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dawziecat
Carpal Tunnel
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Reged: 10/20/10

Loc: Rural Nova Scotia
Pier diameter?
      #6036622 - 08/20/13 02:21 PM

I am getting ready to commence building a Skyshed roll-off roof observatory.

I already seem to have made my first mistake. I bought a sonotube and Bigfoot thinking an 8" pier would be about right. But, when thinking through how an AP1100 would actually attach to the pier, it appears 8" is not nearly wide enough? I am now thinking a 14" pier is about right. It matters a great deal that this pier not get out of hand as concrete has to be mixed and poured by hand! Redi-mix truck access is just not possible. Going from 8" to 14" has already meant the wheelbarrow will be insufficient for mixing 23 eighty LB bags of pre-mix and I will have to rent a small mixer.

I enlist the opinion of any who have gone this pier route before for guidance on the matter. Pier footing will be put below frost line (4 feet here). I hope to have a steel plate 3/8" thick fabricated to allow mounting of the Astrophysics 119FSA ("flat surface adapter"). The plate will fit onto four threaded half inch rids or J bolts embedded in the pier, thereby providing for a level adjustment.

Edited by dawziecat (08/21/13 11:03 AM)


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Aquarist
scholastic sledgehammer


Reged: 08/27/12

Loc: Illinois
Re: Pier diameter? new [Re: dawziecat]
      #6036663 - 08/20/13 02:40 PM

Well ATS recommends for Astro-Physics AP 900GTO Mounting (AP adapter)an 8 inch pier and for an Astro-Physics - AP 1600GTO Mounting (AP adapter), a 10 inch pier.

Edited by Aquarist (08/20/13 03:14 PM)


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roscoe
curmudgeon
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Reged: 02/04/09

Loc: NW Mass, inches from VT
Re: Pier diameter? new [Re: dawziecat]
      #6036682 - 08/20/13 02:47 PM

Terry,

I admit to being a frugalist/minimalist, but I also have been a carpenter for many years, and mixed many a bag of premix in my day.....and it's my private belief that most ATM scope piers could nearly anchor one end of the Golden Gate Bridge......so it certainly seems to me that 8 would do the trick, 10 would be plenty rugged unless you were hanging a huge refractor on it..... Mine, built to accommodate a (still in the 'hopefully pretty soon' stage) 6" f/12 refractor, is 10 to a bit above ground level and 8 for another 4 1/2 feet. If I kick it hard, it'll jiggle an image for a couple of seconds, but I don't kick it very often in real life......... it seems to handle a 120/8 effortlessly.....

Russ


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Gastrol
Pooh-Bah


Reged: 11/04/11

Loc: los angeles
Re: Pier diameter? new [Re: roscoe]
      #6036703 - 08/20/13 03:01 PM

I agree most poured piers are a complete overkill. I personally would follow aesthetics and determine a pleasing diameter relative to length and the mount it will be supporting.

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Kraus
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Reged: 03/10/12

Loc: Georgia.
Re: Pier diameter? new [Re: Gastrol]
      #6036733 - 08/20/13 03:16 PM


My pier is 12 inch diamter, three feet tall. I got the form from Lowe's. A big bucket is useful for mixing cement. Six bags for a solid base and four bags to fuill the tube-a-dube-dube.


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Christopher EricksonModerator
Carpal Tunnel
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Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Pier diameter? new [Re: Kraus]
      #6036822 - 08/20/13 04:00 PM

A concrete pier can be hollow and not lose any of its rigidity.

Two concentric Sonotubes can do the trick and save you a lot of grief in concrete work, expense and weight.

The concrete wall thickness should not be thinner than 2".

You can also insert a short piece of PVC pipe through the two Sonotubes near the base and route cables inside the hollow pier.

Make sure to put metal mesh between the two Sonotubes for concrete strength.

The center of any pier contributes nothing to the rigidity of that pier.

My rule of thumb is a concrete pier diameter no smaller than the aperture of the scope that will be put on it.

If the pier is more than four times taller than it's diameter, increase the diameter of the pier to maintain at least a 4:1 ratio, or better.

If you decide to cheat a bit, do not exceed a 5:1 ratio.

I hope this helps.

Edited by Chris Erickson (08/20/13 04:01 PM)


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tim57064
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Reged: 08/23/12

Loc: Southeast South Dakota,USA
Re: Pier diameter? new [Re: Christopher Erickson]
      #6036847 - 08/20/13 04:12 PM

I have never heard of anyone using a hollow concrete pier for mounting a scope. If that is what you are describing,would that not present more of a problem with vibration transferring to the mount? Curious?

Edited by tim57064 (08/20/13 04:12 PM)


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Christopher EricksonModerator
Carpal Tunnel
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Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Pier diameter? new [Re: tim57064]
      #6036870 - 08/20/13 04:24 PM

Quote:

I have never heard of anyone using a hollow concrete pier for mounting a scope. If that is what you are describing, would that not present more of a problem with vibration transferring to the mount? Curious?




Like I said, the center of a concrete pier contributes NOTHING to the rigidity of the pier.


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tim57064
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Reged: 08/23/12

Loc: Southeast South Dakota,USA
Re: Pier diameter? new [Re: Christopher Erickson]
      #6036879 - 08/20/13 04:32 PM

Would have been nice if I had tried that first instead of building a 16" diameter one 6' high.

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Midnight Dan
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Reged: 01/23/08

Loc: Hilton, NY, Yellow Zone (Bortl...
Re: Pier diameter? new [Re: tim57064]
      #6037068 - 08/20/13 06:18 PM

A lot depends on how far the pier is sticking out of the ground. But for my 2 cents, 8" is not nearly enough.

I just recently put in a pier that is 4 feet in the ground (frostline) and 5.5 feet above the ground. The base is a foot thick and 2 feet in diameter. I started off thinking an 8" or 10" would be fine but I went 12" and am very glad I did. If I put a hand on one side near the top, and give it a good whack with the other hand, I can feel it vibrate. Mind you, it's a small vibration and damps very quickly, and I would never expect the pier to get hit anywhere near that hard in normal use. BUT ... I was surprised to find it vibrate at all. I thought it would be like a rock, but if you get concrete long and thin enough it can act more like a tuning fork.

That AP is a gorgeous mount. Don't short change it with the pier! If your's is 3 to 5 feet out of the ground, you could probably get by with 12", but I think your original plan of 14" is a good one. You only get one shot at this. Yes, it will take extra work at the mixer, but that work will be long forgotten when you're enjoying the observatory.

-Dan


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TimN
Pooh-Bah


Reged: 04/20/08

Loc: Ontario, Canada
Re: Pier diameter? new [Re: Midnight Dan]
      #6037188 - 08/20/13 07:32 PM

I recently put in a pier and used a 14" sonotube with rebars. I then attached a metal pier to the concrete. The local stores had to order it as they only had up to 12". I went down 5 feet to a type of bigfoot. I used a small hand mixer and paid to have the hole dug. My climate would be similar to yours. It may be overkill but I agree with Dan. You only get one shot at it.

Edited by TimN (08/20/13 07:36 PM)


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roscoe
curmudgeon
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Reged: 02/04/09

Loc: NW Mass, inches from VT
Re: Pier diameter? new [Re: TimN]
      #6037206 - 08/20/13 07:42 PM

Another thing to consider is that a tapered pier doesn't suffer from 'tuning fork' vibrations....so while making and securely fastening some plywood rings to your tubes to allow the pier to taper is a whole extra step, it's a good way to build a taller pier....
R

Also, Chris's 'hollow pier' method is a good one that I hadn't thought of......
Another thought, expanding on his 'pvc connector tube' suggestion, would be to install a piece of 3" or 4" PVC drainpipe, with an elbow at the bottom, allowing all manner of wiring to be hidden inside the pier.
R


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dawziecat
Carpal Tunnel
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Reged: 10/20/10

Loc: Rural Nova Scotia
Re: Pier diameter? new [Re: dawziecat]
      #6037217 - 08/20/13 07:49 PM

Well, this is discouraging, really with suggestions all over the clock!

The pier will begin 4'6" below grade with another 4'6" extending above grade.

I appreciate concrete is dirt cheap. And now I actually have an excavator on the property, so digging a hole deep enough to get below frostline is a simple matter.

If it were reachable by a redi-mix truck, I'd say "heck with it," and use a couple of yards of concrete, using concrete as backfill instead of disturbed soil. Sadly, I am just not in a position to do that.

Handling 80 lb bags of pre-mix is not a simple matter for me. Unfortunately labour is scarce hereabouts.

I am not really concerned about "kicking" the pier while imaging. I am concerned about any flexing of the pier and any movement of the pier within the ground caused by the load on the mount shifting slowly as it tracks. This installation is pretty much for astrophotography exclusively with apertures ranging to 10 inches, although a 12" is not out of the question.

I thank all for their opinion in this matter . . . even though I didn't necessarily like the message!

I do appreciate that this is definitely something you don't want to scrimp on! I think that likely goes a long way to explaining why some folks end up with a support that would "hold up the Golden Gate Bridge!"

