Best permanent pier ?

[Ian Robinson]

OK , been doing some head scratching and checking out what I have stashed in my garage rafters.

I've a couple of lengths of plastic pipe : (2m about 6" in OD and a 1.5m of 8" OD , left overs from other projects).

Now either of these would be OK as molds for making a reinforced concrete peir.

But is a concrete peir the best way to go ?

Is a steel peir better than a concrete one ? (one advantage I see straight away is that it can be moved or relocated if you move and it it bolted to a suitable concrete slab or concrete footing , but it will work out more expensive building - need someone to do the welding of top and bottom flanges and reinforcing gussetting for me.)

[gbeal]

Ian,
I'll kick this off.
I used a section of 6" steel pipe, and to this welded a flat that allows me to bolt/unbolt it from the lump of concrete that is in the ground. I don't do this as a matter of course, but I figured it would future-proof the idea. Mine is only about 600mm tall though, built for a newt.
Catch of this is that I also have another section, same pipe, and on a three legged wheelie thing, so in effect a "rolling pier", and the mount is swappable between the two. Of late I am using only the rolling job, as it is a matter of rolling it out, winding down the "feet" and attaching the 240 volt. It is as close to the pole as it needs to be (although while the moon is about I will fine-tune this a little), and with the refractor/guide-scope attached rolls easily.
I voted steel, but can see no reason why the plastic filled with concrete wouldn't do the job either.
Gary

[Gama]

You will be better off filling the pier with Cement Sand..
The sand will absorb near everything. Concrete will still allow vibrations because it is a solid, and so will pass vibrations across its volume.
Sand, will absorb it, as it moves around and stops it from reaching the other side..

Theo.

[mrsnipey]

I never thought of using sand in a pier.
Interesting idea.

[pmrid]

That's a really interesting idea. I'm just doing the footings for a slab for a roll-off and have finished preparing the pier hole etc ready for the next step. Because I am sited on shallow soil over tough rock I can't get my holes down more than about 400mm so I have built a 400 x 400 x 400 cube that will be an above-slab extension of the concrete below giving me all up about 800mm of concrete as a base. The pier itself will be some 1400 mm of 8" steel bore casing (as in artesian water bore) I have left over; I had planned to backfill it with concrete at the same time as doing the rest of the concreting for the pier base etc. But now you have made a perfectly plausible case for sand and I'd be really interested to hear what others think of it.

Peter

[Shawn]

I filled mine with sand and yes it made a difference, although I feel that it was the sheer weight of it that did the trick, also keeps the thermal characteristics of any pier more stable..slower to move off Polar in large temperature differentials.. When it was cold in the obs the pier was still warm. It can only be good, to stabilize vibration and thermal activity, yeah fill here with sand, but not off the beach salt will rust in time... :)

[Ian Robinson]

Beach sand would useable and "safe" if you give the sand a couple of good soaks in tap water in a big bucket , tipping out over a heshan screen and allowing it to drain well between each wash. 3 or 4 washes would probably remove nearly all the salt.

Sea salt is extremely soluble in water and any salt left in sand will rapidly leach out with each wash.

Beach sand is free , other sands are not.

Looks like opinion is equally divided .... so ..... I guess I'll make one pier from concrete next to the north side of my garage (have a sliding door there and will eventually put a deck there and enclose it with a slide off roof observing shack attached to side of the garage) , and one from a steel tube that wll be bolted to concrete footings about 10 m west of the other pier.
Wish I was still with Onesteel , I could have had the fabrication work all done inhouse as a "foreign order" for some tinnies.

Now just to source my a 6" OD steel tube (galvanised probably) , and a few blank flanges , some scrap reo (for reinforcing the concrete peir) , and someone to do my welding (never learnt how and not a big enough job to warant learning or hiring a welder) and a little lathework (he may as well make my mirror cell slide clips too).

[rogerco]

If anyone in Sydney Australlia is interested I got my brother to weld up a steel pier for me, he can supply the steel and is looking for the work. I am very pleased with mine at a big saving over a shop one.

Roger

[Ian Robinson]

Will keep that in mind .

I have been considering getting the local muffler guy to do my welding .

[Big Dave]

I must have cheated, I went a Pier-tech electric lift from the States and just bolted it down. You need to add extruded aliminium (or illuminum) to your pole!

Side note:
I think I may have been ripped - someone please confirm if there is a similar unit made locally in Australia? I herd rumors at issac08.....

[tempestwizz]

I went to the local re-cycling place and got some slow-combustion heater flue tubing to use as a former. I dug a hole as deep as I could - approx 1 metre square by 900mm deep. Whacked in a number of star pickets at angles into the clay at the bottom. Welded and wire-tied other star-pickets that run up through the former. On the top of each of the 4 (vertical) star pickets, I welded 3/4" threaded rod that protrudes through the top of the former.
Filled the hole and former tube with hand-mixed concrete in one exercise. Works a treat. About $50 for star pickets $5 for the former, and $50 for concrete. Absolutely solid!
Later laid observatory slab around the pier.

Couple of pics pre, and during obs construction (with home-made LX90 wedge)

BC

[Bassnut]

Ian, as mentioned elswhere, sheesh, make yourself a simple concrete pier (no reo), and spend spare cash elsewhere.

[Ian Robinson]

Looks good.

[h0ughy]

lol i bought two from sothern cross piers probably for about half of your one, the rumours are true;)

[Big Dave]

Are they still around, the web site looks to be down?

[astro_nutt]

Hi all,
I built an in-ground concrete pier for my 10" dob and mount...(as the obersvatory is a roll-away type.)
I dug a hole 500mm deep, square in shape...I then cast 3 x 150mm by 800mm concrete pins (using PVC pipe)..which were set in the hole leaving 300mm above ground...the first concrete pour was to ground level and allowed to set overnight..a equalaterial triangular shaped mould was placed over the square...(this would allow me to cast the 3 recesses into the top using polystyrene for the mount's feet after the pour)...all the concrete used had a water barrier additive mixed in.
The ground surrounding the pier had been levelled and packed with builder's sand and concrete pavers laid on top..a 300mm wide x 100mm deep area surrounding the pier at ground level also had sand packed...all viewing chairs have had rubber leg caps fitted so far no noticable vibration viewing at high magnification..works for me!!
Cheers!

[Terry B]

Mine is a cast iron modified birdbath plinth. Much prettier than all you guys ones.:lol::lol::lol:
It is very stable with 6 long dyna bolts holding it down. The top is just an EQ6 pier extension.

[Hagar]

Does this look familliar Dave

http://www.darkskyau.com/cm/displayimage.php?album=11&pos=3
http://www.darkskyau.com/cm/displayimage.php?album=11&pos=4

http://www.deskline.linak.com/Products/?id3=120

[h0ughy]

well that is drop dead gorgeous - and i have two of them to install. hey Doug since you have installed i how is the pointing accuracy and the SCP drift when going up and down?

[Hagar]

Hi David, The pier itself is very well made and quite stable accross the wide axis. The unit does suffer from quite a bit of side ways movement if knocked or bumped but I have done a little work by propping the two sides with steel tube and this stabalises it quite a bit. I have found that as long as the telescopes and mount is balanced correctly there appears to be no movement in image frames to 30 minutes.

As for SCP drift when raising or lowering, yes there is a small change but it is negligable and still allows the G11 to be very close to target in all positions.

I use this mount to allow me to lower the telescopes well below the roof of my ROR Obs and also to get above the walls. It works a treat and was the best buy I have made for my Obs.

I purchased it from Linak in Melbourne about 6 months back after finding a German site where the Piertech and this DL2 were examined and dismantled completely as a comparison. Guess what they were both the same.
Purchase price was $420 + GST. Linak had several in stock and wanted to move then so they were to be sold very cheaply.

