top of steel pier design

[graham.hobart (Graham stevens)]

Hello all, I am having my steel tubular pier fabricated and I will be needing to submit a drawing soon for the top of the pier. I have ordered a Dans pier plate adaptor for the CGEM EQ6, which comes with three anchor bolts which are designed primarily for setting into a concrete pier.
I need a design that takes into account the three anchor bolts but also allows some movement for southern alignment. I wondered about two plates one on top of another with 20 degree bolt holes to allow movement, plates separated by about 10-15cm to allow for access to levelling/ alignment bolts.
Any one out there solved this issue with a steel pipe and a dan's pier plate?
graz

[bmitchell82 (Brendan)]

Not your exact setup, but Logan (Logiberra) has done a similar thing that allows flexibility in the future for different mount styles. very handy

[Poita (Peter)]

The EQ6 head should give you enough movement for alignment anyway I'd think.

[Zaps]

What Peter said.

Most EQ mounts don't need to be leveled and all those adjustable bolt type pier tops do is greatly reduce the rigidity of the whole system.

Just fasten the mount directly to the top of the pier with no adjustable bolts and plates or other junk in between and you ought to be good to go.

[bmitchell82 (Brendan)]

you want your pier approximately level.... if not it just induces a whole bucket load of hurt. If it was pointless to levelling your mount why would they give you room to make adjustments.? why would they specifically put bubble levels intergrated into the mount?

My eq6 can do a meridian flip and land the target almost dead on where it left it on the other side. I don't know about you but I always level my mount and then the adjustments come easy.

thats my 2c worth

[GrampianStars (Rob)]

G'day
I don't have a "Dans" adaptor
However I do have a steel pier with levelling plate
I use 4 x 20mm SS threaded rod and adjustment nuts.
the top plate is threaded for a flush fit.
"There is NO Flex with this setup"

[Moon (James)]

why would they specifically put bubble levels intergrated into the mount?

The only reason I can think of is repeatability - it gives you a similar starting point each night.
Levelness is not necessary for polar alignment. Especially in an observatory.
James

[Zaps]

Originally Posted by GrampianStars

"There is NO Flex with this setup"

Ask an engineer.

[Poita (Peter)]

Originally Posted by bmitchell82

you want your pier approximately level.... if not it just induces a whole bucket load of hurt. If it was pointless to levelling your mount why would they give you room to make adjustments.? why would they specifically put bubble levels intergrated into the mount?

My eq6 can do a meridian flip and land the target almost dead on where it left it on the other side. I don't know about you but I always level my mount and then the adjustments come easy.

thats my 2c worth

I think the level is there for a quick and easy setup for visual, get it level, do a 3 star align and the GOTO works fairly well.
In an obs, I don't think ultra-leveling is required, when you are probably going to have a multi-point solved solution happening anyway.

I'd forgo a leveling plate, it just becomes the weak point of the whole system to have this ultra-stiff ring-proof pier and then top it with air and bolts, seems nuts to me. You should be able to get it pretty damn level anyway without resorting to a plate.

But I could be way off, I often misunderstand crucial pieces of information.

[Terry B]

Originally Posted by Poita

I think the level is there for a quick and easy setup for visual, get it level, do a 3 star align and the GOTO works fairly well.
In an obs, I don't think ultra-leveling is required, when you are probably going to have a multi-point solved solution happening anyway.

I'd forgo a leveling plate, it just becomes the weak point of the whole system to have this ultra-stiff ring-proof pier and then top it with air and bolts, seems nuts to me. You should be able to get it pretty damn level anyway without resorting to a plate.

But I could be way off, I often misunderstand crucial pieces of information.

This is correct. The bubble level is for portable setups.
Visualise a pole going through the polar axis whilst it is aiming at the celestial pole. You can move or tilt the base to any angle and not affect the polar axis.
Having the base reasonably level just helps with balancing the scope when you are initially setting it up but nothing else.

[rally]

Graham,

How about three semicircular slotted holes instead of three threaded bolt holes

Just put a hole in the side of the pier so you can squeeze in a spanner in to hold the nuts
Or make the base plate more adjustable to it can rotate about the mounting bolts with either slots or simply large holes (probably easier to manage)

Or align your mount before attaching the pier to the ground, so the Az adjustment range is within the mounts capability.

