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  #61  
Old 19-02-2010, 02:16 AM
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Waxing_Gibbous (Peter)
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Pleas don't think I'm being fatuous. I'm not.
The best pillar combo I can think of is an old railway rail, or small 'I' beam, pounded into the ground with a fence post pounder, surrounded by formatube and filled with concrete.
Typically the rail should be driven into the ground 60/40 (60% below ground).
I rather discovered this by accident while trying to remove one.
It required a 30 tonne excavator and 400 grammes of TNT.

The advantage to this set-up is that rails / beams are practically free, the concrete required is minimal, and the end-result is almost immune from vibration short of an earthquake.
The disadvantage being one needs a fencing contractor with a tractor and post-pounder (about $80 p/h) and a bit of space for him to move around in. The bloke who removed it remarked that it would probably only cost $100 - $150 to put in but it was costing about $400 to get out.
Were the pillar not in a completely veiw-less position, I would have used it in a minute.
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  #62  
Old 19-02-2010, 01:29 PM
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Quote:
Originally Posted by troypiggo View Post
I don't know about the other guys, but I didn't take too well to your 2 comments about what rubbish you were reading. Perhaps the tone of your posts has yielded the replies they deserve.

Agree totally!
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  #63  
Old 19-02-2010, 08:52 PM
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Quote:
Originally Posted by troypiggo View Post
I don't know about the other guys, but I didn't take too well to your 2 comments about what rubbish you were reading. Perhaps the tone of your posts has yielded the replies they deserve.
"Ditto" Troypiggo.

The rubbish being referred to was with regard to the blind faith some continue to place in unproven pier deflection figures. Listen mate all I want and a lot of others is for the answers to really simple questions that is all. Don't go and get all precious on me now.

There have been simple questions asked that still go unanswered, and whenever they are asked, attract criticism and insult. Why? Thats unfair and not in the spirit of this forum.

After such a lenghty discussion and so much reliance on unsupported figures of so called pier flexure, one has a right to ask questions that reveal the full facts and should not be riduculed.

When these findings/figures are placed under simple scrutiny there is a reluctance to substantiate the figures? Why?

Feels like we are in a UN climate change meeting and Penny Wong is running it.

All I have asked is simple questions in a non offensive way and I would ask respectfully for someone to provide some answers.

If no one wants to answer them thats OK but the reluctance to address simple queries on test results only raises more scepticism on the figures quoted.

I am sure I am not the only one who challenges them.

Instead of firing bullets lets respect each others opinion, get into the nitty gritty and tease out the questions, get answers and come to a well informed outcome. How about it
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  #64  
Old 19-02-2010, 10:33 PM
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Well, hatman, this is because no-one knows for sure, or so it looks like.
Of course, one single rule applies here and that is: bigger the better, you can not miss that way.
But, unlike some others on this forum, I can not afford to spend un-necessarily huge amounts of money and effort for something that is not really needed for what i want to do as amateur astronomer... I want to spend my available resources rationally, I want the biggest possible bang for a buck and obviously I am not the only one who thinks in those terms.
After all this discussion, and based on my so far experience with piers I have build in the past, my conclusion is that *anything* fixed is better than removable tripod.
Why?
1) Because it is fixed. No need to align every time the telescope is used.
2) Also, because the mount and telescope are balanced, so there are no changing lateral loads, even during very long imaging sessions.
3) Then because we are not in positional astrometry business, where the stability of mount over plolonged time periods is paramount (and then, who would use EQ6 or even much better for this job anyway???
4) And when it is windy, it is not good to do anything anyway. No mount (except the most massive ones) could cope with this - pier will be the tiniest problem in those conditions.
5) when there are people walking around, it is show time and not imaging or measuring session.

Everything above this is just a gross overkill, un-necessary spent money and/or effort.
Well, I guess this is not the problem for people who could afford it.
But the importance of correct information is essential, still.
Because from A to B you can get in Ferrari or in Datsun 180B, in the same time, with the same effort. I would always choose Datsun 180B, and the rest I would spend on better things (even beer in good company is way better)
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  #65  
Old 19-02-2010, 11:01 PM
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troypiggo (Troy)
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It's not that nobody knows. It can be calculated providing every single dimension, weight, size, eccentricity, wind load, slew speed, founding conditons, acceptable deflection limits etc are all quoted. It can all be modelled and analysed using very simple priciples and software. The problem is noone ever provides all the information, and all of the different combinations are almost infinitely variable and consequently so are the results.
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  #66  
Old 20-02-2010, 10:08 AM
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Quote:
Originally Posted by hatman View Post
...
The rubbish being referred to was with regard to the blind faith some continue to place in unproven pier deflection figures. Listen mate all I want and a lot of others is for the answers to really simple questions that is all. Don't go and get all precious on me now.
Putting a smiley face after saying I'm precious is not really helping your cause in getting questions answered. By me, anyway.

Quote:
Originally Posted by hatman View Post
There have been simple questions asked that still go unanswered, and whenever they are asked, attract criticism and insult. Why? Thats unfair and not in the spirit of this forum.
I'd like you to cite where I criticised you and insulted you. If you're referring to someone else, was that before or after you said "what rubbish" you were reading? Do you think perhaps your tone and choice of words may have been what attracted it rather than the questions themselves?

Quote:
Originally Posted by hatman View Post
After such a lenghty discussion and so much reliance on unsupported figures of so called pier flexure, one has a right to ask questions that reveal the full facts and should not be riduculed.
All figures I quoted are fully supported by engineering principles/calculations/analysis. I said what I based those on in my posts. I have not ridiculed you.