Edited by dawziecat (08/21/13 06:17 AM)


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roscoe
curmudgeon
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Reged: 02/04/09

Loc: NW Mass, inches from VT
Re: Pier diameter? new [Re: dawziecat]
      #6037467 - 08/20/13 11:10 PM

Terry,

With 9 feet of total pier length, I agree 8" isn't sturdy enough, I think 10" is a better choice here, and won't use a whole lot more concrete.
Two suggestions for keeping it from moving in the ground: If you can, have the excavator make the bottom of the hole as flat as is easily attainable, so the bottom of your pier footing doesn't want to roll around on the base, and as you backfill, tamp or stomp the dirt as firmly as you can - like perhaps in 2" layers, so as to anchor the pier in place as much as possible. Loose backfill, that which has been shoveled back in or dropped with an excavator bucket, does very little to stop pier motion higher up. If your excavator has, or can borrow, a 'thumper', a gas-powered compactor (either the pogo-stick version or the vibrating base-plate version) it'll make your backfill a lot more stable.
You might also find it easier to mix your concrete in a mortar trough, a wood box with vertical sides and slanted ends around 18 x 36 x 8 tall, that you leave on the ground, and mix with a hoe. Much easier than lifting of bags of cement mix up into a wheelbarrow.....

Russ


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wolfman_4_ever
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Reged: 07/15/11

Loc: El Segundo, Ca, So. Cal
Re: Pier diameter? new [Re: tim57064]
      #6037647 - 08/21/13 02:14 AM

Quote:

I have never heard of anyone using a hollow concrete pier for mounting a scope. If that is what you are describing,would that not present more of a problem with vibration transferring to the mount? Curious?




It's one of the reasons why your bones are hollow not to mention bend ability before breakage.


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Midnight Dan
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Reged: 01/23/08

Loc: Hilton, NY, Yellow Zone (Bortl...
Re: Pier diameter? new [Re: dawziecat]
      #6037815 - 08/21/13 07:31 AM

Quote:

Handling 80 lb bags of pre-mix is not a simple matter for me. Unfortunately labour is scarce hereabouts.




When I did my pier, I was able to find someone with a Bobcat that had a fork mounted mixer. This was awesome because the crew could dump several bags into the mixer near the water supply, then take the mix over to the pier and pour it in the top which was over 5 feet off the ground. No wheelbarrows and no lifting!

Bobcats are pretty small and much easier to transport and get to remote locations than a big cement truck. You may want to look into it and see if there's someone nearby that can do this. If they're within 50 miles, it shouldn't be a big deal to get the equipment to you. If you can arrange it, it's well worth the money! Quick and painless:

-Dan



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dawziecat
Carpal Tunnel
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Reged: 10/20/10

Loc: Rural Nova Scotia
Re: Pier diameter? new [Re: Midnight Dan]
      #6038115 - 08/21/13 11:01 AM

Wow, Dan! That's quite the rig. Never heard of that before!
As to one being availabe in my area? Well, odds are not so good. "Slim to none." Likely

I went to a local metal fabricator today. Seems no problem getting a pier-to-119FSA (AP1100 flat surface adapter) interlink fabricated.

It's going to cost me, but I've decided I want no part of humping 80-lb bags about. I will try the local "No-Job-Too-Odd" crew and pay whatever they will charge me. ( I hope they don't monitor this board!!) My wallet is stronger than my back at this stage of life!

(Did I tell you of the morning I threw my back out just before visiting Kitt Peak? Oh, never mind! )


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stmguy
sage


Reged: 10/11/12

Loc: Western NH
Re: Pier diameter? new [Re: dawziecat]
      #6038200 - 08/21/13 11:45 AM

That was one of the main reasons I went with 4ft 12" concrete pier with bigfoot and 40 "'s of well casing cause I didn't want to lift the concrete up into a pier. I parked my mixer right over the pier and poured it right in. It works just fine and reasonably easy to modify if I need to change the height later. I almost wished I went with 14 inch concrete pier as the weldable pipe flange put the anchor bolts pretty close to the outside of the pier but I don't see any issues so far
Norm


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Midnight Dan
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Reged: 01/23/08

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Re: Pier diameter? new [Re: stmguy]
      #6038373 - 08/21/13 01:33 PM

Another way to make things easier, again if the pier isn't too tall, is to put the concrete mixer on the back of a pickup truck.

This is especially handy because you can have the building materials store people load the concrete bags towards the front of the pickup bed when you buy it. Back the pickup up to the pier till the lowered tailgate nearly touches it. Put the mixer on the bed/tailgate and flip the mixing barrel towards the concrete in the front of the bed. Throw a couple bags in, mix with water, and flip the barrel to the other side to pour into the top of the pier.

You, or your crew, will still have to lift the bags to put them in the mixer. But it eliminates handling heavy mixed concrete. If putting the mixer on the pickup bed is just a few inches short of high enough, you can stack some lengths of 2x12 on each other to make a ramp of sorts and gain a few inches. You also have to be sure the pickup tailgate is in decent condition so it will support the weight. Use a drop cloth to keep concrete from spilling onto the tailgate and pickup bed.

Even if you pay a crew, this can really speed things up so you'll have to pay less - assuming you're paying by the hour.

-Dan


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dmdouglass
professor emeritus


Reged: 12/23/07

Loc: Tempe, AZ
Re: Pier diameter? new [Re: Midnight Dan]
      #6038441 - 08/21/13 02:19 PM Attachment (10 downloads)

Check out Home Depot (or Lowes) or any equipment rental location. They rent small portable cement mixers that can be wheeled into location. They usually will do 1 or 2 bags at a time. Easy on the back. Set it up right next to the pour...

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roscoe
curmudgeon
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Reged: 02/04/09

Loc: NW Mass, inches from VT
Re: Pier diameter? new [Re: Midnight Dan]
      #6038466 - 08/21/13 02:36 PM

Quote:

Another way to make things easier, again if the pier isn't too tall, is to put the concrete mixer on the back of a pickup truck.-Dan




Dan speaks well here......this is a common method for construction crews installing sewer grates and manholes and the like, where they need small quantities in many locations.....

and as was also mentioned, many big-boxes and most all rental centers have mixers to loan out, and many carpenters and farmers have one in the yard somewhere that you might borrow.
R


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Pier diameter? new [Re: Midnight Dan]
      #6038545 - 08/21/13 03:13 PM

Why not use reinforced concrete as a foundation and bolt a cylindrical metal pier to that base?

Metal piers more than adequately carry the compression, tension, and torsional loads of any telescope I could imagine ever owning. In addition, should one's needs change (raise or lower the pier height, increase its capacity), one can modify or replace the pier. Finally, it's easier to route cables through a hollow metal pier than through a concrete varietal.

I've used metal portable and permanent piers (the latter bolted to a concrete foundation). There is no movement due to torsional loads caused by the scope off to one side, and there is no seasonal movement of the system.

I think metal piers look better too.


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Christopher EricksonModerator
Carpal Tunnel
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Loc: Waikoloa Village, Hawaii
Re: Pier diameter? new [Re: JJK]
      #6038682 - 08/21/13 04:23 PM Attachment (6 downloads)

Quote:

Why not use reinforced concrete as a foundation and bolt a cylindrical metal pier to that base?

Metal piers more than adequately carry the compression, tension, and torsional loads of any telescope I could imagine ever owning. In addition, should one's needs change (raise or lower the pier height, increase its capacity), one can modify or replace the pier. Finally, it's easier to route cables through a hollow metal pier than through a concrete varietal.

I've used metal portable and permanent piers (the latter bolted to a concrete foundation). There is no movement due to torsional loads caused by the scope off to one side, and there is no seasonal movement of the system.

I think metal piers look better too.




Tubular metal piers are a lot more prone to ringing and vibrations than are concrete piers if you exceed the 1:4 ratio between diameter and height.

Steel X piers are better than tubes (O-piers?) and cool down faster as well.

Edited by Chris Erickson (08/21/13 04:29 PM)


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Pier diameter? new [Re: Christopher Erickson]
      #6039114 - 08/21/13 08:37 PM

Quote:

Quote:

Why not use reinforced concrete as a foundation and bolt a cylindrical metal pier to that base?

Metal piers more than adequately carry the compression, tension, and torsional loads of any telescope I could imagine ever owning. In addition, should one's needs change (raise or lower the pier height, increase its capacity), one can modify or replace the pier. Finally, it's easier to route cables through a hollow metal pier than through a concrete varietal.

I've used metal portable and permanent piers (the latter bolted to a concrete foundation). There is no movement due to torsional loads caused by the scope off to one side, and there is no seasonal movement of the system.

I think metal piers look better too.




Tubular metal piers are a lot more prone to ringing and vibrations than are concrete piers if you exceed the 1:4 ratio between diameter and height.

Steel X piers are better than tubes (O-piers?) and cool down faster as well.




The cool down time and ringing of cylindrical metal piers I've used are non-issues (10" to 12" diameter pier < 40" tall). The latter would generally be of concern if one was prone to constantly rapping on a pier during imaging or visual work, but I suppose it could come into play if there were strong wind gusts hitting a long OTA (a non-issue in an observatory). I've used short and long OTAs on quality metal portable and permanent piers and never had a ringing issue.

I haven't studied the effects of torsional loads on an X-bar, but I also haven't seen any such problem with decent cylindrical metal piers.

Can you please point to a FEA of X-bars versus cylindrical tubes? I've used them in my lab to support micro-manipulators that work in conjunction with microscopes. I hadn't thought about using them for astronomy pier apps.

