Scope height and pier question

[edjrgibbs]

Hi all

Looking for some advice so bear with me. A few factors still to be addressed but will likely be moving into a house soon and have permission to build a roll off obsy. I've identified a shed that could easily be adapted for the purpose http://www.tigersheds.com/product/tiger-shiplap-pent-shed/?option=46

I had a question about the Pier though. I've found these that look like decent value for money http://www.365astronomy.com/primaluce-lab-c82-pier-for-concrete-base-with-adapter-for-eq6-az-eq6-cgem.html. They are only 82cm high though and the shed is 191cm high. Even with the mount on top it would be pretty low down in the shed. Would it be possible to create a raised platform from hollow breeze blocks, rebar and cement to attach the pier to in order to raise it up to the highest possible position to allow max clearance?

Thanks
Ed

[RayD]

21 minutes ago, edjrgibbs said:

They are only 82cm high though and the shed is 191cm high

An average height is around 1m to 1.1m, but it really depends on how high you need it to be to see over your shed walls, clear everything around it when slewing, and see as far as you want to at the horizon.  Don't forget the higher you go the thicker and stronger the tube will need to be, so I suspect that's why this one is only 820 high.

Best thing to do is to start from the scope and work down and see how much higher you need to come. If you are not putting in a concrete base for the pier to bolt to then you can build up an upstand, but I wouldn't do it with breeze blocks, they're too soft, you would need at least 7n blocks (medium density) and make sure they are well bedded down as everything will have a tendency to move laterally.  Remember most installing steel piers are bolting it to 1/2 to 1 tonne of concrete, so that gives you an idea of how stable it needs to be, particularly if you are going to be imaging.

[edjrgibbs]

Ok, thanks ray, this is really helpful. I'd planned to use these https://www.travisperkins.co.uk/Hollow-Dense-Concrete-Block-7-3N-215mm/p/988088 side by side buried to 2 feet or so, built up to half a meter or so above ground, rebar in the centres and concrete poured into them and around the base. Not sure if i'm explaining myself very well...

[RayD]

27 minutes ago, edjrgibbs said:

Ok, thanks ray, this is really helpful. I'd planned to use these https://www.travisperkins.co.uk/Hollow-Dense-Concrete-Block-7-3N-215mm/p/988088 side by side buried to 2 feet or so, built up to half a meter or so above ground, rebar in the centres and concrete poured into them and around the base. Not sure if i'm explaining myself very well...

Yes I understand what you mean and those blocks are fine for that.  

I wouldn't think you'd need to build up half a metre though.  If your shed is 1.9m, the pier is 820 and the mount is say 450 or so, you shouldn't be too far away, so worth just setting your scope on your tripod and having a measure to see if you need to build up at all, and if so how much, but I'd be surprised if it was more than 200mm or so.  If you need to come up half a metre you'll need to go down a lot more than a couple of feet to make it stable.

[edjrgibbs]

Ok, makes sense. Thanks for that. Measuring tape out over the weekend. Thanks for the advice. 

[martin_h]

How are your horizons? My obs walls are about 6 feet high but that is ok for me as I'm surrounded by houses and can't see  much below 30 Deg, and, being higher they cut out wind and a lot of light pollution.

[edjrgibbs]

Pretty good north to north west as well as north east and east. House to the south though. 

[RayD]

1 hour ago, edjrgibbs said:

Pretty good north to north west as well as north east and east. House to the south though. 

Best way to do it is to do a simulated view, i.e. perhaps a scrap of wood propped at the 1.9m height you noted and see how that sits with your eye line, then measure from the minimum height you need the scope to be to obtain all you views, and then work your way down from that, deducting the height of the mount and pier, and seeing what that leaves you to make up.  I would probably get my equipment on a tripod set up on a temporary floor the same height as the shed base would be, then look through the scope with a sheet or similar propped up where the shed wall would be.  It is a bit of faffing but it could save a lot of headache.

To be honest it may even be easier to get a reciprocating saw out and chop a bit off the top of the shed than it would be to make a suitable upstand.  If you can face the shed with the pent section (lowest bit) towards your North, then you probably won't have to do too much.

[martin_h]

My concrete block extends about 18" out of the hole to raise my short(ish) pier

[laser_jock99]

A 'solution' I don't think I've seen anybody else use yet is to park the scope 'weights up - scope down'. The counter weights can be removed at the end of the session and the counter weight bar retracted into the mount.

Thus you can leave a big scope permenently mounted and still image down to the horizon!

[edjrgibbs]

Thanks for the advice guys. Another question. How do I work out how much concrete i'd need for the base?

[harry page]

Hi

1 ton of ballast will do 0.6 m3

Harry

[iapa]

qty 6 off 600mm x 600mm slabs

stacked with resin securing each layer

drill through for M12 mount bolts and use resin again to secure those.

Would that not work to install a 250mm dia steel tube pier?

[spillage]

I think that the slabs would be prone to cracking when you drill them.

If I was taking that approach I would break up a couple slabs and then use concrete in between the slabs using the bits of broken ones between each slab so you get a gap for the cement.

A bit like making lasanga.