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 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!
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.
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.
don't happen to have that comparison link around do you?
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.
Mine is a cast iron modified birdbath plinth. Much prettier than all you guys ones.
It is very stable with 6 long dyna bolts holding it down. The top is just an EQ6 pier extension.
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)
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! if anybody wants the plans, ill shoot something up in CAD
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 dry
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.
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! (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! 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.
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
I think the reason concrete piers are winning in the poll is they're easier to come by/make, and cheaper. Not better...
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
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.
They'll probably think there's a bomb shelter there .... or an medieval or roman ruin.
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.
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! (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! 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.
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 ?
Last edited by Ian Robinson; 10-12-2008 at 04:22 PM.
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 ?
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).
Full continuous welds all round are the go, but there's nothing wrong with a fillet weld for a pier either. 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. There's no gussets on my pier.
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).
Full continuous welds all round are the go, but there's nothing wrong with a fillet weld for a pier either. 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. There's no gussets on my pier.
Al.
Thanks - and I did say I was rusty on that stuff. (OOoo , no pun intended.)
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...
It definitely does not feel good to do it! 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!
if anybody wants the plans, ill shoot something up in CAD
.
... For the same diameter pier a steel pier will be 10 times stiffer than the same diameter concrete one!
(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.
.
OOoo , no pun intended.)