[wysiwyg]

Here is my obs permanent pier that I constructed nearly a year ago now, with some help I should say!

I used 220 mm OD with 1 inch wall thickness and 1.7m high.
The pier was placed on a cubic meter of concrete with a 12 mm base plate.
A mount adapter plate with 3 support bolts was also fabricated using aluminium for the support plate and saddle plate and S/steel and bronze aluminium for the support bolts with 1mm thread.

Here are some pics:

Wizzy!

[Hagar]

That is one hell of a mean looking pier and mount assembly. Looks like it could withstand a nuclear attack.LOL The workmanship looks quite a bit above the standard backyard mount. Beautiful job.

[h0ughy]

don't happen to have that comparison link around do you?

[Hagar]

Here is the link, It took me a while to find it again.

http://www.dd1us.de/Downloads/A%20telescopic%20column%20as%20a%20 pier%20for%20your%20telescope%200v4 .pdf

[h0ughy]

thanks Doug - I will read that tomorrow:thumbsup:

[Lee]

With steel and portability - the pier itself is certainly portable. But to remount the thing properly you will need to re-pour another heavy slab on which to mount it..... for a little extra effort you may as well just pour another pier too. I think concrete will always be more stable (if well built) too.

[AlexN]

Terry... Get a sealed reservoir for the SBIG water cooling system... and if need be install a radiator (car heater cores work well) with a 120mm computer fan to lower the temp...

Having an open bucket of water under and around all that EXPENSIVE electrical gear would scare the living hell out of me (And I've watercooled 8000 worth of computer)

[bmitchell82]

Im not sure if this has been said before,

having reinforced concrete block for something like 32mpa in the ground .5 x .5 x 1.0 meter block, followed by leaving 20cm below surface level, and have reo bar coming though from the bottom block. also having threaded rod coming from the bottom concrete block right upto the top of the peir, to tie it all in.

Further more lay a set of bolts into the concrete before finishing it off to mount the Metal peir tube to your liking and somthing like 6mm thick walls to the lower block

Once dryed and tightened up, pour the top 20cm of the block to seal in the peir tube. Once dry fill the peir with fine washed sand and compact, leaving a 20- 30 cm void in which to cap the peir off with 32mpa concrete. all in all it is overkill but hey why do we build a peir.! the idea was from this thred utilizing the sand to suppress vibrations.

Sometimes my ideas seem and look a little bit messy, though in my head they are pristine! :D if anybody wants the plans, ill shoot something up in CAD

Brendan

[mozzie]

yes ian i have a concrete pier for my lx 90 it doesnt move made a timber frame predrilled starter barsinto concrete i ran a condute through the frame and out the bottom have power to side of pier poured concrete pulled timber frame out when dry51095

51096 :thumbsup::thumbsup:
hope this helps mozz

[sheeny]

Interesting question, to which there's only one answer in my mind... it depends.

A concrete pier can be a liability when you go to move. Oddly enough not all people are astronomers so a beautiful sturdy concrete pier in the middle of the yard may not be a strong selling point... but a steel one you can at least unbolt and take with you and leave the concrete footing largely hidden underground:P.

The stiffness of a pier is proportional to the 4th power of the diameter. I just ran some numbers to compare steel and concrete;)... For the same diameter pier a steel pier will be 10 times stiffer than the same diameter concrete one!:eyepop: (assuming 20 MPa concrete and neglecting the effect of reo). That's a much bigger difference than I expected. Since the Elastic Modulus of concrete changes with strength, making the pier out of 50MPa concrete reduces the difference to a bit over 6 times stiffer for steel.

So one might think the obvious answer to the original question is that steel is better. Well, only if you do it right!:thumbsup: I've seen a lot of bad practices in the construction of steel piers.

