831 replies to this topic

[macdonjh]

joshman, having a steel pier made in sections which bolt together won't give you any benefit after it's installed and will make it more expensive.  Of course, if it's so heavy you can't get it in place to install it, then that would be benefit enough.

 

I've never done the math to see if multiple columns would provide benefit.  My initial thought is the extra complexity and fabrication costs wouldn't be worth it given the alternative of simply fabricating a pier from larger diameter and/ or greater wall thickness stock.

 

Having permanent "pads" for the feet of your ATS portable pier would give you many of the benefits of a permanent pier.  If you lay-out the locations and orientation of the pads carefully, polar alignment will be repeatable.

[speedster]

Some considerations that might help you decide:

 

In a typical pier application, deflection is independent of weight.  Deflection is the same whether the load is 30# or 300#.

 

High performance piers are necessarily heavy.  No economical way around that.  But, there are ways to safely handle a heavy pier without equipment - even with only one person.  You only have to move one end at a time.

 

Clay + water = movement.  It's nice to get below the most active surface soils but it's no crisis.  It just means you may be touching up PA every now and then. 

 

Multi-section piers can be fine if you use enough bolts in the connection so that the pieces can be considered bonded and therefore a single unit after assembly.  The down side is cost.  Each section cost about the same as a whole pier due to fabrication of additional plates.

 

Multi-piece piers can be fine but there is little weight savings for the same performance and the cost is very much higher.  Connection design is different, as well as some other things, but it can certainly be done.

The ATS tripod has a small foot radius so instead of 3 independent footings, you could enlarge the pier cap a bit and catch all 3 legs on one foundation.

 

Tripods are an excellent structural shape but we introduce problems when we make them portable.  Stiffness is sacrificed for lighter weight (aluminum is 3x more flexible than steel) and in all the hinges and connections for folding can be sources of arcsec deflection. 

 

Another option is to use the tripod since you already have it and see if it meets your needs.  Tighten all the joints or put them in a bind so that it is no longer collapsible to try to take out any wiggle.  If that works for you, you can attach the legs to the foundation with some clip angles.

 

No need to be concerned about resonance.  Everything vibrates. Even the back of your eye has a resonant frequency. A telescope pier has not one but several modal frequencies. Fundamental frequency corresponding to first modal shape is called natural frequency of the system. Increasing stiffness increases the natural frequency. Increasing the mass decreases the natural frequency. An increase in the damping diminishes the peak response but broadens the response range. What does this mean to a properly designed telescope pier? Absolutely Nothing! Since the magnitude of the vibration is less than the deflection, less than the camera can detect, it doesn’t matter if it’s vibrating at 40 Hz, 400 Hz, or 4,000 Hz.

 

 

 

 

[billywjackson]

I have a question for all the knowledgeable folks on here. Instead of putting leveling nuts under the base plate of a steel pier (like is shown in the pier 3 design earlier in this thread) is there a reason not to put the base plate directly on the concrete base? I'm assuming the top of the concrete will be level and smooth.
I'll be building a steel pier out of 4' tall 6" sch 40 pipe. I have 1/2" plate for the base and top plates. The concrete will be 4' in the ground, and as close to 12" square as it can be using a mini ex with a 13" bucket. so probably end up being closet to 14" or 16".

Thanks!
Clear Skies!
Bill

[macdonjh]

The leveling nuts under your pier's base plate can make your pier's top plate level if the concrete below is out of level, or if your pier isn't quite square. Or both.

To your point, you can still achieve polar alignnent with a "crooked" mount, but it's easier if your mount is level. It also looks better to most if everything is level and square.

Edited by macdonjh, 07 July 2024 - 11:39 AM.

