Pier Diameter

[Andre27]

Good Day To All

For those that have practical experience with DIY piers ,the following question.

Would a 2300mm (9.2inch) steel pipe at a lenth of 1.2 m (48 inch) used as a pier be stable enough for astrophotography with 8 - 10 Inch reflector and EQ6 mount. (wall thickness 8mm)

It is assumed that the pier is to be bolted to a concrete base.

I have an offering for the pipe at a very good price and need to know asap.

Thank you

Andre

[strongmanmike]

Sounds perfect to me Andre :thumbsup:

Weld on a good thick base and four long gussets (base mounting holes next to the gussets) and it should be excellent

Mike

[rally]

Andre,

This is ideal.

The angular deflection for a nominal load (eg torque load of mount, wind, cable drag, imbalance etc) will result in less than one arc second

In your case its actually under 0.5 arc secs - and is what I would consider perfect, even for imaging with image scales under 0.5 arcsecs per pixel with top end equipment.

There is no need for any gussets on this pier as your rigidity is already within ideal levels, but having a base plate of 10-12mm thickness to bolt it to the ground would be a good finish to transfer that rigidity to the ground.

Good luck with your imaging

Rally

[Wavytone]

The place it will flex is the plate and the bolts to whatever is below. Not the pipe.

[leon]

Perfect indeed, and if you want some overkill, just fill the bolted pier with concrete, it will never move.

Leon

[Astroman]

As others have said it will be ideal, need a good base, gussets and your away.. I used to have a pier for my EQ6, scope looked huge on top of it.

[Wavytone]

Regarding filling with concrete... Consider how you or someone else is going to dispose of this one day, you could be creating an expensive problem.

[AstroJunk]

Your going to run into serious tube strike issues near the meridian with that width of pier. I've just had to have a skinny pier built for my EQ8 because my existing 10" one was way too restrictive.

And BTW, my 5", 1.3m pier carries nearly 100kg of kit and there are no flexure issues. (I didn't say there is no flexure, what ever there maybe is accommodated for by pointing algorithms and guiding).

[Meru]

Sorry to hijack but out of curiosity, if a pipe of that diameter is suitable, what about a square section? I ask because I have access to a 125mm square section with a wall thickness of 9mm, and a 150mm square section with 6mm thickness (Both are approx 1m high). I wanted to use these as the pier, and then weld it to a 300mmx300mm 16mm steel base plate.

I suppose the vertices of the RHS sections would have some stress concentration but I dont see why it would matter, given that the loads arn't exactly massive. Thoughts on this?

[el_draco]

Just don't whack a rat cage on top if you can avoid it. Negates the rigidity of the pier.

[troypiggo]

150x6SHS has the bigger Ix and Ze, so is stiffer and stronger than the 125x9SHS. Whether they're suitable for your mount and scope depends on what you're putting on them.

Note that neither of those come close to the stiffness of a 230x8 (or thereabouts) CHS. However a 150x6SHS is stiffer than a 150x6CHS.

And totally agree with the above, do not put one of those ridiculous rat cages on top. Will only weaken the system.

[Meru]

Hi Rom,
For a while I thought you were just making a joke about literally a rat cage - then I read up on it and now feel like a noob :P Yes I would ideally like to stay away from that design if I can, don't like the idea of everything sitting on 4 M20 bolts or the like. I'm going to start a thread soon on my pier build and I'm leaning towards having small grub screws/shims for fine adjustment at the base.

Troy,
You made me dig through my Uni books again :P I'd be mounting a NEQ6 + RC8, conservatively estimating 50Kgs to be the absolute highest I'd ever go. I figured it wouldn't be as stiff as the 230mm CHS but it will definitely do the trick for me. And based on people's opinion so far, I will probably have no rat cage at all :)

[AstroJunk]

The need for a level pier or base is often overstated. Of course, you will lay your foundation pretty level and when you dynabolt the pier down it will be true to a couple of degrees or better anyway.

That's good enough.

When you do a polar align, the errors are removed naturally by adjusting the mount itself to ensure that the polar axis is pointing in the right direction regardless of how flat the base is. Magic!

[Meru]

That is my main concern with this design, that if the concrete isnt damn near perfect level then it'd be a PITA to setup!! But now that you mention it that actually makes sense; any tilt back or forth will be taken into account by the latitude adjustment, any tilt sideways wont matter as it'll be along the axis for RA and you can adjust the rotation of the mount for finding the polar axis. Excellent :D

[troypiggo]

When detailing column bases in structures, there are 3 typical ways of doing it.

1. Cast the column into the footing. You get the rigidity at the base, but you need to ensure the column is vertical during the concrete pour. Not much construction tolerance. This is important if you're doing a 6m high structural column, lightpole or something where it's visible to everyone and if it's excessively out of vertical, people will notice. A 1m high mount pier that only you will see is not so critical. Strength is often fine, it's visual perception of the out of vertical

2. Cast into the footing a bolt cage, and have a baseplate on the column. Put levelling nuts under the baseplate so you can level the column, then non-shrink grout under the baseplate. This gives much tolerance in case the footing pour knocks things out of whack a little. Baseplate thickness and connection to column needs to be sufficient to take the base moment.

3. Same as 2 but use chemical anchors like Ramset Chemsets. More forgiving on the bolt location (ie they can't get knocked during concrete pour), but not as strong as cast-in hold-down bolts. Not to say they won't have enough capacity for a mount pier, just that for structures like portal frame buildings etc where the tension in the bolts is much higher, we prefer cast-in bolts.

All are viable options for the sort of loads, eccentricities, alignments etc tolerable by EQ mounts.

[Meru]

Spot on Troy,

That is a very good summary and at the moment I'm leaning towards option 1 or 2. I am confident I can get the concrete very level so probably go option 1, saves the added complexity of option 2. I think it is time I started a new thread

[Andre27]

Hi All

The construction of the pier has commenced , I am making a copy of my Eq6 adapter to bolt to the top plate as the total cost for the adapter is less than R 30.00 (AUD 3) from scrap metal.

I decided on 310 mm 8mm wall thickness pipe at 1m pier height with 16mm base plate and 12mm top plates.

I need to construct two piers , I am using the rats cage construction on this one , I would like to see for myself how this will effect the performance of the mount with regard to astrophotography , if need be I can always change the design later , I have run out of time and need to complete this project before all the engineering shops close for the festive season.
Wish me luck

[Meru]

That's dirt cheap, hopefully the full set up won't cost you too much! 16mm base & 12mm adapter sounds good to me. As previously mentioned, be careful with the 12mm when welding as it may warp. We'd all be curious to see how your rat cage set up compares to the straight-up all welded approach if you choose to go that path with the second pier.

Best of luck for getting it finished for NYE!

[Andre27]

Hi All

Unfortunately the Engineering shop closed for the holidays before they finished cutting the gussets , so I now have to wait until the end of Jan 2014 before continuing with this project :(

[I.C.D]

Andre,
Instead of waiting to welding gusset to the tube fill it with sand , my pier is 800mmH x100mmW x 5mm T 3/4 fill with sand and I am using a EQ6 and the OTA is a Meade 8”sn
Ian C :thumbsup:

[Andre27]

Unfortunately they closed shop with my pier top plate in the shop.
Nothing to do but wait for the middle of January:sadeyes: