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Please help a newbie design a pier for the backyard

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#1 Ihtegla Sar

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Posted 28 October 2020 - 11:52 AM

I am planning eventually to build a small domed observatory in the corner of the yard for visual use only.  I had originally not planned to put a pier in since I wanted flexibility to put my big dob in the observatory at times, to use a tripod where I could easily adjust the height and also to be able to easily move the observatory if I ever move to another house. 

 

This post in another thread convinced me that the best solution would be to pour the concrete pier base below the floor level of the observatory and bolt on a metal pier.  That way I would have all the benefits of a pier and could do AP if I wanted, but could easily take the pier out if needed.

 

I have no idea how to build something like that, and after googling around a bit, I was hoping for some help and guidance from all you fine experienced folks here.

 

There are a few complicating factors.  The only suitable area for an observatory on my property is at the edge of a gravel parking area with half of the observatory on flat land and the other half extending over a fairly steep slope.  The pier would be on the sloped ground.  The slope is about 50%.  There is also some fill here that was left over from the grading  for the house so they leveled off an area for some extra parking.  

 

I will probably get help from a builder to pour the concrete (I have a good builder to work with  but he doesn't have any experience with astronomy), but I need to know how deep and wide the hole needs to be, what type of internal reinforcements to use and what type of bolts I need to set in the concrete in order to add a mount plate, where to get a mount plate, recommendations on metal piers to attach to the mount plate, etc.

 

I don't know what telescope I will put on the pier but probably something like a TEC 140 or 160 on a G11 mount, none of which I own at the moment.  For now it will jsut be my Tak FC100DL on a LX70, but I want the pier to be sufficient for heavier telescopes than the Tak.

 

Any advice or suggestions?

 

 

 

 



#2 StephenW

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Posted 28 October 2020 - 12:31 PM

If you put your pier on a 50% slope then you will also (eventually) be putting your domes observatory in the same location?   Sounds like it could be a challenging future build.

 

Regarding the specifics on building a concrete pier - if you search on this forum there are many, many posts on what is needed to do this. 



#3 macdonjh

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Posted 28 October 2020 - 04:21 PM

A really good place to start learning about piers: https://www.cloudyni...n#entry10355725

 

As StephenW says, search the Observatories forum for "pier design" and you'll see dozens of threads as well. 


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#4 Peterson Engineering

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Posted 29 October 2020 - 09:43 AM

Hi Steve,

 

A pier requires vibration resistance but you don't need load bearing strength as just abut anything will support hundreds of pounds as long as the weight's centered on the pier.

 

Observatories come and go.  But piers can be a **** to remove and you should consider your situation sometime in the future.  This might not seem like a biggie right now but down the line.......

 

Fabrication of a custom steel pier bolted to a concrete foundation is going to be very expensive.  Particularly as you're probably talking a 7 or 8' length of 5" or larger diameter pipe.

 

Filling a sonotube with rebar and concrete is a common solution.  But to keep things simple, keep costs down, optimize performance and allow for future removal I suggest consideration of a stack of cinder blocks.  Mount the blocks in a hole that goes below the frost line.  Pour concrete into the hole and use mortar to join 2 cinder blocks for each level.  Don't use rebar. 


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#5 Ihtegla Sar

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Posted 30 October 2020 - 11:52 AM

Hi Steve,

 

A pier requires vibration resistance but you don't need load bearing strength as just abut anything will support hundreds of pounds as long as the weight's centered on the pier.

 

Observatories come and go.  But piers can be a **** to remove and you should consider your situation sometime in the future.  This might not seem like a biggie right now but down the line.......

 

Fabrication of a custom steel pier bolted to a concrete foundation is going to be very expensive.  Particularly as you're probably talking a 7 or 8' length of 5" or larger diameter pipe.

 

Filling a sonotube with rebar and concrete is a common solution.  But to keep things simple, keep costs down, optimize performance and allow for future removal I suggest consideration of a stack of cinder blocks.  Mount the blocks in a hole that goes below the frost line.  Pour concrete into the hole and use mortar to join 2 cinder blocks for each level.  Don't use rebar. 

Thanks.  So it sounds like I don't really have to worry too much about the structural strength of the pier/pier base as long as it is below the frost line and is basically plumb. I will want the pier to support a big refractor -- planning for a six inch f/8 but would want it to support something bigger (up to 8") just in case.  

 

I have read the thread macdonjh posted but that thread is 10 pages long with a log of confusing information -- too much information and left me a bit confused and overwhelmed.  But it sounds like I was overthinking the structural issues.

 

My thought about using a removable pier was to purchase a metal pier like an iOptron that is 900mm long for $500, and for a couple hundred bucks more they will make it taller.  I was thinking about 4 feet long would be enough to come up through floor and be the right height for mounting a refractor, since there will also be a pier adaptor and a mount on top of the pier and some mounting bolts below.  I am planning on 4 foot walls in the observatory with a dome on top.  