[speedster]

You can certainly bolt directly to concrete for a telescope pier.  But, the surface is neither level nor flat.  It may, at first, be level enough and flat enough to meet your expectations but the surface gets displaced when you embed anchor bolts.  If you wind up with a problem, you can shim but leveling nuts with clamping nuts avoid that possibility altogether.  So, the first advantage is installation.  Another advantage is easy of leveling.  Concrete has about 1/10th the strength in tension as it has in compression and double nutting avoids the tension load of tightening the base plate against the concrete.   With the base plate raised off the concrete, you eliminate moisture hiding between steel and concrete and the potential corrosion issue there.  When the added cost of leveling nuts is insignificant, there is no reason not to go with leveling nuts and enjoy the advantages. 

 

It's fairly common to see handrails, small bollards, and some telescope piers bolted directly to concrete but larger assemblies have some definite reasons to use leveling nuts.

 

Edited by speedster, 07 July 2024 - 12:38 PM.

[Victory Pete]

I like having 3 leveling points, there is never any conflicting forces between 3 points. To level I put a small level in line with the bolt I am going to either raise or lower, then rotate 120 degrees and do another, repeat this sequence and as you go around you will see there will be minimal, if any additional adjustment needed. I have a circular bubble level but find it confusing to either level this pier, or level my camper.

 

[billywjackson]

Thank you all for your advice. Leveling nuts it is. I originally planned for four 3/4" bolts for the anchors, but may go with three, for ease of leveling.

Thanks again!
Clear Skies
Bill

[Victory Pete]

If you have control of the size of the holes, go with 1" if you can. My first pier had 3/4", this one is 1". It is very solid, I do have a thick base and 6 massive fins,which adds to the equation.

[billywjackson]

I'll have to see if I can get hold of some 1" bolts. Leveling 3 points is a lot easier. I have to go with 3/4", but I think that should work if I need to.

Thanks again!
Bill

[speedster]

Nothing wrong with big bolts but the size of bolts isn't nearly as important as the number of bolts and their placement.  Looking back at some old parametrics, going from 1/2" bolts to 5/8" on an 8 bolt pattern cuts out 0.007 arcsec.  Going from 3-4 bolts to 8 bolts can have 14x that effect.    We use 5/8" bolts not for the strength but because they have longer thread length than smaller bolts and we need the thread length for the base plate thickness (bending moment is max at the base plate).

 

Leveling is basically the same regardless of the number of bolts.  For 4 bolts, you level the north-south nuts and then level the east-west nuts.  For 6, run 3 nuts down just a bit and level the remaining nuts as you would for just 3 bolts and then run the other leveling nuts back up to contact the the plate.  It's like leveling a tripod by leveling in the east-west direction and then adjust the third leg to adjust in the north-south direction.  Process for 8 bolts and up is like 4 bolts. 

[norvegicus]

I find an even number of bolts easier to level.

[coronalight]

I like having 3 leveling points, there is never any conflicting forces between 3 points. To level I put a small level in line with the bolt I am going to either raise or lower, then rotate 120 degrees and do another, repeat this sequence and as you go around you will see there will be minimal, if any additional adjustment needed. I have a circular bubble level but find it confusing to either level this pier, or level my camper.

 

Aside from the number of bolts discussion - how did you get such a nice round and smooth concrete base like that? 

 

Looking to pour a concrete base for a steel pier and appreciate any tips/suggestions to get a similar result. Yours looks great!

[Victory Pete]

Aside from the number of bolts discussion - how did you get such a nice round and smooth concrete base like that? 

 

Looking to pour a concrete base for a steel pier and appreciate any tips/suggestions to get a similar result. Yours looks great!

20" Sonotube and I patiently finished the top while the concrete was curing. I had a mix-up with the specs for the C120 pier converting from metric to SAE and would have used a 22" tube, if it was even available. My bolts may be a bit close to the edge considering I drilled them afterwards. I used every size incrementally I could get up to 1 1/2", it took a while, but it made sure the bits didn't wander too much while drilling. I use a concrete brick to round over the sides slightly after the concrete has set up a bit. It also works to "sand" the concrete also if you do it with some kind of concrete feather patch that is pretty loose, there are a lot of specialty concretes available these days. I use a 4" wide really fine paint brush with some of that loose mixture concrete to give it a final wash. Also make sure as you are pouring, especially at the end, to work in the concrete to remove air and to let it settle against the Sonotube, as you work it the water will come to the top, giving a smooth final surface. I am in construction and worked for a mason in the early days.

 

https://www.cloudyni...way/?p=12919409

 

 

https://www.cloudyni...way/?p=13004462

Edited by Victory Pete, 08 July 2024 - 04:02 PM.

[KTAZ]

Nothing wrong with big bolts but the size of bolts isn't nearly as important as the number of bolts and their placement.  Looking back at some old parametrics, going from 1/2" bolts to 5/8" on an 8 bolt pattern cuts out 0.007 arcsec.  Going from 3-4 bolts to 8 bolts can have 14x that effect.    We use 5/8" bolts not for the strength but because they have longer thread length than smaller bolts and we need the thread length for the base plate thickness (bending moment is max at the base plate).

 

Leveling is basically the same regardless of the number of bolts.  For 4 bolts, you level the north-south nuts and then level the east-west nuts.  For 6, run 3 nuts down just a bit and level the remaining nuts as you would for just 3 bolts and then run the other leveling nuts back up to contact the the plate.  It's like leveling a tripod by leveling in the east-west direction and then adjust the third leg to adjust in the north-south direction.  Process for 8 bolts and up is like 4 bolts. 

I agree with Speedster; 4 bolts is better than 3 and easier to level, IMHO. If you can do 6, do 6, but many of us use square base plates, so 4 it is.

 

YMMV.

[Victory Pete]

I agree with Speedster; 4 bolts is better than 3 and easier to level, IMHO. If you can do 6, do 6, but many of us use square base plates, so 4 it is.

 

YMMV.

I don't think it gets any easier than leveling 3, also, there is no way to have any internal stresses in the pier's baseplate. No matter how marginal, there could be some deflection of the base plate with 4. Like a 3-legged stool that will always have the same load on each leg. My C120 pier came with 3, so naturally I used 3. It seems they designed it with enough reinforcement to the base that 3 support holes deemed adequate.

 

https://www.primaluc...crete-base.html

[joshman]

Some considerations that might help you decide:

 

In a typical pier application, deflection is independent of weight.  Deflection is the same whether the load is 30# or 300#.

 

High performance piers are necessarily heavy.  No economical way around that.  But, there are ways to safely handle a heavy pier without equipment - even with only one person.  You only have to move one end at a time.

 

Clay + water = movement.  It's nice to get below the most active surface soils but it's no crisis.  It just means you may be touching up PA every now and then. 

 

Multi-section piers can be fine if you use enough bolts in the connection so that the pieces can be considered bonded and therefore a single unit after assembly.  The down side is cost.  Each section cost about the same as a whole pier due to fabrication of additional plates.

 

Multi-piece piers can be fine but there is little weight savings for the same performance and the cost is very much higher.  Connection design is different, as well as some other things, but it can certainly be done.

The ATS tripod has a small foot radius so instead of 3 independent footings, you could enlarge the pier cap a bit and catch all 3 legs on one foundation.

 

Tripods are an excellent structural shape but we introduce problems when we make them portable.  Stiffness is sacrificed for lighter weight (aluminum is 3x more flexible than steel) and in all the hinges and connections for folding can be sources of arcsec deflection. 

 

Another option is to use the tripod since you already have it and see if it meets your needs.  Tighten all the joints or put them in a bind so that it is no longer collapsible to try to take out any wiggle.  If that works for you, you can attach the legs to the foundation with some clip angles.

 

No need to be concerned about resonance.  Everything vibrates. Even the back of your eye has a resonant frequency. A telescope pier has not one but several modal frequencies. Fundamental frequency corresponding to first modal shape is called natural frequency of the system. Increasing stiffness increases the natural frequency. Increasing the mass decreases the natural frequency. An increase in the damping diminishes the peak response but broadens the response range. What does this mean to a properly designed telescope pier? Absolutely Nothing! Since the magnitude of the vibration is less than the deflection, less than the camera can detect, it doesn’t matter if it’s vibrating at 40 Hz, 400 Hz, or 4,000 Hz.

Thank you for the input Jim. I've decided that a more traditional pier construction would be the way to go. I'll still need to workout the footing, but i have some retaining walls to make that will require an engineers input, so I might add this consideration to the list.

 

This is what I've got designed at the moment. The pier is 1m tall, the central column is 220mm OD steel with an 8mm wall, as this is what is available at my local fabricator. The base flange is 20mm thick x 320mm OD and the orange top plate is 20mm thick x ~260mm OD (dimensioned for the AP-1612FSA). I would have the Orange top plate be removeable/bolted to the pier Top. I've got the top-plate designed/laid out for the Astro-Physics Flat surface adapter plate (1612FSA)

I'm tempted to make the vertical grey plate a bolt-on attachment, the purpose would be to install a small enclosure to house the data/power/etc

 

 

I may make the pier slightly shorter, considering my own height, but I'll need to work out what I'm doing with the surrounding floor first. Considering my mount is an AP1200GTO, Are there any considerations or additions I can make to make this the best pier I possibly can?

 

[speedster]

Bear in mind that the 1612FSA adapter's bolt pattern is only slightly larger than the pipe o.d.  Through-bolts to attach the ring are not an option but you can drill and tap the mount plate and attache the ring with short bolts that don't extend below the plate.  A bevel weld will give you more room than a fillet weld but it's still awfully tight. 

 

A flat surface can use the anchor bolts as hard points for attachment and avoid the fussiness of connecting a flat plate to a curved surface.  A Benton tab like this, using three adjacent anchor bolts on the south side of the pier:

 

 

(this pier is also prepped for the 1612FSA)

Edited by speedster, 12 July 2024 - 05:10 PM.

[joshman]

Bear in mind that the 1612FSA adapter's bolt pattern is only slightly larger than the pipe o.d.  Through-bolts to attach the ring are not an option but you can drill and tap the mount plate and attache the ring with short bolts that don't extend below the plate.  A bevel weld will give you more room than a fillet weld but it's still awfully tight.

The the ATS pier adapter offered by AP specifies ~15mm deep holes for screws that hold the FSA to the pier adapter. With a 20mm thick top plate I can get the FSA mounting holes blind drilled and tapped to that depth pretty easily.

 

I don't know how to go about the deflection calculations or structural analysis, but is there anything i can do to stiffen the pier even further? 20x20 Vertical ribs the full height? Is it even necessary? I do plan on exploring some long focal length imaging down the line.
 

A flat surface can use the anchor bolts as hard points for attachment and avoid the fussiness of connecting a flat plate to a curved surface.  A Benton tab like this, using three adjacent anchor bolts on the south side of the pier:
 
telescope pier 3.jpg
 
(this pier is also prepped for the 1612FSA)

Can you send me one of those piers... for testing?
 
That flat plate mounted to the pier bolts is a much better arrangement altogether, good to know i'm on the right path with some of my thinking.

[speedster]

No stiffeners needed.  You're in good shape with the sizes you have selected.  Look at 8" 150 SO Flange.  For DIY piers, much better than most anything else you can do and also a good deal less money.

[joshman]

No stiffeners needed.  You're in good shape with the sizes you have selected.  Look at 8" 150 SO Flange.  For DIY piers, much better than most anything else you can do and also a good deal less money.

Thanks for the pointer, the 8" flange in this list looks to be exactly what i need. Given the fab time for a guy to make this, the price seems relatively reasonable. ~221mm ID, ~340mm OD, with a Bolt Circle of ~300mm,  https://thornado.com...eel-asme-b16-5/
 

Edit:

This is more economical. I'm not well versed in the steel types, but this is plate steel verse the carbon steel above. not sure which is better? https://thornado.com...-en1092-1-pn16/

Edited by joshman, 13 July 2024 - 10:44 PM.

[macdonjh]

Thanks for the pointer, the 8" flange in this list looks to be exactly what i need. Given the fab time for a guy to make this, the price seems relatively reasonable. ~221mm ID, ~340mm OD, with a Bolt Circle of ~300mm,  https://thornado.com...eel-asme-b16-5/
 

Edit:

This is more economical. I'm not well versed in the steel types, but this is plate steel verse the carbon steel above. not sure which is better? https://thornado.com...-en1092-1-pn16/

That was a weird website.  EN1092-1 is the British dimensional standard for pipe flanges (the British equivalent of ASME B16.5 in the US).  I didn't see any material specifications at all.  "Plate steel" is kind of like saying something is made out of "plastic", there are many possibilities. 

[speedster]

Either will be fine.  ANSI flanges are a bit more robust for higher pressures and temperatures.  They are also Imperial whereas DIN flanges are metric.  In the U.S., ANSI flanges are common and DIN flanges are a bit rare.  Outside the U.S., just the opposite.  If you are using metric pipe, 200mm, use a DIN flange.  If you are using Imperial pipe, 8", use an ANSI flange.  Actually, I think they are interchangeable but don't take my word for that.

[Shannon Foye]

Looking back at some old parametrics, going from 1/2" bolts to 5/8" on an 8 bolt pattern cuts out 0.007 arcsec.  Going from 3-4 bolts to 8 bolts can have 14x that effect.

This is interesting. Can you post some more information regarding the amount of deflection that the base plate contributes to deflection with different bolt arrangements? Perhaps a table showing the reduction in deflection as the number of bolts increase.

[speedster]

The design brief was to economically get piers below 0.5 arcsec.  A table would be a mess because we have to look at deflection of the entire assembly and there are ranges of variables for number of bolts, bolt diameter, distance from pipe, base plate thickness, pier height, etc.  Are eight 5/8" bolts 1.25" from the pipe better than twelve 1/2" bolts 2" from the pipe?  As I remember, we started with a 6-bolt model and it wouldn't work unless the base plate thickness got ridiculous so we went to an 8-bolt model and it worked with a more reasonable 1" base plate so we tried a 10-bolt model to see how much difference it made and then stopped there because 10 didn't give us significant advantage and moved on to other variables.  So, a table of the number of bolts would only have 3 hard data points and pier performance would also depend on plate thickness, bolt distance from pipe, etc.  So, about all I can say is that more bolts are better in general, there is diminishing return on more bolts, and 6 wasn't enough to hit the 0.5 arcsec target but 8 was if we minimized the bolt distance to the pipe by using a bevel weld instead of a fillet and switching from USS to SAE washers on top of the base plate.  It does take some tricks to get the very low deflection numbers but a "by-the-book" DIY pier can come very close.  You have to optimize the blue to affect the red:

 

Edited by speedster, 22 July 2024 - 12:31 AM.

[Victory Pete]

The design brief was to economically get piers below 0.5 arcsec.  A table would be a mess because we have to look at deflection of the entire assembly and there are ranges of variables for number of bolts, bolt diameter, distance from pipe, base plate thickness, pier height, etc.  Are eight 5/8" bolts 1.25" from the pipe better than twelve 1/2" bolts 2" from the pipe?  As I remember, we started with a 6-bolt model and it wouldn't work unless the base plate thickness got ridiculous so we went to an 8-bolt model and it worked with a more reasonable 1" base plate so we tried a 10-bolt model to see how much difference it made and then stopped there because 10 didn't give us significant advantage and moved on to other variables.  So, a table of the number of bolts would only have 3 hard data points and pier performance would also depend on plate thickness, bolt distance from pipe, etc.  So, about all I can say is that more bolts are better in general, there is diminishing return on more bolts, and 6 wasn't enough to hit the 0.5 arcsec target but 8 was if we minimized the bolt distance to the pipe by using a bevel weld instead of a fillet and switching from USS to SAE washers on top of the base plate.  It does take some tricks to get the very low deflection numbers but a "by-the-book" DIY pier can come very close.  You have to optimize the blue to affect the red:

 

MOAP 43 solution.jpg

Why no rocket fins? It seems to me that they would increase the stiffness quite a bit.