Quote:
Originally Posted by hatman View Post
When these findings/figures are placed under simple scrutiny there is a reluctance to substantiate the figures? Why?
You are probably mistaking an inability to substantiate the figures with the motivation/incentive to do so.

Quote:
Originally Posted by hatman View Post
Feels like we are in a UN climate change meeting and Penny Wong is running it.
I find this a bizarre statement on many levels.

Quote:
Originally Posted by hatman View Post
All I have asked is simple questions in a non offensive way and I would ask respectfully for someone to provide some answers.
Sorry mate. They are not simple questions to answer because, as I've said repeatedly in nearly every post I've made in this thread, the variables contributing to pier deflection are vast and wide, and not one person, including and especially you, have provided enough to carry out a detailed analysis to be accurate to the sort of levels required for the magnitude of deflection limits being set. It would be utterly impractical to do so. You'd be better off being conservative and oversize things to take care of the things you haven't or can't allow for.

I would also dispute that you have asked the questions in a non-offensive and respectful manner.

Quote:
Originally Posted by hatman View Post
If no one wants to answer them thats OK but the reluctance to address simple queries on test results only raises more scepticism on the figures quoted.
Again - you are probably mistaking an inability to substantiate the figures with the motivation/incentive to do so.

Quote:
Originally Posted by hatman View Post
I am sure I am not the only one who challenges them.

Instead of firing bullets lets respect each others opinion, get into the nitty gritty and tease out the questions, get answers and come to a well informed outcome. How about it
I won't be firing any more bullets in your direction. By bullets, I assume you mean responses?
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  #67  
Old 20-02-2010, 10:17 AM
hatman
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Thanks guys for taking the time to respond and I appreciate genuinely your comments. A I have learned a lot from all the discussion and and hopefully have been able to provide something meaningful. Do you think the idea of a stubby holder on a pier might take off?

As a matter of interest, Is there anywhere on the IIS site where one can view images of members observatories or setups specifically or is it randomly spread throughout the different forums/site? It would be inspiring to see what others are doing with their setups, perhaps under a specific page dedicated to images of that?
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  #68  
Old 20-02-2010, 06:52 PM
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Quote:
Originally Posted by troypiggo View Post
It's not that nobody knows. It can be calculated providing every single dimension, weight, size, eccentricity, wind load, slew speed, founding conditons, acceptable deflection limits etc are all quoted. It can all be modelled and analysed using very simple priciples and software. The problem is noone ever provides all the information, and all of the different combinations are almost infinitely variable and consequently so are the results.
I do not think so..
The problem is, people do not know really what is important so they want to calculate in everything that comes to their mind, which is of course waste of time and effort.
Engineering and design in general are all about making a right compromises, to satisfy some minimal requirements for the task.
My concrete pier (16cm in diameter, concrete filled PVC tube and reinforced with 3 1 metre threaded rods) was quite adequate for my 10" reflector. True, I did not use it for imaging then, but all problems I had then were due to everything else but pier (mainly it was the way I mounted the Newtonian tube on the DEC flange, I had a weak point right there.
But for visual, it was perfect.

I plan to do it again soon in my backyard, and will certainly post my assessment of how it behaves... it will be biased report of course

Last edited by bojan; 20-02-2010 at 08:36 PM.
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  #69  
Old 21-02-2010, 07:22 AM
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My point throughout this whole thread has been that it's not worth designing the absolute smallest, most economical sized pier. It can be done, but it's not worth it. I wouldn't do it if it were my pier. And I'm a structural engineer.

I totally agree with you about eng'g and design being about making the right compromises. That's what I've been trying to say, maybe using different words, but the meaning/result is the same.
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  #70  
Old 26-02-2010, 02:09 PM
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Paul Haese
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Troy, I was just wondering if you calculate my pier defection if I supplied the information? I will understand if you don't want to, but I thought it might be good to work the numbers with an actual pier in place and working.

height: 1300mm
diameter: 200mm ID
Wall thickness: 13mm
Base plate: 12mm at 450mm diameter and flange welded
Gussets: 4x 150 base tapered to 20mm at distance of 450mm from base and welded both sides of gussets.
Top Plate: 12mm thick and welded on top of pier.
Pier support: 8m x 1m x 1.1m reinforced concrete and support bolts caged to a depth of 600mm below concrete level.

If you need any more info please let me know. I think that is everything I specified at the engineering firm.

This should be interesting to see what comes of it.
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  #71  
Old 26-02-2010, 02:25 PM
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Moon (James)
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Paul,
The CN link will give you a rough idea. In your case the closest match on the table looks like 48 inch high, 8.4 inch ID results in a 1.5 arc sec deflection if you push on it with a 5 pound force.
Bump it up to 10 inches = 0.6 arc sec
Bump it up to 12 inches = 0.0 arc sec.

Of course this is very rough, but it gives you the order of magnitude which is all you need to know when deciding how big the make the monster.

James
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  #72  
Old 26-02-2010, 02:53 PM
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G'day Paul. I've PM'd you.

Quote:
Originally Posted by Paul Haese View Post
Troy, I was just wondering if you calculate my pier defection if I supplied the information? I will understand if you don't want to, but I thought it might be good to work the numbers with an actual pier in place and working.

height: 1300mm
diameter: 200mm ID
Wall thickness: 13mm
Base plate: 12mm at 450mm diameter and flange welded
Gussets: 4x 150 base tapered to 20mm at distance of 450mm from base and welded both sides of gussets.
Top Plate: 12mm thick and welded on top of pier.
Pier support: 8m x 1m x 1.1m reinforced concrete and support bolts caged to a depth of 600mm below concrete level.

If you need any more info please let me know. I think that is everything I specified at the engineering firm.

This should be interesting to see what comes of it.
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