 

The idea of a concrete block pier is a good one since the ability to remove the pier is something I want to design in, in case I end up moving.  I will want to be able to demolish the pier from inside the observatory so I can jack up the observatory and load it onto a trailer to take it with me.  I will be building it on skids mounted on concrete deck footings.  So the concrete block pier would work, although it wouldn't let me put the dob in the observatory the way a removable iOptron pier would.  But the concrete block pier would let me adjust the height since it would be easy to add or remove a layer of blocks once the observatory is done if I decided I needed a little more or less height.



#6 Peterson Engineering

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Posted 30 October 2020 - 12:55 PM

A concrete block foundation works wonderfully well for the observatory itself.  Just support the 4 corners on the blocks.  Didn't know about iOptron's pier.  Mine cost far more and I've got the shops to build it.  Great value and it'll look better than a stack of blocks that you have to work around.  I couldn't sell one for less than $1300.  As for height, you need to sketch out a to-scale picture of the dome wall height and the desired sccope height.  Need to clear the wall at perhaps 20° above the horizon and still have a comfortable viewing/working position.


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#7 macdonjh

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Posted 30 October 2020 - 09:39 PM

If you're willing to do a bit of research into local businesses, perhaps you can find a local fabricator- there's nothing special about a pier, they are simple.  Here on the Third Coast, oil and gas are big so it's easy to find welders and scrap pieces of pipe.  Even if you're in a part of the Pacific Northwest not involved with oil and gas, perhaps there are some architectural fabricators who use rectangular tubing on a regular basis.  The fabricator really only needs to know how tall and the bolt pattern for the bottom (to bolt to your foundation/ footer) and the bolt pattern for your mount.  That way they know what holes to drill...



#8 Peterson Engineering

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Posted 31 October 2020 - 11:46 AM

Simple.  But not simple.  Took a while before I sourced the appropriate pipe at a junkyard.  Had to cut it to length. Purchased two square plates to weld top and bottom of pipe plus one aluminum plate for mounting.  Drilled large diameter holes into the bottom plate and matching holes into the two top plated.  Welded. And assembled the mounting plate on standoffs over the top pier plate.

 

This sucka  is HEAVY.  And even thought the concept is simple, it's a pain to locate material.  And it takes some industrial strength equipment to cut/weld/drill this heavy material.

 

Even though Peterson Engineering has huge fabrication capability I've found it almost always best not to reinvent the wheel if something is already out on the market.



#9 macdonjh

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Posted 01 November 2020 - 09:02 AM

Simple.  But not simple.  Took a while before I sourced the appropriate pipe at a junkyard.  Had to cut it to length. Purchased two square plates to weld top and bottom of pipe plus one aluminum plate for mounting.  Drilled large diameter holes into the bottom plate and matching holes into the two top plated.  Welded. And assembled the mounting plate on standoffs over the top pier plate.

 

This sucka  is HEAVY.  And even thought the concept is simple, it's a pain to locate material.  And it takes some industrial strength equipment to cut/weld/drill this heavy material.

 

Even though Peterson Engineering has huge fabrication capability I've found it almost always best not to reinvent the wheel if something is already out on the market.

Point taken.  The design of a pier is pretty simple, though.  If you live in certain places, the materials are easy to come by.  I live where oil and gas is big business so pipe and steel plate are easy to get.  And those with the right tools can make relatively quick work of the fabrication.  Granted, those tools are not typically found in somebody's garage.  Again, where I live, there are lots of small companies who can cut and weld and are willing to take on small one-off projects after hours and on weekends for a bit of extra cash.

 

Of course, finding all those resources takes time and energy.  It may be preferable to simply purchase a pier from somebody and start using it.  Somebody, somewhere, is going to have to do some work to make your pier.  If you like designing, tinkering and building (or having building done), it's not a complicated project but it will still take time and money.  If you don't like that stuff, perhaps spend your time at your day job and pay somebody else to do the designing and building.



#10 Ihtegla Sar

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Posted 01 November 2020 - 12:46 PM

Point taken.  The design of a pier is pretty simple, though.  If you live in certain places, the materials are easy to come by.  I live where oil and gas is big business so pipe and steel plate are easy to get.  And those with the right tools can make relatively quick work of the fabrication.  Granted, those tools are not typically found in somebody's garage.  Again, where I live, there are lots of small companies who can cut and weld and are willing to take on small one-off projects after hours and on weekends for a bit of extra cash.

 

Of course, finding all those resources takes time and energy.  It may be preferable to simply purchase a pier from somebody and start using it.  Somebody, somewhere, is going to have to do some work to make your pier.  If you like designing, tinkering and building (or having building done), it's not a complicated project but it will still take time and money.  If you don't like that stuff, perhaps spend your time at your day job and pay somebody else to do the designing and building.

You bring up a good point about DIY.  Is there any reason I couldn't just make a removable pier post out of wood?  It doesn't seem like it would be that hard or expensive to design and build a wood post to whatever height was needed that had top and bottom plates attached with holes drilled to match the appropriate bolt spacing.  If I used longer bolts, I could make the top and bottom plates out of wood too.  I can get a pressure treated 6x6 landscape timber for thirty bucks at home depot and then lag bolt some square pieces of 2x8 to each end.  The top one could have bolts facing up to attach to the mounting plate and the bottom could have holes in it to slip over the bolts coming up out of the concrete.



#11 Peterson Engineering

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Posted 01 November 2020 - 05:10 PM

I'd forgotten about wood.  A buddy in NM is using wood and it's easily removed at end of life.  Heavier is better.  But dried is critical.  Wonder how one would obtain the end of a dead telephone pole..........



#12 macdonjh

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Posted 02 November 2020 - 10:25 AM

You bring up a good point about DIY.  Is there any reason I couldn't just make a removable pier post out of wood?  It doesn't seem like it would be that hard or expensive to design and build a wood post to whatever height was needed that had top and bottom plates attached with holes drilled to match the appropriate bolt spacing.  If I used longer bolts, I could make the top and bottom plates out of wood too.  I can get a pressure treated 6x6 landscape timber for thirty bucks at home depot and then lag bolt some square pieces of 2x8 to each end.  The top one could have bolts facing up to attach to the mounting plate and the bottom could have holes in it to slip over the bolts coming up out of the concrete.

Wood would work, there are just a couple of issues.  I agree with Peterson Engineering: use properly dried lumber.  To that end I would not use pressure treated wood if it was my pier.  That stuff is soaking wet and warps and twists like crazy as it dries.  The issue I have with wood for a pier is over the course of weeks and months it isn't stable.  You'll find your polar alignment doesn't "hold" and you'll have to adjust it from time to time.  That may not be a big deal to you, but you should be aware of it going in so you won't be frustrated when it happens.

 

As for the DIY route: I made my pier out of concrete for that reason.  I didn't want to use wood, I don't know how to weld, but I do have basic concrete skills.  As for adapter plates and other bits, you can get small pieces of aluminum plate from the internet (quite expensive on a per-pound basis, but you're not buying much) and aluminum is so soft you can do basic things like drilling holes with wood-working tools.  I know you don't want to use concrete, I only bring it up because it's an alternative for those who want to build the whole thing themselves.

 

Even with my concrete pier I decided to true-up my polar alignment: it just took a bit over four years before I decided I wanted to do it.  My pier is pretty stable.


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#13 kathyastro

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Posted 02 November 2020 - 10:44 AM

Is there any reason I couldn't just make a removable pier post out of wood?

Although I have heard of people making piers out of solid wood, such as telephone poles, wood is generally too flexible for a satisfactory pier.  Your engineering has to be good to make it a satisfactory pier.

 

I built mine out of 1/2" plywood.  When I first proposed a plywood pier, an engineer friend suggested that a tapered column would be more rigid than anything straight-sided.  I took his advice, and that's what I have been using for more than seven years.

 

Here are a couple of photos of the pier being assembled:

 

P1090216-1000px.JPG

 

P1090219-1000px.JPG


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#14 Peterson Engineering

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Posted 02 November 2020 - 11:45 AM

Man oh man!  A plywood pier.  That's really neat and hugely functional.  The wedge shape isn't necessary as the sides provide mega-stiffness, but it does look nicer for sure.  What a nice job.


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#15 Ihtegla Sar

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Posted 02 November 2020 - 01:16 PM

Thanks for all the tips about wood piers. Sounds like the iOptron metal pier would be better but its good to have options in case there is an issue with getting the iOptron pier.  Looks like they are on backorder right now.  Hopefully they will be available by the time I actually need one.  My Exploradome is six weeks overdue and the construction season is pretty much over so it might be next spring before I actually start building anything.



#16 speedster

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Posted 03 November 2020 - 02:15 AM

Engineered wood is an excellent and under rated choice.  The sloped sides of Kathy's pier do reduce deflection as the moment of inertia of a 10" box is double that of an 8" box.  I'll do a part 3 to the pier engineering thread and post in a bit.



#17 D_talley

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Posted 05 November 2020 - 05:37 AM

Here are my piers that Pete was taking about. Built with 4 x 6x6 that are planted 3.5 feet deep. Each 6x6 is glued and screwed to the others so that there is no twist or bending.  Being in the desert I don't have any issues with moisture as well.  When I move I can pull them out without needing dynamite.  i would not use anything smaller than four 6x6. There is too much warp and twist in the 4x4 I see for sale. 