Rally

[bmitchell82 (Brendan)]

Okay. everybody is going on about the rat cage again......... Miss understanding and lack of knowledge aparently leads to gospil and arm chair experts or arm chair engineers . Look at the individual parts.

if your going to support your top plate with 16mm threaded rod, you can expect it to flex... but if your smart and put decent size aka M20-M24 you are loading these in compression and tension not so much bending. The reason why this occurs is due to the leaver arm, the bolts are resisting any moment induced by eccentric loading in a push pull, tension compression action.

if your going to put it 200mm away from the top of the pier you can expect it to flex but if your smart and keep it down around 80-100mm when you look at the bolts they have 2 bolts which make that M20-M24 bolt more like 30 or 40mm in diameter with the M20-M24 bolt spanning 40mm.

If you want an idea of the forces to start getting movement ill do a little sum for you

with M20 Grade 8.8 structural bolts
Phi Ntf = 163kN (Phi is 0.7* for the capacity its a statistical thing to assure that you will get 163kN)
assume your bolts are 300mm in seperation
two bolts resisting assuming there are 4 bolts in total

Moment = 163*2*.3
Moment = 97.8kN-m

what load does that relate to?
force* leaver arm = Moment
lets assume your mounts at maximum of say 500mm above
with simple rearrangement or algebra we get
97.8 = .5*2*x ----> 97.8/(2*.5)----> 97.8kN

97.8kN is required to reach the capacity of the bolts now to relate this force to something we are more intune to. 10kN=1ton=1000kg so you have 9.8ton approximately........... are you starting to feel what im saying here? 9800kg it will take to start making these bolts come to their statistical maximim loading! Do remember thats 9800kgs at perpendicular to the piers axis.

if you have a mount that is capable of 100kgs thats a big mount! if you have 300kgs of equipment on your pier that relates to 3.2% capacity.. but its in the wrong direction its concentric with the piers axis not at a perpendicular axis to the pier. Pier flexure is more often than not user error and the mis understanding of how to assemble and construct.

(dont get me started on concrete and reo.....)

Unless your running 20-30" type mirrors you will not get the amount of force that is required to start making the bolts i have just told you of to go into bending. Your equipment should be balanced. If it wasn't you wouldn't be able to make your adjustments as there would be significant weight on the actual adjustments. So the load is virutally concentric though the middle of your mount head. the bolts are in compression.

remember steel is strong far stronger than you think or generally can comprehend.

Peter I am with you that you shouldn't need to get a barcode staff and a total station to make sure that your tripod is level, thats just silly, but to say that levelling your mount head out doesn't matter well you can sit there and spend ages getting your polar alignment done while ill be done in a matter of minutes with ease just because i spent a few minutes getting the level approximately right!

if your good with concreting and the like you can run your levelling at the bottom with your bolts and what not and then put in a high strength non shrink grout just like they do for every big building with steel columns. they put a little set down and have the bolts protruding. put the column down level it out, then grout. this will be the best possible way you could go about it..... It isn't hard and allows you fine adjustment before you finish up.

I may be wrong but from experience every time i spent that extra minute setting up the tripod it paid in spades after, with my POS eq6 i can meridian flip to the accuracy of 2-3 minutes of arc at 1200mm FL and a FOV of 38" by 54" that isn't bad. Also I have no T point or Maxpoint software for mount modelling and I am 99% doing photography.

Thats my thoughts on the situation and although I am not a engineer with 30+ years of experience I am a consulting structural engineer.

I hope that clears up some big miss information that is rolling around.

BM

[Zaps]

Originally Posted by bmitchell82

Okay. everybody is going on about the rat cage again......... Miss understanding and lack of knowledge aparently leads to gospil and arm chair experts or arm chair engineers . Look at the individual parts.

We are looking at the individual parts, and you ought to step back and see how those accusations apply to you.

And I hate to say it...

I may be wrong...

...But you are indeed wrong. The big issue with these setups is not deflection but vibration. These Rube Goldberg "rat cages" totally undermine all that's good about a well engineered pier.

The thing of it is that just because everyone is doing it doesn't make it right, and everyone is doing it because everyone else is doing it, and they're all doing it because some armchair engineers are telling them it's the right thing to do, when in fact it is the wrong thing to be doing.

[bmitchell82 (Brendan)]

Where is your massive vibrations coming from? please tell me? Static displacement is your vibration as there is not a dynamic load that will come up to the natural frequency of the pier.....

Oh and your I may be wrong was implying to mount levelling!

[bmitchell82 (Brendan)]

Further to massive vibrations, your mount has back lash if your system actually generated enough dynamic or sinusoidal action like that of foot fall on a large concrete plate enough to make it "vibrate" it would affect your system irrispective of if you had a 1x1m titanium pier...