Some tips for constructing steel piers:

Go for the biggest diameter hollow section you can for the pier column. (not so big it fouls your OTA though;)).
Don't use a section that is not a complete hollow section e.g. no channels, I beams, angles, etc. Only a continuous hollow section will give the torsional stiffness required. (there's negligible advantage in going completely solid).
Minimise the width of both the bottom and top flanges! Too many piers I've seen have wide flanges from thin plate which become very flexible. Keep the flange plates reasonably thick and the width of the flanges to a minimum.
Minimise the height of the pier. The stiffness is inversely proportional to the cube of the height.
Grout the bottom of the pier to the footing. A lot of piers are installed without grout. This makes the bolts effectively a hinge at the bottom of your pier.
Keep adjusting bolts at the top of the pier short and thick. Again they are another flexible point.Unless you do all these things with a steel pier, I would say a concrete one is better IMHO.

Al.

[robgreaves]

Steel piers win hands down, both in rigidity and move-ability when you inevitably up sticks.

When we moved from the UK, I brought my pier with us! It's a 10" thickwalled pier with 1/2" steel plates top and bottom. I had to leave my 3ft x 3ft x 3ft concrete footing for it buried in the ground though. I can imagine the new owners striking it with a shovel one day, and thinking "what's this?" - exposing a bit of it and giving it a pull :lol:

I think the reason concrete piers are winning in the poll is they're easier to come by/make, and cheaper. Not better...

Regards,
Rob.

[Ian Robinson]

They'll probably think there's a bomb shelter there .... or an medieval or roman ruin.:rofl:

[Ian Robinson]

Hadn't run the numbers - too lazy to do the structural analysis.

Very interesting .... I might just be starting lean back towards a steel pier (for the Atlux anyway). I might be able to talk the local muffler guy into doing my welding for me if I do .

I've a gut feeling that if the tube is structural (thick walled Carbon Steel rather than Mild Steel) and the flanges (top and bottom are welded for a rigid (as opposed to semirigid) hold (full penetration butt welds rather than spot or tack welds (?) that lead to low rigidity and too much elasticity) and the flanges are thick enough , then gussets are not required. Been a while since I've done steel structure design and fab engg (over 10 yrs) .... do you agree ?

[sheeny]

Mild steel is fine. Its the same stiffness as carbon steel, but just won't handle the same stresses - but that's not our problem with a pier.;) (BTW Mild steel is carbon steel, too , it's just low carbon steel:P).

Full continuous welds all round are the go, but there's nothing wrong with a fillet weld for a pier either:thumbsup:. Full penetration prepared welds are only necessary for highly stressed and/or fatigue loaded components - which the pier isn't:).

If you can keep the width of the flange less than 4x (5x max) the flange thickness, you'll be fine:thumbsup:. There's no gussets on my pier.

:)

Al.

[Ian Robinson]

:thumbsup:Thanks - and I did say I was rusty on that stuff. (:whistle:OOoo , no pun intended.)

[GrampianStars]

G'day Y'all
I went for Steel 250mm sand filled
was quick to set up
apart from the 3 mt concrete footing :whistle:

[Gama]

Good choice with the sand fill.
I bet you cant even get the slightest vibration from the pier.
Totally absorbs near anything in microseconds.

Theo

[AlexN]

Mine is 7.25" diameter steel tube dynabolted to a 2 ft wide x 2 ft long x 2.5 ft deep concrete block, filled with foundry sand. All up, the pier and sand weigh in at about 200kgs, so I dare say my sub 15kg setup will ever cause it to vibrate.. I can kick the pier during an exposure and not see movement in the image...

[pmrid]

I sincerely hope that you are able to stop doing so quite soon.

Peter

[AlexN]

:) It definitely does not feel good to do it! :D However Its testament to the solidness of the pier.... if I tread heavily near the tripod legs during an exposure sometimes that was enough to cause problems... thats without touching the tripod itself! :)