a gap do I leave from pier and slab
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Old 13-04-2019, 01:23 PM
glend (Glen)
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I think a key question is how deep can you go before you hit rock. In the Blue Mtns there is a lot of rock around. Do you know what is under the surface where you want to put the obs. Some might argue for a good solid cubic metre of concrete for a pier footing, but if your pouring it on rock smaller might be better or drill the rock to stick some reo bar in there.
Are you thinking steel pier on a concrete footing or a concrete pier in a form with reo? If a concrete pier, a continuous pour from the footing is best. My pier is a continuous pour, wet on wet. You just leave enough setup time for the last footing pour to support the pier form and pour. I used a big PVC pipe as my pour form and left it in place because it provides a nice finish. Insert your J bars for your top plate as you finish the pier pour. You can buy the J bars at Bunnings, they call them foundation anchors I think, near where the reo stuff is.
I don't know about slab stuff, my obs is on timber posts with the pier coming up through the floor. Houghy did a massive pour, ask him.
Hire a digger. I dug my pier footing by hand, and my post holes, damn near killed me.
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Old 13-04-2019, 03:14 PM
benklerk
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Hi Glen

Its sandstone and clay underneath me, but its starts about 600mm underneath.

Im doing concrete
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Old 15-04-2019, 10:10 AM
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If you can get to rock (any large rock even a large floater but bed rock much better) why not do so.
The one I did at the old place saw getting to bed rock about a meter down..I then cut into it to a depth of about 2 inches.
I placed my pvc pier pipe on that base with some holes in it and placed I think 3star pickets inside..I may have had some wire netting but I am not sure...filled the pipe with concrete with some over the rock floor...I cant recall but wire tieing the star pickets would be a good idea and certainly some stainless steel mess as well...I did not but filling the hole with rock and concrete would be good...if you are going to do it go for overkill☺
Good luck with your project.
Alex
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Old 15-04-2019, 10:41 AM
glend (Glen)
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When i was building mine i ran across a thread on CN where a guy in Arizona built his footing and pier on rock. He just scrapped the dirt off and used a hammer drill to bore some holes at various angles into the rock, stuck some rebar into the holes and boxed up a footing form around it, and poured into that.
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Old 15-04-2019, 11:07 AM
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Quote:
Originally Posted by glend View Post
When i was building mine i ran across a thread on CN where a guy in Arizona built his footing and pier on rock. He just scrapped the dirt off and used a hammer drill to bore some holes at various angles into the rock, stuck some rebar into the holes and boxed up a footing form around it, and poured into that.
That, plus some Chemset on the rebar... I can't imagine a home job getting any better than that.
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Old 16-04-2019, 10:55 AM
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In any event one needs the appropriate software to remove vibration in images similar to LIGO ☺ together with gyro scopes on the pier ...
Alex
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Old 21-04-2019, 09:04 PM
Sunfish (Ray)
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Yep. On a flat site: Hire an mini excavator / two person drill to drill four 350/ 400 holes to refusal. Fill with concrete to 350 below floor level with starter bars. Join with excavated footings . Fully Reinforce and pour slab and footings in one piece. Chemset steel pier to slab. Easier if you know how deep required before you start. So drill / dig a test pit first and/ or ask an engineer for a site classification.
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Old 21-04-2019, 09:19 PM
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Quote:
Originally Posted by benklerk View Post
Just need some help and advice.

I'm planning on putting in a 3m x 3m shed to house a GSO 14" RC with either a mesu 200 mount or a JTW mount.

Anyway, Im going with a slab.
  • Slab first or pier first
  • How deep to I go with the pier
  • How high do I make the pier
  • What is a good size diameter for the pier
  • How much of a gap do I leave from pier and slab
Do the pier first - that's the important part. The slab can be poured later with a gap sufficient that the two are not touching - it doesn't have to be large. I left about 15 mm between the concrete pier and the concrete floor of my obs, and filled it with a strip of foam from Clark Rubber.

The pier needs to be 'rock' solid, so your particular circumstances will dictate how deep you need to go. I poured mine in a Formatube cardboard pipe, which is made for the purpose. I dug a 2 cubic metre hole, put in plenty of reo and and had the reo continue up through the tube for the concrete pier. Metal piers are very popular and work well, provided that they are stiff enough. Stiffness comes primarily from the pier diameter, not the material thickness. I used some 6 x 275 mm dia pipe that was readily available. Plenty of others have used smaller diameters, sometimes using tapered gusset plates to provide additional stiffness and also to avoid the pier having a strong resonance at a particular frequency.

The height of the pier needs to be calculated for your particular circumstances, as it depends on your scope, mount, and wall height for a RoR observatory. You need to do some sketches to show how how low and how high the eye piece (or camera) will be over the full range of telescope positions that you will be using.

Good luck with your project!
Chris
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Old 22-04-2019, 09:25 AM
I.C.D (Ian)
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Quote:
Originally Posted by benklerk View Post
Just need some help and advice.

I'm planning on putting in a 3m x 3m shed to house a GSO 14" RC with either a mesu 200 mount or a JTW mount.

Anyway, Im going with a slab.
  • Slab first or pier first
  • How deep to I go with the pier
  • How high do I make the pier
  • What is a good size diameter for the pier
  • How much of a gap do I leave from pier and slab
Hi Have you had look at these it will save you from digging a hole and buying a lot of concrete an reo,andit is equal to a cubic meter of concrete and if you ever move you can retrieve it and take with you Ianhttp://www.surefootfootings.com.au/
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