Edited by JJK (08/21/13 08:55 PM)


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StarmanDan
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Reged: 08/27/07

Loc: Deep in the heart of Texas
Re: Pier diameter? new [Re: JJK]
      #6039210 - 08/21/13 09:38 PM

Don't want to lug around hundreds of pounds of concrete mix, eh? Have you considered a concrete block pier? Mine is a little over 5' above the ground. I was considering filling the blocks with concrete but have found it is quite solid as is and was a cinch to put up and I had never worked with mortar and block construction before. I now have a very solid 16" square pier that will pretty much be able to handle anything I can put on it. All for my dinky 8" SCT.



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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Pier diameter? new [Re: Christopher Erickson]
      #6039247 - 08/21/13 10:01 PM

Quote:

Quote:

Why not use reinforced concrete as a foundation and bolt a cylindrical metal pier to that base?

Metal piers more than adequately carry the compression, tension, and torsional loads of any telescope I could imagine ever owning. In addition, should one's needs change (raise or lower the pier height, increase its capacity), one can modify or replace the pier. Finally, it's easier to route cables through a hollow metal pier than through a concrete varietal.

I've used metal portable and permanent piers (the latter bolted to a concrete foundation). There is no movement due to torsional loads caused by the scope off to one side, and there is no seasonal movement of the system.

I think metal piers look better too.




Tubular metal piers are a lot more prone to ringing and vibrations than are concrete piers if you exceed the 1:4 ratio between diameter and height.

Steel X piers are better than tubes (O-piers?) and cool down faster as well.




Chris, your website is pretty cool & informative.


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Christopher EricksonModerator
Carpal Tunnel
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Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Pier diameter? new [Re: JJK]
      #6039304 - 08/21/13 10:37 PM

Quote:

The cool down time and ringing of cylindrical metal piers I've used are non-issues (10" to 12" diameter pier < 40" tall). The latter would generally be of concern if one was prone to constantly rapping on a pier during imaging or visual work, but I suppose it could come into play if there were strong wind gusts hitting a long OTA (a non-issue in an observatory). I've used short and long OTAs on quality metal portable and permanent piers and never had a ringing issue.

I haven't studied the effects of torsional loads on an X-bar, but I also haven't seen any such problem with decent cylindrical metal piers.

Can you please point to a FEA of X-bars versus cylindrical tubes? I've used them in my lab to support micro-manipulators that work in conjunction with microscopes. I hadn't thought about using them for astronomy pier apps.




I am not aware of anyone doing any serious FEA simulations (Finite Element Analysis) of amateur-class observatory piers but there is certainly a lot of FEA that has been done in and around larger professional observatories. The results would be interesting if someone wanted to go through all of the work to create them.

An "X pier" has more surface area, no dead air spaces and a much-higher surface-area to mass ratio than a tubular or rectangular pier. This isn't likely to matter much in a lab but in an environment where there are temperature swings and you want rapid thermal stabilization, it has advantages.

Unlike research-grade microscopes or precision mechanical laboratory stages, telescope mounts carry heavy, relatively-powerful, active motor assemblies and additional components that are vulnerable to unpredictable external influences. The real challenge for telescope mounts and piers are resonant frequencies and effective damping. In the bad-old-days, this was usually solved for telescopes by lots and lots of mass (more or less.) Nowadays FEA, advanced materials and significant fundamental research have given us much-better tools to work with.

A tubular steel pier does not have near the diagonal rigidity of a steel X pier. An FEA comparison of the two would certainly show that all other things being equal, the X pier would be much more resistant to harmonic vibrations created by wind or the mount's pulsing motors running at different speeds.

And while steel is elastic and concrete effectively is not, steel has a high thermal conductivity that has benefits in an observatory when used carefully.

In "The Design and Construction of large Optical Telescopes, (c) Springer 2010", Section 6 discusses telescope mount mechanical issues at length, including the challenges and limitations of FEA simulations in the design of precision telescope support structures (mount, base & foundation.) It is an excellent reference resource for anyone desiring to build a serious, effective amateur observatory. Be warned that it is filled with math.

I hope this helps.


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Christopher EricksonModerator
Carpal Tunnel
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Loc: Waikoloa Village, Hawaii
Re: Pier diameter? new [Re: JJK]
      #6039326 - 08/21/13 11:02 PM

Quote:

Chris, your website is pretty cool & informative.




Glad you like it.

It isn't much but I had to put up something because my clients expect it these days.

I need to add a lot more content to it but just haven't found the time.


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Pier diameter? new [Re: Christopher Erickson]
      #6039347 - 08/21/13 11:20 PM

Quote:

Quote:

The cool down time and ringing of cylindrical metal piers I've used are non-issues (10" to 12" diameter pier < 40" tall). The latter would generally be of concern if one was prone to constantly rapping on a pier during imaging or visual work, but I suppose it could come into play if there were strong wind gusts hitting a long OTA (a non-issue in an observatory). I've used short and long OTAs on quality metal portable and permanent piers and never had a ringing issue.

I haven't studied the effects of torsional loads on an X-bar, but I also haven't seen any such problem with decent cylindrical metal piers.

Can you please point to a FEA of X-bars versus cylindrical tubes? I've used them in my lab to support micro-manipulators that work in conjunction with microscopes. I hadn't thought about using them for astronomy pier apps.




I am not aware of anyone doing any serious FEA simulations (Finite Element Analysis) of amateur-class observatory piers but there is certainly a lot of FEA that has been done in and around larger professional observatories. The results would be interesting if someone wanted to go through all of the work to create them.

An "X pier" has more surface area, no dead air spaces and a much-higher surface-area to mass ratio than a tubular or rectangular pier. This isn't likely to matter much in a lab but in an environment where there are temperature swings and you want rapid thermal stabilization, it has advantages.

Unlike research-grade microscopes or precision mechanical laboratory stages, telescope mounts carry heavy, relatively-powerful, active motor assemblies and additional components that are vulnerable to unpredictable external influences. The real challenge for telescope mounts and piers are resonant frequencies and effective damping. In the bad-old-days, this was usually solved for telescopes by lots and lots of mass (more or less.) Nowadays FEA, advanced materials and significant fundamental research have given us much-better tools to work with.

A tubular steel pier does not have near the diagonal rigidity of a steel X pier. An FEA comparison of the two would certainly show that all other things being equal, the X pier would be much more resistant to harmonic vibrations created by wind or the mount's pulsing motors running at different speeds.

And while steel is elastic and concrete effectively is not, steel has a high thermal conductivity that has benefits in an observatory when used carefully.

In "The Design and Construction of large Optical Telescopes, (c) Springer 2010", Section 6 discusses telescope mount mechanical issues at length, including the challenges and limitations of FEA simulations in the design of precision telescope support structures (mount, base & foundation.) It is an excellent reference resource for anyone desiring to build a serious, effective amateur observatory. Be warned that it is filled with math.

I hope this helps.




Thanks Chris. I'll check that book out, as it sounds interesting. I can handle math.

Edited by JJK (08/21/13 11:22 PM)


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mich_al
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Re: Pier diameter? new [Re: dmdouglass]
      #6039378 - 08/21/13 11:45 PM

FYI cement also comes in 40lb bags.

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JJK
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Re: Pier diameter? new [Re: StarmanDan]
      #6039508 - 08/22/13 02:18 AM

Quote:

Don't want to lug around hundreds of pounds of concrete mix, eh? Have you considered a concrete block pier? Mine is a little over 5' above the ground. I was considering filling the blocks with concrete but have found it is quite solid as is and was a cinch to put up and I had never worked with mortar and block construction before. I now have a very solid 16" square pier that will pretty much be able to handle anything I can put on it. All for my dinky 8" SCT.




Have you checked whether your scope will hit a 16" diameter pier?

Edited by JJK (08/22/13 02:19 AM)


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Christopher EricksonModerator
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Re: Pier diameter? new [Re: JJK]
      #6039625 - 08/22/13 06:14 AM

Quote:

Thanks Chris. I'll check that book out, as it sounds interesting. I can handle math.




Bringing up FEA's I assumed you had no problems with serious math.

That was just a heads-up for others who might not be interested in investing in an expensive book filled with dry, college-level math.

For people who consider math and engineering to be brain-candy, you'll love it.

http://www.amazon.com/Construction-Optical-Telescopes-Astronomy-Astrophysics/...


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astrodog73
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Re: Pier diameter? new [Re: JJK]
      #6039646 - 08/22/13 06:52 AM

Quote:


Have you checked whether your scope will hit a 16" diameter pier?




I was about to ask the the same.... I built a 10" pier years ago, I use an 8" newt on it now, and have to keep an eye on the mount safety limits and watch slews to the meridian carefully as it gets *very* close to the pier....


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JJK
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Re: Pier diameter? new [Re: astrodog73]
      #6039838 - 08/22/13 10:13 AM

Quote:

Quote:


Have you checked whether your scope will hit a 16" diameter pier?




I was about to ask the the same.... I built a 10" pier years ago, I use an 8" newt on it now, and have to keep an eye on the mount safety limits and watch slews to the meridian carefully as it gets *very* close to the pier....




For casual viewing in my backyard, I bolted two 4"x8" cedar beams together and used it as a pier that supported an AP900GTO mount and a few different scopes. I then widened the top of the pier by adding 3" all around (14"x14") to use an AP1200 mount and AP155 f/7. The OTA would hit the extension if I let it slew unsupervised (which I of course don't let happen).

I've seen folks add a tall, thinner "rat cages" supported by three or four 1/2" bolts atop oversized piers to make the mount level and to avoid hitting the massive pier below. Although many swear by that construction, it likely compromises the overall system's performance.

I like the X-bar concept and will look into analyzing it. I'll need a second metal pier in a few years. The X-bar is simple, can accommodate shelves and power supplies, and I might even be able to weld it myself.


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Raginar
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Re: Pier diameter? new [Re: JJK]
      #6039875 - 08/22/13 10:42 AM

Hey Dan,

How did you bolt your pier plate to that stack of bricks? Pictures?


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mclewis1
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Re: Pier diameter? new [Re: JJK]
      #6039911 - 08/22/13 11:00 AM

Like StarmanDan I used concrete blocks for at least part of my pier. I used rebar and poured concrete to further strengthen my concrete pier base. The primary benefits were how easy it was to construct. Each component was very easy to handle (individual blocks, smaller amounts of mixed concrete, etc.). The primary downside was the need for a larger hole to work in when constructing the base.

I used blocks arranged in a different manner for the first layer to provide a wider base and then simply alternated the blocks going up. Concrete between the blocks used as grout allowed for minor changes to the "trueness" of the pier base. My concrete base was about 8' tall (5' buried, 3' exposed above grade) and was done in 2 stages with rebar helping tie the two sections together.

This 16" square pier base turned out to be very solid. One minor compromise you must make with concrete block is some limitation with the placement of the J bolts (unless of course you drill them out later on). This limitation changed the original plan for the placement of the bolt holes in the base of the steel pier (and where the gussets went).

The 3' pier on top is steel and quite traditional. Folks who are concerned about ringing and overall stiffness of a steel pier should look into wall thickness. Schedule 40 pipe is very popular but the heavier schedule 80 isn't usually too much more difficult to get and makes a difference in the overall feel of the pier. It does however make the pier substantially heavier.

In my case a 10" sched 40 pier was originally planned and in the end a 8" diameter sched 80 pier was constructed. The smaller diameter pier made it a bit easier to affix reinforcing gussets to the top and bottom plates without those plates being too large. The larger the gussets the stiffer the pier will be overall. Bigger gussets starts to approach some of the benefits that Chris is describing with the X-bar pier design.

Yes less than robust "rat cages" do somewhat compromise the overall stiffness. For most folks this isn't too much of an issue. In my case I opted for a more robust "rat cage" - 4 x 3/4" diameter hardware spaced about 12" apart with 3/4" steel plate.




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Raginar
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Re: Pier diameter? new [Re: mclewis1]
      #6040376 - 08/22/13 03:45 PM

Interesting. Dan, can you post a picture of your pier?

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tomcody
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Re: Pier diameter? new [Re: dawziecat]
      #6040743 - 08/22/13 08:27 PM

Terry,
The biggest consideration is how the mount clears the pier, you don,t want to limit the mount movement with an oversize pier.
After that, height is second.
If it were me, I would use a metal pier ( I like ATS piers) as you can easily adjust ( level) if the the foundation shifts or settles.
But a properly sized concrete pier will work fine ( Dan,s piers offer good kits for concrete piers).
Rex
PS a contractor can use a powered bucket ( looks like one of those all terain fork trucks that move pallets of sod but with a tip bucket on it) to move the concrete from the truck to the build site.


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StarmanDan
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Re: Pier diameter? new [Re: Raginar]
      #6040939 - 08/22/13 10:44 PM

Quote:

Hey Dan,

How did you bolt your pier plate to that stack of bricks? Pictures?




Haven't gotten that far yet. I'm gonna try to make more progress this weekend but the plan is to stuff some newspaper in the voids of the blocks then pour concrete in just the upper block then set anchor bolts for the pier plates that the mount will bolt to. We'll see how it goes!


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JJK
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Re: Pier diameter? new [Re: StarmanDan]
      #6040963 - 08/22/13 11:03 PM

Quote:

Quote:

Hey Dan,

How did you bolt your pier plate to that stack of bricks? Pictures?




Haven't gotten that far yet. I'm gonna try to make more progress this weekend but the plan is to stuff some newspaper in the voids of the blocks then pour concrete in just the upper block then set anchor bolts for the pier plates that the mount will bolt to. We'll see how it goes!




Why not stuff the voids with broken pieces of blocks or clean stones?


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Christopher EricksonModerator
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Re: Pier diameter? new [Re: JJK]
      #6042380 - 08/23/13 07:52 PM Attachment (12 downloads)

Here is another variation on the X pier that has less mass.

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TheSheriff
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Re: Pier diameter? new [Re: JJK]
      #6042627 - 08/23/13 10:37 PM

Quote:

Quote:

Quote:

Hey Dan,

How did you bolt your pier plate to that stack of bricks? Pictures?




Haven't gotten that far yet. I'm gonna try to make more progress this weekend but the plan is to stuff some newspaper in the voids of the blocks then pour concrete in just the upper block then set anchor bolts for the pier plates that the mount will bolt to. We'll see how it goes!




Why not stuff the voids with broken pieces of blocks or clean stones?




I'm an admitted "Overkill" type, but after all that work, why not just fill the entire void with concrete? Or at least, fill all but the top foot with damp sand and crete the remainder.


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roscoe
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Re: Pier diameter? new [Re: TheSheriff]
      #6043159 - 08/24/13 08:37 AM

Chris,
Looking at your latest sketch reminded me of the look of a z-braced radio tower - how well do you think a short section of something like Rohn 25 would work as a pier top?
Russ


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dawziecat
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Re: Pier diameter? new [Re: tomcody]
      #6043203 - 08/24/13 09:12 AM Attachment (6 downloads)

Quote:

If it were me, I would use a metal pier ( I like ATS piers) as you can easily adjust ( level) if the the foundation shifts or settles.
But a properly sized concrete pier will work fine ( Dan,s piers offer good kits for concrete piers).
Rex




Many thanks for the tip on Dan's Piers, Rex. I had not heard of them.

I have found a contractor to do the concrete work. Furthermore, he says he can get his 4X4 into the site on the very rough track the excavator has made. It just may be necessary the excavator haul the truck back out!

The budget will not allow one of those very fine ATS piers.

So I plan on a 12" concrete pier, topped by a plate from Dan's Piers that will directly accept the Astrophysics 119FSA adapter for the AP1100.


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Midnight Dan
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Re: Pier diameter? new [Re: dawziecat]
      #6043281 - 08/24/13 10:14 AM

Good plan! I think that should work well for you. Don't forget the rebar in the concrete. 2 pieces should be plenty, but many people use 3.

-Dan


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dawziecat
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Re: Pier diameter? new [Re: Midnight Dan]
      #6043329 - 08/24/13 10:40 AM

Quote:

Good plan! I think that should work well for you. Don't forget the rebar in the concrete. 2 pieces should be plenty, but many people use 3.

-Dan




Hmmm . . . is rebar really necessary?


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Midnight Dan
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Re: Pier diameter? new [Re: dawziecat]
      #6043352 - 08/24/13 10:49 AM

Absolutely! Concrete is extremely strong in compression so rebar will not help one bit in supporting the weight of your gear. But, it is very weak in tension or shear, which means it can easily break due to relatively small sideways forces such as movement of the ground in freeze-thaw cycles.

-Dan


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dawziecat
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Re: Pier diameter? new [Re: Midnight Dan]
      #6043384 - 08/24/13 11:10 AM

Quote:

Good plan! I think that should work well for you. Don't forget the rebar in the concrete. 2 pieces should be plenty, but many people use 3.

-Dan




Hmmm . . . is rebar really necessary? I hadn't planned on it. I don't want to mess with the stuff unless I really have to!
I read all about it adding strength against shearing forces but they're not really a concern. All I see rebar doing is getting in the way of properly seating the L bolts and allowing voids to form in the concrete?


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dawziecat
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Re: Pier diameter? new [Re: dawziecat]
      #6043394 - 08/24/13 11:16 AM

Whoops . . . sort of a double posting done inadvertently.

Thanks Dan, I guess a couple lengths of rebar will be necessary. Not happy about it but . . .


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tim57064
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Re: Pier diameter? new [Re: dawziecat]
      #6043554 - 08/24/13 12:46 PM

If you do not use rebar,it will not be long before the pier breaks apart.It is not that expensive here yet not sure where you are located.I am sure though that it would be more expensive to replace the pier.

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mclewis1
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Re: Pier diameter? new [Re: tim57064]
      #6043602 - 08/24/13 01:14 PM

Terry,

I'd use 3 pieces of rebar with some thin wire between the pieces to hold it in shape. Size the rebar length to go down into the base and up to a point just below the top surface. You shouldn't have any problem keeping it away from the sides or the points where you want your J bars. You'll also be able to use a long pole (broom handle or similar) down the middle of the rebar to help prevent any voids as you're pouring the concrete.

A slightly wetter mix (think runny but lumpy oatmeal) will also make the pour around the rebar and tamping to remove voids easier.


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Midnight Dan
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Re: Pier diameter? new [Re: dawziecat]
      #6043647 - 08/24/13 01:43 PM

Quote:

... I guess a couple lengths of rebar will be necessary. Not happy about it but . . .




I think when you're done you'll find that the rebar was not a big deal at all compared to everything else. It's cheap, and easy to work with. Just buy some cheap steel wire to wrap around it hold it in the shape you want. It doesn't have to be fancy or pretty - it will be hidden inside the concrete.

For mine, I just used two pieces wired together like the photo below. Seems like most people in the threads here on CN use 3 pieces. Either way, it's probably the least of your worries when building an observatory.

I think the slightly running mix suggested above is a good idea. Mine was pretty stiff and I ended up with some small voids on the side - nothing that's a real problem, but it just didn't look as good as I'd like. Be SURE and agitate the concrete to help it flows everywhere in the form and helps to eliminate voids. I used another length of rebar to run it up and down in the mix and also side to side. I'd stop to agitate about every quarter of the pour.



-Dan


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HunterofPhotons
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Re: Pier diameter? new [Re: tim57064]
      #6043650 - 08/24/13 01:43 PM

Quote:

If you do not use rebar,it will not be long before the pier breaks apart.....




OMG!!!!!!
When I think of all the concrete columns that I've poured without rebar it just makes me sick. I've left so many people with ticking time bombs.
Admittedly none of these columns have broken apart yet (even afters decades of use), but oh the humanity when they do shatter and collapse.

Concrete columns have been around for thousands of years.
I don't know of any that had rebar yet they are still standing.
The tension forces on our astronomical columns are virtually non-existent for all practical purposes. There is no need for rebar from that quarter.
Are there any situations where rebar may be needed?
The only one that comes to mind is if you have built your observatory on steeply sloping land that suffers from severe frost in the winter. In that instance rebar may save your pier from coming apart. It won't save it from being pushed out of plumb, but at least it will be in one piece.
Other than that you don't need rebar.
The ironic thing is that most of the rebar installations that I have seen in observatory forums are incorrect and they are causing problems rather than preventing them. They pound the rebar into the ground and pour on top of that. Rebar needs to be totally encased in concrete. When rebar gets wet, like from goundwater, it rusts and expands.
Guess what happens to the concrete. It splits open.

dan k.


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Christopher EricksonModerator
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Re: Pier diameter? new [Re: roscoe]
      #6043680 - 08/24/13 01:57 PM

Quote:

Chris,
Looking at your latest sketch reminded me of the look of a z-braced radio tower - how well do you think a short section of something like Rohn 25 would work as a pier top?
Russ




Rohn tower segments are designed to be ultra-light and a bit flexible for survivability in wind. My instincts say that they would be vulnerable to higher-frequency (50-500hz) sympathetic vibrations but that's only a guess.

The self-supporting Rohn tower segments would be a bit better than the guyed-tower segments.


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Mary B
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Re: Pier diameter? new [Re: Christopher Erickson]
      #6043749 - 08/24/13 02:37 PM

I had 30 feet of rohn 25 bracketed to the house. Talk about resonate and howl in the wind!!!

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rimcrazy
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Re: Pier diameter? new [Re: dawziecat]
      #6044797 - 08/25/13 08:39 AM

I've posted pic's of this before. My pier is 10' high from concrete base to the top. 8' from the level of the floor. It sits on over 12,000 lbs of concrete on a 5x5x3 block with a 2'x2' round pier in the center. The second level up bolts to the concrete pier at the floor level with 8 bolts. There are 12 bolts that anchor the pier to the concrete at the bottom. Bolting the mid level up loads the beams to put tension on them to reduce vibration. The asymmetric design reduces/eliminates harmonic ringing. Using steel allows for rapid cooling and reaching thermal equilibrium.

Having to go 4' down is a bit tough for getting below the frost line. Mine is only 18" down which makes it much easier. Chris's X-Design is quite robust and would do a very good job for you. Obviously, you either need to be able to do the steel work yourself or have access to someone that can do that work for you.

Here is the CAD design:



I have a top plate adapter. This is a 1/2" plate steel waterjet cut from a CAD drawing. The large holes bolt the plate flush down to the top of the pier. The smaller holes are all tapped. Cost of the plate including waterjet was $90



It's designed to fit a Meade LX200 wedge and a AP1600GTO Flat surface adapter. The wedge is gone and I'm waiting for the AP1600 to be delivered. I don't see the need at all for level adjusting. It's not required and IMHO reduces the rigidity of the overall mount. My concrete was poured very level and the pier is quite square. After 10' you can see that the top wedge is only slightly off level.



Again, level is not required. What is required is accurate polar alignment.

Finished pier





Hopefully this gives you some ideas for what you might want to do.


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Midnight Dan
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Re: Pier diameter? new [Re: HunterofPhotons]
      #6044909 - 08/25/13 10:17 AM

Quote:

OMG!!!!!! When I think of all the concrete columns that I've poured without rebar it just makes me sick ... oh the humanity when they do shatter and collapse ...

The tension forces on our astronomical columns are virtually non-existent for all practical purposes. There is no need for rebar from that quarter.




Sarcasm aside, tension definitely exists in-ground pier. It comes from two sources. The first is any sideways motion of the ground. When any thick object like a pier experiences a lateral force, the side away from the force is in compression while the side nearest the force is in tension.

Think the ground is stationary? Take a look at any farm fence built of wood poles stuck in the ground. If it's been there for more than a few years, the poles lean every which way due to to heavy rains, soil migration and settling (especially on sloping sites), and frost heaves. And that brings up the second tension force - frost heaves.

Frost heaves occur when the ground is saturated with water near the surface and then freezes. Since water expands when it freezes, it grips objects like piers tightly and then lifts them upward, again due to the expansion. This uplift force is one reason why its a good idea for the bottom of the pier, under the frost line, to be larger than the rest - to resist the uplift force and keep the pier in the ground. However, if you have a footer keeping the bottom stationary, and a frost heave trying to lift the top, you have - wait for it - tension!

Since the OP is in Nova Scotia, frost heaves area a very real concern and rebar in the concrete will eliminate that concern. Your experience with columns brings to mind the mind the old saying - just because something has been done and not failed, doesn't make it a good design. Will it fail if rebar is not used? Perhaps not. But putting rebar in is easy ... replacing a broken pier is not. Just my 2 cents, but I would not put in a pier without rebar.

-Dan


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HunterofPhotons
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Re: Pier diameter? new [Re: Midnight Dan]
      #6045043 - 08/25/13 11:44 AM

Just out of curiosity, how many mount piers have you seen pulled apart by frost heaves?

dan k.


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Christopher EricksonModerator
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Re: Pier diameter? new [Re: rimcrazy]
      #6045125 - 08/25/13 12:45 PM

Excellent design!

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TimN
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Re: Pier diameter? new [Re: Christopher Erickson]
      #6045303 - 08/25/13 02:29 PM

I can't comment on other climates but the OP has a similar climate as mine. Concrete columns are used a lot for cottage supports etc. in my area and all installations follow 3 rules. 1. Go below frost line 2. Larger at the bottom 3. Use rebar.
The only exception on depth is when you connect to bedrock and even then you use rebar.

Soil and other conditions may mean all these steps aren't necessary but why take a chance with your pier? Rebar is so inexpensive and easy to install.


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Midnight Dan
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Re: Pier diameter? new [Re: HunterofPhotons]
      #6045381 - 08/25/13 03:06 PM

Quote:

Just out of curiosity, how many mount piers have you seen pulled apart by frost heaves?

dan k.




None. The few piers I've seen have all had rebar in them and have not been pulled apart by frost heaves or any other reason.

-Dan


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roscoe
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Re: Pier diameter? new [Re: Midnight Dan]
      #6046157 - 08/25/13 11:01 PM

Quote:

Quote:

Just out of curiosity, how many mount piers have you seen pulled apart by frost heaves?

dan k.





I'm a small-town contractor/carpenter, and I've seen quite a few that have pulled apart from frost action - mostly foundation piers under porches and decks. They normally seem to break about 6" below the ground surface, or near the bottom of a j-bolt or short piece of rebar put in to attach a post anchor to.

On the other hand, an 8" pier with a single 1/2" re-bar in it can be cracked, but cannot be broken fully or pulled apart, even if slammed with the bucket of a backhoe in an attempt to break it into pieces for removal. With 2 re-bars, they're hard to even crack, and must be in both cases dug up whole.

While they're not quite as rust-resistant or strong, I often use lengths of threaded rod for re-enforcement, because they serve both strength and anchor purposes at once.
Russ


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dawziecat
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Re: Pier diameter? new [Re: roscoe]
      #6046540 - 08/26/13 08:35 AM

I have ordered the top plate from Dan's Piers but I can not wait for delivery of the stainless steel L bolts. They are not available locally either. Dan suggested SS threaded rod with a couple of nuts on the end instead. My contractor suggested bending them but how can I bend 3/4" rod?

Another possibility are galvanized L bolts.

So, options are:

1/ SS threaded rod with nuts.
2/ SS rod "home bent" into an L shape (if possible!)
3/ Galvanized L bolts

Opinions?


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Midnight Dan
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Re: Pier diameter? new [Re: dawziecat]
      #6046566 - 08/26/13 08:56 AM

Hi Terry:

You can get the stainless L-bolts at McMaster-Carr here:
http://www.mcmaster.com/#l-bolts/=o8ciz1
BUT ... they are more expensive than the kit from Dan's. You might get away cheaper by asking Dan to overnight his kit to you. He includes the thin-profile jam nuts, stainless washers, and fiber washers that work well for attaching a mount.

Keep in mind that a normal L-bolt is designed to hold something, like a house foundation, tightly to the concrete. The force of the nut tightened against the foundation attempts to pull the bolt out of the concrete, so the "L" part is necessary to resist that pull.

However, your mount is a totally different situation. Most people suspend the mount above the concrete between two nuts on the threads. There is ZERO force trying to pull the bolt out of the concrete. In fact, just the opposite is true - the weight of the mount and optical gear are trying to push the bolts INTO the concrete. An "L" at the end can help a little by spreading out that weight, but it isn't really needed. Concrete is so strong in compression that a simple piece of threaded rod should work fine.

If you want to bend the end yourself, it should be easy to do. Just clamp the rod in a vice and beat on the end with a hammer, or use a pipe wrench to grab and bend the end. It doesn't have to be a 90° bend and it doesn't have to be pretty.

Personally, I'd stick with stainless instead of galvanized. The thread will be smoother which makes it easier to adjust the mount to level. Not sure about other brands, like the McMaster-Carr ones, but in the kit I got from Dan's Pier Plates, the bolts were amazing well made - more like fine machining than the normal crude bolts I'm used to seeing for foundation work.

-Dan


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Midnight Dan
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Re: Pier diameter? new [Re: Midnight Dan]
      #6046580 - 08/26/13 09:05 AM

Just a reference regarding frost heaves and rebar in piers:

http://www.structuretech1.com/2013/06/frost-heave-and-deck-footings/

The whole thing is pretty short and can be read quickly. But to get to the pertinent information, scroll down to the bottom and read the two paragraphs between the image of the sonotube with the concrete bell-bottom, and the drawing of the pier with rebar in it.

-Dan


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rimcrazy
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Re: Pier diameter? new [Re: Midnight Dan]
      #6046593 - 08/26/13 09:14 AM

Just a quick note. If you use SS bolts, be sure you don't use SS nuts, or if you do remember to put anti-seize on the threads.

You can get locking threaded inserts that you simply put into a drilled hole in concrete. This is what I did on my pier. I had lots of bolts to put in (20) and there is no way you can locate that many bolts accurately to holes in the steel. We simply put the pier down, drilled the holes with an industrial drill, put in the threaded inserts and screwed bolts into the inserts. In our case, to be sure, we put a special concrete epoxy into the holes to be sure nothing came out. Probably unnecessary but there is no way the bolts are coming out.


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dawziecat
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Re: Pier diameter? new [Re: rimcrazy]
      #6046653 - 08/26/13 09:59 AM

Please don't forget that I am in a third world country! Sometimes that's how I feel about Canada! Getting things shipped here from the US is slow and prohibitively costly. And that's when the merchants agree to ship to Canada at all, and they often don't!

The industrial supplier here informs me I have virtually no chance of obtaining SS L bolts here! And I can't wait for all the delays of having them shipped to Canada from the US. If I could, I'd just order 'em from Dan's.

Now, what's this about not using SS bolts on SS rod lest they seize? Please tell me more about that. I've heard of Loctite, but never an "anti-seize" compound. Teflon tape? Plumber's joint compound?

PS: I have ordered the SS L bolts from McMaster-Carr. We'll see what happens.
Thanks for that link, Dan.

Edited by dawziecat (08/26/13 10:22 AM)


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rimcrazy
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Re: Pier diameter? new [Re: dawziecat]
      #6046833 - 08/26/13 11:40 AM

If you put a SS bolt with a SS nut and you do not use an anti-seize compound you get what acts like welding of the nut to the bolt. It's not really a weld per se but the metal is soft enough that the heat generated by screwing a nut on to a bolt will cause spalling at the surface which, for all intent and purpose, is a weld.



I neglected to do this or rather did not realize the nut I was using (came from the proverbial collection of random nuts in a jar in the shop) was SS and I did not use anti-seize. You can see how far the nut got on to the bolt before it totally seized up. I needed an 18" breaker bar with a pipe to get it off... or rather snap the bolt in this case. I keep this on the mount to remind me of my stupidity.

The simplest way around this is just use anodized or zinc coated nuts if you use SS bolts. The same goes for vice-versa. If you have SS nuts just be sure to use anodized or zinc coated bolts and you won't have a problem. This also happens with aluminum to aluminum bolts and nuts, etc.


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dawziecat
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Re: Pier diameter? new [Re: rimcrazy]
      #6046967 - 08/26/13 12:57 PM

Thanks for that Rimcrazy. I'll be sure it doesn't happen.

McMaster-Carr cancelled my order to Canada.
What I don't understand is why they offer drop-down menus to select other countries in the first place when they won't accept orders from anything but the US?

I think I'll move to Botswana!

Edited by dawziecat (08/26/13 12:59 PM)


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roscoe
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Re: Pier diameter? new [Re: Midnight Dan]
      #6046978 - 08/26/13 01:03 PM

Quote:

Just a reference regarding frost heaves and rebar in piers:

http://www.structuretech1.com/2013/06/frost-heave-and-deck-footings/

The whole thing is pretty short and can be read quickly. But to get to the pertinent information, scroll down to the bottom and read the two paragraphs between the image of the sonotube with the concrete bell-bottom, and the drawing of the pier with rebar in it.

-Dan




An excellent description of the situation!

And....frozen ground will lift EVERYTHING! .....like my Buddy's large bulldozer parked on a concrete slab for the winter, for instance.....

This is something to consider for those who build observatories on foundation blocks on the ground, and piers below frost line.... the building will move while the pier stays in place.

Russ


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tomcody
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Re: Pier diameter? new [Re: dawziecat]
      #6047063 - 08/26/13 02:10 PM

Terry.
ATS uses 3/4" SS all thread rod for their J bolts, they use a straight length of rod and weld a section of the same rod about 2" long at the bottom to form an L shape. (if you have a welder available? may be faster?)
Rex


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Midnight Dan
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Re: Pier diameter? new [Re: roscoe]
      #6047066 - 08/26/13 02:11 PM

Quote:

McMaster-Carr cancelled my order to Canada.




Yeesh! You can't catch a break.

Here's a good article on the potential of galling when using stainless on stainless:
http://www.estainlesssteel.com/gallingofstainless.html

I use "Never-Sieze" brand anti-sieze lubricant in situations like this, but according to the article, there are lots of good greases that will work just as well.

-Dan


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dawziecat
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Re: Pier diameter? new [Re: Midnight Dan]
      #6047137 - 08/26/13 02:45 PM

"Never-Sieze" is probably something else I can't get in Canada!

I'll use non SS bolts.

Now I need a welder!

Good grief. This whole pier thing is turning into a nightmare! Between international border complications and metallurgical spalling catastrophes, not to mention proper rebar technique, it's enough to make me "rend my garments!"


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Christopher EricksonModerator
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Re: Pier diameter? new [Re: dawziecat]
      #6047156 - 08/26/13 02:54 PM

Skyshed is in Canada and has lots of the things you might need.

http://www.skyshed.com/


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tomcody
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Re: Pier diameter? new [Re: dawziecat]
      #6047298 - 08/26/13 04:31 PM

Never seize or a simular anti- seize compound is sold at all hardware and
auto parts stores. its used for preventing bolts on car engines from seizing.
Rex


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dawziecat
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Re: Pier diameter? new [Re: tomcody]
      #6047366 - 08/26/13 05:19 PM

Quote:

Never seize or a simular anti- seize compound is sold at all hardware and
auto parts stores. its used for preventing bolts on car engines from seizing.
Rex




Thanks, Rex. I'll try the local NAPA.


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Midnight Dan
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Re: Pier diameter? new [Re: dawziecat]
      #6047373 - 08/26/13 05:24 PM

They should have something. Again, the article says any decent Moly grease will work too. If you can't find Moly grease ... well, then you're in a 4th world country!

-Dan


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Raginar
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Re: Pier diameter? new [Re: Midnight Dan]
      #6047386 - 08/26/13 05:29 PM

Dan, you get the top of your pier done yet?

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Midnight Dan
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Re: Pier diameter? new [Re: Raginar]
      #6047395 - 08/26/13 05:38 PM

Hi Chris:

If by the "top of the pier" you mean the observatory, then no. I'm still waiting for the POD to ship. Did you mean something else? The pier has been done for quite a while now.

-Dan


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Christopher EricksonModerator
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Re: Pier diameter? new [Re: Midnight Dan]
      #6047538 - 08/26/13 07:07 PM

Quote:

Hi Chris:

If by the "top of the pier" you mean the observatory, then no. I'm still waiting for the POD to ship. Did you mean something else? The pier has been done for quite a while now.

-Dan




I was simply referring to pier parts.

Also, Break-Free CLP is a great anti-seizing lubricant.


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TimN
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Re: Pier diameter? new [Re: Christopher Erickson]
      #6047546 - 08/26/13 07:14 PM

I probably missed something obvious Terry but why can't you just use J bolts - the kind you get at any hardware store.

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Midnight Dan
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Re: Pier diameter? new [Re: TimN]
      #6047569 - 08/26/13 07:28 PM

Quote:

I was simply referring to pier parts.




In that case yes, it's done:



-Dan


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dawziecat
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Re: Pier diameter? new [Re: TimN]
      #6047653 - 08/26/13 08:29 PM

Quote:

I probably missed something obvious Terry but why can't you just use J bolts - the kind you get at any hardware store.




Hi Tim:

Twelve inch X 3/4 inch stainless steel J-bolts?
Not likely in any hardware store in Nova Scotia.
Galvanized maybe.

If you know anyone within Canada who will ship that size SS J-bolt to me, please let me know.


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mclewis1
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Re: Pier diameter? new [Re: dawziecat]
      #6047762 - 08/26/13 09:33 PM

3/4" SS J bolts are indeed difficult to find locally. I went slightly smaller and didn't even bother to go galvanized. After they're installed and an observatory is raised they'll never be wet again. Mine are covered by a removable part of my decking.

I used 3/4" SS hardware for the rat cage area. It is a much more visible area, plus it's easier to get than the J bolts ... 3/4" threaded rod is quite popular in local hardware stores.

Anti seize is available in most Canadian tire stores - look up Permatex Copper Anti-Seize


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TheSheriff
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Re: Pier diameter? new [Re: mclewis1]
      #6048057 - 08/27/13 12:46 AM

Quote:

3/4" SS J bolts are indeed difficult to find locally. I went slightly smaller and didn't even bother to go galvanized. After they're installed and an observatory is raised they'll never be wet again.




My thoughts exactly. Use SS for the bling factor or some extreme environmental condition, like on Jupiter. I used 3/4 galvanized threaded rod with a welded anti-rotational tab on the end. It will outlast my grand daughter's children.


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dawziecat
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Re: Pier diameter? new [Re: TheSheriff]
      #6048288 - 08/27/13 07:37 AM

Anyone have any suggestions as to an anti-rotation tab that I could afix to the end without welding, like with nuts. I plan to use a washer 2" in diameter between two nuts but that isn't much to prevent the rod rotating within the concrete.

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TimN
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Re: Pier diameter? new [Re: dawziecat]
      #6048431 - 08/27/13 09:20 AM

Terry, I'm with Mark and Brad and just used local stuff. Galvanized J Bolts for the bottom and SS for rats cage. Should all be easy to get locally. Don't make things too hard - they are already hard enough.

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JJK
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Re: Pier diameter? new [Re: TimN]
      #6048490 - 08/27/13 09:56 AM

I used galvanized bolts bent into Ls and haven't had a problem.

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dawziecat
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Re: Pier diameter? new [Re: mclewis1]
      #6048497 - 08/27/13 10:00 AM

Quote:

I went slightly smaller and didn't even bother to go galvanized. Mine are covered by a removable part of my decking.

I used 3/4" SS hardware for the rat cage area.





Hi Mark:

Your post confuses me a bit. It seems to describe a metal pier affixed to concrete at or below floor level? But then you have a rat's cage too? Why would you need a rat's cage if the pier can be leveled by shimming the pier base?

I plan a concrete pier with a rat's cage for leveling. So, the only metal fasteners are at the top. Nothing at/below floor level.

I plan to go to Dartmouth tomorrow to TransWorld , apparently THE place for fasteners in this neck of the woods.

I see on their site they have SS "anchor bolts!" I called and asked for SS "L-bolts" and they blew me off.
Looks like they may have SS steel L- bolts after all. They just don't call 'em that.

Edited by dawziecat (08/27/13 10:14 AM)


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mclewis1
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Re: Pier diameter? new [Re: dawziecat]
      #6048627 - 08/27/13 11:20 AM

Terry,

While shimming the base between the steel and concrete sections would indeed allow me some flexibility it wasn't enough to make larger changes to the overall height I expected to need, plus the steel pier is really heavy and I had no intention of ever futzing with the base of it. The addition of a nice robust "rat cage" made more sense for me. Plus it also gives me a nice place to store USB hubs, etc. and other bits and pieces.

Another option if you can't get SS L/J/anchor bolts is to simply use a SS threaded rod cut long and then add some plain nuts and a 2" fender washer. That will provide enough surface area to solidly hold them when embedded into the concrete. Just watch how close to the edge the washers end up (depends on the diameter of the concrete pier) ... if it's too close smaller washers can be used. I might also stagger the height of the washers/rods to ensure that there isn't a substantially weaker layer at the point of all three washers.

Since you are going to use the anchor bolts set in concrete to affix your top plate I'd suggest when setting the anchor bolts to use a good solid piece of wood accurately drilled for your bolt pattern (or the actual top plate if you have it) with each anchor bolt installed and with nuts to solidly attach each bolt to it. Don't try to place each bolt separately in the wet cement and then use the wood template to bring them into alignment. Putting all the bolts on the wood template and dry fitting them also ensures that there are not any "close" situations (where you feel you can just nudge the bolt into position). You really don't want one of these bolts to be even slightly off from vertical or horizontally out of position.

Edited by mclewis1 (08/27/13 12:08 PM)


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Midnight Dan
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Re: Pier diameter? new [Re: mclewis1]
      #6048649 - 08/27/13 11:39 AM

Hi Terry:

Mark brings up a good point about putting the bolts in the concrete. I used a 2-layer wood form to keep the bolts precisely straight, but I'm sure I went a bit overboard. I think most people just use a single layer of heavy plywood and a couple of nuts on each bolt to clamp it to the wood.

Here's my setup:




-Dan


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dawziecat
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Re: Pier diameter? new [Re: mclewis1]
      #6048699 - 08/27/13 12:12 PM

Many thanks, Mark.

I plan on using a 1.5" thick plywood template. Am sweating bullets trying to ensure it is accurate as I will not likely have the actual top plate in hand when the concrete is placed. I won't be trying to "wiggle" the individual rods about in wet concrete. I appreciate they must be accurate and vertical.


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roscoe
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Re: Pier diameter? new [Re: dawziecat]
      #6049392 - 08/27/13 06:12 PM

Quote:

Anyone have any suggestions as to an anti-rotation tab that I could afix to the end without welding, like with nuts. I plan to use a washer 2" in diameter between two nuts but that isn't much to prevent the rod rotating within the concrete.





I'm perhaps confused, but are you talking about threaded rods here? If so, the concrete will stick to them enough that they won't ever turn, if you have a couple of locked together hex-nuts on them, you're doubly protected, if you want, you can bend then just slightly, and you'll be triple-safe.
Jiggle them around a bit as you install them in the concrete or the concrete around them, that action will work the finer particles in the mix into the threads, insuring a truly solid bond.

And, in case nobody's mentioned it in a week or two, vigorously working a rod or stick up and down in the concrete as you fill your tube will break up air bubbles or let them rise to the surface, and will work fines out against the sides of the form. tapping the sides of the form with a piece of wood (like a foot-long hunk of 2x4) also makes for a nicer-looking final product.
R


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JJK
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Re: Pier diameter? new [Re: dawziecat]
      #6049620 - 08/27/13 08:32 PM

Quote:

Quote:

I went slightly smaller and didn't even bother to go galvanized. Mine are covered by a removable part of my decking.

I used 3/4" SS hardware for the rat cage area.





Hi Mark:

Your post confuses me a bit. It seems to describe a metal pier affixed to concrete at or below floor level? But then you have a rat's cage too? Why would you need a rat's cage if the pier can be leveled by shimming the pier base?

I plan a concrete pier with a rat's cage for leveling. So, the only metal fasteners are at the top. Nothing at/below floor level.

I plan to go to Dartmouth tomorrow to TransWorld , apparently THE place for fasteners in this neck of the woods.

I see on their site they have SS "anchor bolts!" I called and asked for SS "L-bolts" and they blew me off.
Looks like they may have SS steel L- bolts after all. They just don't call 'em that.




Why bother with a rat cage at all?


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dawziecat
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Re: Pier diameter? new [Re: JJK]
      #6050207 - 08/28/13 08:21 AM

Quote:

Why bother with a rat cage at all?




Seems to me there are only two ways to do this, with a third that is "maybe."

1/ Metal pier with provision for leveling at the pier base.
2/ Concrete pier with provision for leveling via a "rat cage."
3/ Maybe, just maybe your concrete surface at the pier top is perfectly level and finished smoothly enough that a top plate can be affixed flush to it and bolted tightly to the concrete surface.

As I see it:

Number one is just too expensive . . .for me anyway. Cost of a 10" ATS pier delivered in Canada would be in excess of 2300 USD plus 15%HST. Only Canadians are likely to understand that the costs will probably be pushing $3,000 CDN by the time this thing actually showed up here. That is $3,000 in addition to the concrete costs for the base!

Number two is very cost effective. The rat cage seems robust enough to me with a trio of 3/4" stainless steel bolts bearing the weight and allowing for precise and easy leveling.

Number three is . . . . maybe. I hope to have the threaded portion of the bolts extend into the concrete so that this option will remain open. Whether I use it or not will depend on how smoothly finished and level I can get the top surface.


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TimN
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Re: Pier diameter? new [Re: dawziecat]
      #6050537 - 08/28/13 11:47 AM

I agree your number 2 is cheaper but you can get a metal pier just over 8.5" to fit on a 14" concrete tube for $800 Cdn from Skyshed here in Canada that should be good up to about a 14" scope.

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Footbag
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Re: Pier diameter? new [Re: dawziecat]
      #6050724 - 08/28/13 01:35 PM

Quote:

Many thanks, Mark.