Further more to this if there was that much "vibration" then how the hell do us mear mortals that rely on a set up every time with a tripod get away with the images we do.... Mike sidonio sure as hell doesn't have a bolted down pier...... Neither do I and i can show you alot of photos taken on a pier i design and built that runs a RC... its clear of the ground by a long way on bolts..... it doesn't suffer from vibration. The only time you might even take a punt at figuring something else out is if your running at the F15+ focal length.... how many scopes you see around that people are using at that F ratio

unless you can quantitively show me your vibration apart from the old hammer on the side test which means nothing because it doesn't happen then I stick by what i say!

[Zaps]

So you dig a big hole in the ground and fill it with a ton or two of cement. Maybe you form a pier at the same time or maybe you bolt on a substantial steel pier. Then you top it off with three or four relatively skinny bolts and a couple of plates of steel.

Why?

Equatorial mounts do not need to be fastened to adjustable plates for the purpose of leveling. They really don't. Honest. Equatorial mounts do not need to be leveled. Not when they're on a tripod in the field or on a pier in an observatory.

All a person has done is massively compromise the integrity of their system. That's all. And they've done it because other people do it, none of them understanding exactly why they are doing it but only because they've heard it's the way it should be done.

Equatorial mounts do not need to be leveled, therefore they do not need to be fastened to freaky plate-n-bolt contraptions slapped onto an otherwise good pier simply because they saw a few pictures on some guy's website. Some guy who doesn't understand a darn thing about the mechanics of it all.

[bmitchell82 (Brendan)]

Im not asking you about some guys website with some guys pictures in somebody elses back yard

Zaps what I am asking you is this simple...

Where are you getting vibrations from and how are you quantifying these numbers?

because you where damn quick to shoot me down with something you obviously don't know about. And if you do. well....

your comment

...But you are indeed wrong. The big issue with these setups is not deflection but vibration. These Rube Goldberg "rat cages" totally undermine all that's good about a well engineered pier.

Clearly shows that

I have designed and built a few piers now and none of them exhibit what you are saying.

A lot of people around keep on quoting gospil with out knowing fundamentals of material geometry and mechanics. I don't expect everybody to have this knowledge but I havn't spent this amount of time at uni and in the real world (no im not 21.....) and working for a company that is renowned for one off jobs and specialist structrual engineering on a world wide setting.

Oh... and you saying that your equatorial mount doesn't need to be leveled Take a test. put it on a 30 deg tilt in EW and NS and tell me how long it takes you to polar align... and how accurate it is. That would be great to see!

PS. In regards to your 1 or 2 ton of cement. you ask anybody my advice that i have given..... massive pier footings unless your running a huge setup thats going up a story or so is nothing more than wow factor..... The soil will move a 10ton pier just as fast as a 400kg pier That is the truth! Passive earth pressures are pretty funky things and for a pier to actually "twist" you need to fail the soil... good luck on that too in our situation!

[bmitchell82 (Brendan)]

Sorry Graham for hijacking your thread. mods if you want me to take it outside so to speak let me know.

[Poita (Peter)]

Originally Posted by bmitchell82

remember steel is strong far stronger than you think or generally can comprehend.

Peter I am with you that you shouldn't need to get a barcode staff and a total station to make sure that your tripod is level, thats just silly, but to say that levelling your mount head out doesn't matter well you can sit there and spend ages getting your polar alignment done while ill be done in a matter of minutes with ease just because i spent a few minutes getting the level approximately right!

if your good with concreting and the like you can run your levelling at the bottom with your bolts and what not and then put in a high strength non shrink grout just like they do for every big building with steel columns. they put a little set down and have the bolts protruding. put the column down level it out, then grout. this will be the best possible way you could go about it..... It isn't hard and allows you fine adjustment before you finish up.

This is really my point, why complicate a pier design, with a clunky solution of a plate on bolts, when you could just level the pier in the first place, much in the way Brendan describes.

If you are pretty close to level, you will have no issues, will have a stiffer pier design that will cost less money and be easier to build.

That to me just makes sense, why create an extra piece and add complexity to solve a problem you don't need to have?

As for the cage being less stiff, moresusceptible to ringing or damping down slower, I haven't tested it to know, but it is extra complication and cost and potential fail point that can be avoided. Why go to the trouble of adding it?

I would be making my pier as level as possible, and aligning it north south as closely as possible (solar noon method is more than accurate enough) and then any micro adjustments needed after that can happen within the mount head itself.

Simple, solid and straightforward.

[Terry B]

Brendan
I agree with you about the hype on this subject. I just feel the top of the pier needs to eyeball level to balance the mount on when you first attach it. Not perfectly level. It will also never need adjusting. If the entire pier moves with soil movement etc you would adjust the alt adjustment on the mount rather than the top of the pier.