Attached Thumbnails

  • padinplace.jpg
  • twopiershole.jpg

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#18 Peterson Engineering

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Posted 05 November 2020 - 06:43 AM

If the telescope center of gravity is centered over the pier Dwight's approach is pretty darned good.  And one of the two supports a setup exceeding 100#.



#19 Cosmo Geezer

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Posted 09 November 2020 - 08:34 PM

I used a 4x4 treated wood post set in concrete outside in the backyard for 3 years with no problems. When I built the Mollie Brown Observatory I installed a 6x6 treated wood post set in 300 lbs of concrete. Been operational for 1.5 years with no problems. Humidity doesn't get any worse than in Northwest Alabama in the summertime. Just saying.



#20 D_talley

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Posted 09 November 2020 - 09:55 PM

Glad to hear that the 4x4 wood worked for you.  That will give people more options.  You can keep the humidity. smile.gif



#21 Ihtegla Sar

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Posted 13 November 2020 - 12:52 PM

Although I have heard of people making piers out of solid wood, such as telephone poles, wood is generally too flexible for a satisfactory pier.  Your engineering has to be good to make it a satisfactory pier.

 

I built mine out of 1/2" plywood.  When I first proposed a plywood pier, an engineer friend suggested that a tapered column would be more rigid than anything straight-sided.  I took his advice, and that's what I have been using for more than seven years.

 

Here are a couple of photos of the pier being assembled:

 

attachicon.gifP1090216-1000px.JPG

 

attachicon.gifP1090219-1000px.JPG

 

That looks like some good carpentry!  Can I ask how you connected the joints, is it just glue, or did you use any hardware?

 

Also how did you attach it to the ground/floor, and how do you attach a mount?  Since its thin plywood I am guessing that you can't just lag bolt a metal plate to it like you could with those solid wood piers.  I'm curious what type of hardware you used to make the attachments?


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#22 kathyastro

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Posted 13 November 2020 - 01:41 PM

That looks like some good carpentry!  Can I ask how you connected the joints, is it just glue, or did you use any hardware?

 

Also how did you attach it to the ground/floor, and how do you attach a mount?  Since its thin plywood I am guessing that you can't just lag bolt a metal plate to it like you could with those solid wood piers.  I'm curious what type of hardware you used to make the attachments?

Thanks!

 

The sides and internal stiffening shelves are attached with glue and finishing nails.  The top is 3/4" plywood.  Holes are drilled in the top for 5/8" bolts to hold a Dan's pier plate.  The "window" at the top of the pier in the second photo is to access the undersides of the bolts.  The upper stiffening shelf is positioned where it is to catch dropped nuts and washers.

 

The base is three layers of 3/4" plywood.  The upper layer is 16"x16", and is internal to the pier column.  The lower two layers are 24"x24", glued and screwed together to make a 1.5" single piece.  In the original installation, it stood on blocks of 2x4 (replaceable in case of rot), visible in the photos.  The pier stood on hard-packed crusher dust, and was held in place by four 1.25" steel rods driven 4' into the ground.  The rods pass through holes drilled in the plywood base, which are visible in the photos.

 

In the new installation, at a new site, the base sits on J-bolts protruding from the top of a concrete foundation.  The first installation was the more rigid of the two, although I am quite happy with the current installation.


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#23 mikenoname

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Posted 14 November 2020 - 03:02 AM

The idea of a concrete block pier is a good one since the ability to remove the pier is something I want to design in, in case I end up moving.  I will want to be able to demolish the pier from inside the observatory so I can jack up the observatory and load it onto a trailer to take it with me.  I will be building it on skids mounted on concrete deck footings.  So the concrete block pier would work, although it wouldn't let me put the dob in the observatory the way a removable iOptron pier would.  But the concrete block pier would let me adjust the height since it would be easy to add or remove a layer of blocks once the observatory is done if I decided I needed a little more or less height.

 

Concrete blocks is what worked best for my situation.

 

My Setup_s.jpg

 

The blocks are glued to each other with construction adhesive. The DIY wooden wedge is glued to the top block with the same adhesive and stays outside permanently polar aligned. However, the bottom blocks are not glued to the concrete pad so that I can easily move the pier with a fridge dolly whenever needed.

 

Of course in my case the blocks and wood were already hanging around the property (my landlord is a pack rat LOL) so they were free and on hand which helped motivate this particular 'design'.



#24 Peterson Engineering

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Posted 14 November 2020 - 09:06 AM

I've never seen cinderblocks stacked that way. The cinderblock piers I've seen have always been 2 blocks wide and with the holes vertical.to maximize rigidity.



#25 mikenoname

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Posted 20 November 2020 - 11:20 PM

I doubt a concrete block is less rigid in one direction vs another when there is a total of ~40 pounds on it. And besides, with the holes horizontal they make great places to stash things like hand controllers, batteries, covers, lights, cameras, etc.




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