I plan on using a 1.5" thick plywood template. Am sweating bullets trying to ensure it is accurate as I will not likely have the actual top plate in hand when the concrete is placed. I won't be trying to "wiggle" the individual rods about in wet concrete. I appreciate they must be accurate and vertical.




I waited until I got my top plate before pouring the final pier pour. It was a good thing I did because the template I made for the bolts held them slightly crooked. Fortunately I checked to ensure the top plate fit the bolts after the pour.

With a thick enough template board, it won't be an issue, but make sure you get it right. Personally, I'm glad I waited. You have about 10m to get it right.


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Midnight Dan
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Re: Pier diameter? new [Re: Footbag]
      #6050739 - 08/28/13 01:44 PM

Quote:

I waited until I got my top plate before pouring the final pier pour. It was a good thing I did ...




Good advice! I did that too. I used the top plate as a template for drilling the wood piece so I would be sure it was correct.

-Dan


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Raginar
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Re: Pier diameter? new [Re: Midnight Dan]
      #6050827 - 08/28/13 02:28 PM

Dan, can you detail how you did the top of your brick pier?

Pictures?


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dawziecat
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Re: Pier diameter? new [Re: Midnight Dan]
      #6050904 - 08/28/13 03:27 PM

Quote:

I waited until I got my top plate before pouring the final pier pour. It was a good thing I did ...




Can't do it! I just have to procede before Dan's can deliver the plate! To do otherwise likely means no pier at all or extra costs to have the hole excavated next summer. Means no progress at all this season. I'd like to have the pier ready for the 1100 mount which AP tells me will be delivered in November. I'll do what I can to ensure I have the bolts in the correct position and vertical. I'd absolutely hate to enlarge the holes in the top plate but if it comes to that, it will just have to be done!

The shop in Dartmouth will fabricate a set of three 12"X3/4"L bolts in stainless steel, complete with two nuts and two washers apiece for $59 each. Not really much more than I was going to have to pay McMaster-Carr before they cancelled the order.


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Midnight Dan
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Re: Pier diameter? new [Re: Raginar]
      #6050905 - 08/28/13 03:27 PM

Hi Chris:

I think you have me mixed up with someone else - maybe StarmanDan? Photos of my pier are in the thread above. It's poured concrete, not made of bricks.

-Dan


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Midnight Dan
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Re: Pier diameter? new [Re: Midnight Dan]
      #6050938 - 08/28/13 03:45 PM

Quote:

I'd absolutely hate to enlarge the holes in the top plate but if it comes to that, it will just have to be done!




I think you'll be fine. If you look at the Dan's Pier Plate site, the bottom part of the plate has curved, slotted holes for the anchor bolts. So if you're off a little, there's some room for adjustment.

-Dan


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Raginar
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Re: Pier diameter? new [Re: Midnight Dan]
      #6050963 - 08/28/13 04:09 PM

Yea I do, sorry

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rimcrazy
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Re: Pier diameter? new [Re: dawziecat]
      #6051035 - 08/28/13 04:44 PM

Quote:

I'd like to have the pier ready for the 1100 mount which AP tells me will be delivered in November.




You can't help but love AP's quality but.... My 1600 was suppose to be delivered in July. Now they are telling me early Sept. We shall see. I know it will be perfect when I get it but don't hold your breath on getting your 1100 in Nov.


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dawziecat
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Reged: 10/20/10

Loc: Rural Nova Scotia
Re: Pier diameter? new [Re: rimcrazy]
      #6051267 - 08/28/13 06:45 PM

Quote:


You can't help but love AP's quality but.... My 1600 was suppose to be delivered in July. Now they are telling me early Sept. We shall see. I know it will be perfect when I get it but don't hold your breath on getting your 1100 in Nov.




My understanding is, once they take your money, and they just took $4,600 of mine 48 hours ago, their delivery dates are pretty reliable?


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Pier diameter? new [Re: dawziecat]
      #6051309 - 08/28/13 07:06 PM

Quote:

Quote:

Why bother with a rat cage at all?




Seems to me there are only two ways to do this, with a third that is "maybe."

1/ Metal pier with provision for leveling at the pier base.
2/ Concrete pier with provision for leveling via a "rat cage."
3/ Maybe, just maybe your concrete surface at the pier top is perfectly level and finished smoothly enough that a top plate can be affixed flush to it and bolted tightly to the concrete surface.

As I see it:

Number one is just too expensive . . .for me anyway. Cost of a 10" ATS pier delivered in Canada would be in excess of 2300 USD plus 15%HST. Only Canadians are likely to understand that the costs will probably be pushing $3,000 CDN by the time this thing actually showed up here. That is $3,000 in addition to the concrete costs for the base!

Number two is very cost effective. The rat cage seems robust enough to me with a trio of 3/4" stainless steel bolts bearing the weight and allowing for precise and easy leveling.

Number three is . . . . maybe. I hope to have the threaded portion of the bolts extend into the concrete so that this option will remain open. Whether I use it or not will depend on how smoothly finished and level I can get the top surface.




If you make your concrete pier the height you need, I see no reason for the rat cage. If the concrete pier top is not quite level, you can use a metal shim.


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rimcrazy
sage


Reged: 03/03/12

Loc: Overgaard, AZ
Re: Pier diameter? new [Re: dawziecat]
      #6051421 - 08/28/13 08:08 PM

Well I put 50% down in June and was told then delivery in July. They will bill the other half I'm sure just before they ship so if u just paid the second half they'll should ship soon. If u just paid the first half down then its just a guess. They have shipped early at times but I suspect if u search the forum you will find they are often a bit late. They don't hide this and in fact clearly say so on their web site. I knew that before I purchased my mount as I said too their quality is unsurpassed so its worth the wait but if you were expecting a precise shipment you will probably be disappointed.

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Footbag
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Re: Pier diameter? new [Re: rimcrazy]
      #6051471 - 08/28/13 08:45 PM

I don't consider the three L-anchor bolts a ratcage. The concrete side is anchored for a long length of the bolt and mine only rise 3 1/2" from the concrete.

After looking at piers and ratcage designs, I decided the concrete pier with a Dans Pier plate was the easiest and cheapest. 3/4" bolts
cannot flex that much in 3".


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Pier diameter? new [Re: Footbag]
      #6051551 - 08/28/13 09:46 PM

Quote:

I don't consider the three L-anchor bolts a ratcage. The concrete side is anchored for a long length of the bolt and mine only rise 3 1/2" from the concrete.

After looking at piers and ratcage designs, I decided the concrete pier with a Dans Pier plate was the easiest and cheapest. 3/4" bolts
cannot flex that much in 3".




I just don't see the point in depending on that assumption .


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Footbag
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Re: Pier diameter? new [Re: JJK]
      #6051625 - 08/28/13 10:41 PM

Quote:

Quote:

I don't consider the three L-anchor bolts a ratcage. The concrete side is anchored for a long length of the bolt and mine only rise 3 1/2" from the concrete.

After looking at piers and ratcage designs, I decided the concrete pier with a Dans Pier plate was the easiest and cheapest. 3/4" bolts
cannot flex that much in 3".




I just don't see the point in depending on that assumption .




I have seen 4-bolt designs with large "ratcages", but with these, the bolts are bolted on both sides and are much longer. By having the L-anchor bolts embedded in concrete and keeping them shorter, you are limiting the risk of flex or vibration. By using 3/4" bolts, you are further limiting it.

The "assumption" isn't that it would be better then having it flush mounted. The assumption is that any flex would be insignificant. I don't perceive the Dan's Pier Plate with a concrete pier to have the same drawbacks as a 4 bolt pattered larger metal pier that I associate with ratcages.


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Midnight Dan
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Reged: 01/23/08

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Re: Pier diameter? new [Re: Footbag]
      #6051653 - 08/28/13 10:58 PM

I have to agree with Footbag. Take a look at the photos of my pier and 3/4" stainless anchor bolts farther up in this thread. They look less like bolts and more like large steel shafts that rival the counterweight shaft in size. With the 2-3 inches of length between the pier and the plate, they are not going to introduce anything measurable in terms of flex or vibration. Not happenin'.

From what I've seen of people referencing the "rat cage", it is not the bolts from pier to plate, but the area between two plates that are often connected with another set of bolts, frequently smaller than the anchor bolts. This is usually done to allow bolting through the bottom plate, and into the mount head from underneath the top plate, without the sets of bolts interfering with each other other the plates. It also works as something of an "adapter" in that the bottom plate fits the pier, while the top plate fits the mount head. If you build your own pier plate, this is a fairly easy way to do it. But if the plates or bolts are not heavy duty enough, they can introduce some flex or vibration.

I've eliminated the rat cage in my design by using flat aluminum plates between the top and bottom pier plates instead of bolts. "Dan's Pier Plates" eliminates the rat cage by using countersunk holes in thick plates, and short bolts to bolt the top and bottom plate right to each other.

-Dan


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StarmanDan
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Loc: Deep in the heart of Texas
Re: Pier diameter? new [Re: Raginar]
      #6059418 - 09/02/13 02:33 PM

Quote:

Dan, can you detail how you did the top of your brick pier?

Pictures?




So as to not hijack the thread I've updated my progress on my pier:

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5729183/page...


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