Pier ready!

[spaceboy]

I'm happy to go with common sense on this one but also happy to be proved wrong if you feel the need ? I work with steel and you tend to pick up on what works and what dosen't but it would be ignorant of me to think I know it all so I am always humbled by other who offer their wisdom.

[shedifice]

Nce pier

Just to add my 2p

• the tube diameter length and wall thickness will determin the stiffness of the pier, ie how much it bends if loaded.
  
• Concrete in the ground will anchor the tube in the ground.
  
• Concrete in the tube will increase its mass and therefor affect the vibration and resonance of the tube.
  
• 3 screws at the top will have their own resonance but this will be probably a higher frequency to the tube.
  
• concrete in earth in the groung will be more damped than a pier bolted to a large concrete slab. I would therefor be more concerned/interested in teh vibration of a pier on a slab than in the ground.
  

All these factors are variable depending on length, mass on top etc etc. If your pier was to bend as you raised and lowered your scop it would need to be stiffer. If it vibrates when knocked or continues to vibrate after you motor it then it needs damping.

Sorry for brain dump but its the engineer in me.

I am interested in this stuff as I am shortly to make a pier myself.

L.

[Zakalwe]

I'm happy to go with common sense on this one but also happy to be proved wrong if you feel the need ? I work with steel and you tend to pick up on what works and what dosen't but it would be ignorant of me to think I know it all so I am always humbled by other who offer their wisdom.

Likewise .....I spent years in fabrication...everything from steel erecting to commercial vehicle (40 tonne trailers) fabrication.

I'm interested as I will be putting in a pier as soon as I can. I have seen varying adherents to different practices. Some of it is clearly snake-oil (such as the videos that Pulsar Optical have on YouTube), some of which is good sense. I am forming the opinion that a lot of what is talked about is lore becoming fact, but am interested in the whole subject.

[martin_h]

There is a lot talked about vibration in mounts....search the threads on here! Concrete v's steel etc. I personaly dont tap my pier with a hammer while I'm imaging so I wouldnt know if it rings or not! Granted there will be low level vibration from the motors etc but if you can detect that in a finished image good luck to you!

My pier is a steel tube bolted to a lump of concrete and, yes, the top plate is supported by 4 x 16mm threaded rods - they don't move, vibrate, or ring....or if they do I can't tell in the final image, and that afterall is the final test surely?

[spaceboy]

On another note I'd like to apologies to g0ibi for the thread hi-jack. As his pier is complete, I doubt any of what I have contributed is appropriate.

[g0ibi]

It's OK Spaceboy, no probs. An interesting read anyway!!

[nmoushon]

I know I'm still new to AP in general and have no personal experience with piers and mounts and how they effect each other but I do have a professional view of this that I think might help. (I'm an architect btw)

Just going to answer/clarify/state a couple things that I think can help:

"There is a formula some where for judging how deep a post should fix into the ground given it's height. The calculations also determine how wide the post should be to reduce any loss of strength." -Spaceboy

Correct - The length of the pier above ground should equal the length of the pier below ground. The size of the pier does matter and you can easily do the math but unless you have a seriously large scope/mount, and wallet I might add, the 6" pier he has is plenty. Guessing on size btw. You can always use a steel tube instead of pvc but that can get expensive. *Or corrugated metal tubing*

There was banter back and forth about flexing in the rods and their lengths. Both what Zakalwe and Aoraki said are correct. Your going to have a heck of a time producing flex of that rod from only 75mm away. You can do it but it's going to require a lot a weight. On the other side of that coin though all the weight of the equipment is not at 75mm away and are double and triple that distance even. Thus producing even more strain (flex) even though its the same amount of weight.

Malc is right about the resin anchors. They are great if you already have a cement slab that you want to connect your pier to. But if you're starting from scratch drilling into your concrete pier will actually weaken it giving the surface area so its better and easier to place the threaded bars into the concrete before it cures.

Where the most vibration, like most everyone has mentioned, is the connection between the pier and the mount via the bolts sticking out of the pier. Off the top of my head the easiest way would be to use more bolts. Not that it makes it more secure but that it helps transfer the vibrations from the equipment through connection and into the pier and the ground.

Disclaimer: This is just professional opinion and it's all related to architecture and thus subject to error based on personal experience by others.

[malc-c]

To be fair, I think Martin hit the nail on the head. It matters not what you make the pier from, or how you fasten it, so long as it does the job of supporting the mount and scope, enough to give you the images you want be that visual or via camera's then that's all that matters.

[Grunthos]

Rather than get into an extended esoteric debate and a detailed synopsis on structural engineering design I'll point out a good YouTube video.

Part 1 (of 2),

, by Robert Dalby (FRAS) at Astro Engineering.

It's a bit basic (I am an Engineer!) but certainly hits the right notes...

I'll certainly be consulting AE when I start serious work on an observatory.

[Gina]

I did a test when I was using my Newt and imaging. I thumped the pier hard with my hand (not quite enough to hurt myself) - no affect. I hit the top of the pier adapter - no effect. I hit the mount body - nothing. I hit the scope - some vibration but not a lot.

Later I added a mount extension as I wanted a bit more height (the SW NEQ6 version) and when I hit the mount on top of that I got a small vibration but again hitting the pier adapter top caused nothing.

In practice I have used a webcam with 2x Barlow and not experienced any problem with vibration. I was even able to focus my Newt, with a coarse R&P focuser without getting vibration problems. In reality, it's rock solid. That's good with me regardless of any theories

[Damo636]

There seems to be an awful lot of 'overkill' on piers and mountings and yet many get by on a flimsy tripod without any problems!!

"Overkill"?, i think i may fall into the overkill category with my rather industrial effort! M18 threaded bar, 6mm top plates and bolted down on top of 3/4 cubic metre of reinforced concrete!!

Nice job on the pier by the way