Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

How not to build a pier footer!

This topic has been archived. This means that you cannot reply to this topic.
330 replies to this topic

#26 Paula E

Paula E

    Non-standard Title

  • -----
  • topic starter
  • Posts: 2,247
  • Joined: 13 Sep 2007

Posted 12 February 2008 - 03:48 AM

I just don't think the problem is isolated yet.


It is kind of hard to believe. OK, I'll quit panicing and roll my sleeves back up and analyze this further...

Thanks Jerry. You're the second person who's suggested I investigate any electrical issues - so I'm definitely going to do that. I'm going to do some further testing before I do anything radical, that's for sure!

One thing I'll do is power the scope from a battery for a while and see if the seeing varies with other electrical loads on the AC circuit. (If it varies then it's not an electrical issue affecting the scope's tracking.)

I've got a paramount on order - it should be here soon, and I expect it will be a lot more stable. The larger Meades just can't be as stable - I'm sure you can build a fork that will hold a 12-14" scope that is rock solid, but I bet you can't build one that way that I can lift! Nothing against the meade either - like anything else it's a compromise design with inherent tradeoffs.

I thought about setting up the tripod, but I think it'll be better isolated because the feet on it are rubber. I may try that anyway.

Testing it outside the dome is a good idea too.

The most annoying part of all this is it's probably weekend after next before I can get out there again.

#27 rodney

rodney

    Vendor - Explora Dome

  • *****
  • Vendors
  • Posts: 1,489
  • Joined: 08 Mar 2005

Posted 12 February 2008 - 07:09 AM

Scott,
Question. Why was the outlet placed out that far from the pier?


'cause he did it wrong.

In your one image after the concrete pour showing the pier, what are those pads on the outside of the pier? That looks like the thick felt or whatever it is between my sidewalk pads.


Yeah, I think that's what it is. It was really all he was willing to do to isolate the pad. :(

I will definitely keep you posted as to how this all turns out!



Scott,
If the product is that felt stuff then simply remove it. Looking at the image the concrete guy did isolate the pier. Those pads should be removed. If the contractor did anything right he would have used that product all the way to the base. 6 inches or however deep the slab is. Get something long, thin and strong and ram it through that product downward. If it goes through there is your biggest issue.

Clear skies,

#28 Manny Myles

Manny Myles

    Hubble

  • *****
  • Posts: 18,888
  • Joined: 29 Nov 2005

Posted 12 February 2008 - 09:13 AM

You can cut the conduit, just yank the wires out prior to the surgery, you conduit will still be there, just cut, then fish the wires back through, they might get wet from
any ground water but they do have plastic covers on them but you can pull them through a larger plastic tube to protect them.
For the shop vac sucking the dust up, been ther done that, plan on frequent filters cleanings every few minutes. It does work but does a poor job as the rooster tail of dust comes out quite fast.
If I were to cut it, I'd wind up cutting at least a 1/2" slice out then removing this slice then if it were not cut through finish it off with a hammer and chisel, then filling the gap with sill sealer foam.
I'd try all avenues before cutting as this will be a mess.
The voice of experience from 30+ years in concrete consruction/destruction tells me so.
m2

#29 Telescopeman54

Telescopeman54

    Vendor - Trapezium Telescopes & Services, LLC.

  • *****
  • Posts: 1,715
  • Joined: 16 Aug 2007

Posted 12 February 2008 - 10:12 AM

I failed to notice that you had an adjustable pier. Sorry about that.

I like the idea of confirming that the slab is the culprit by moving the scope outside.

By the way, just how deep did you dig for your pier? You DID get well below the frost line, right? LOL

I'll be interested in hearing about the outside test.

CS

sbf

#30 kent

kent

    Viking 1

  • -----
  • Posts: 854
  • Joined: 16 Feb 2006

Posted 12 February 2008 - 11:17 AM

Good Luck Scott! My prayers go out to you. :praying:
One other thing you must have some wide set of sholders! :waytogo:

#31 Paula E

Paula E

    Non-standard Title

  • -----
  • topic starter
  • Posts: 2,247
  • Joined: 13 Sep 2007

Posted 12 February 2008 - 12:09 PM

By the way, just how deep did you dig for your pier? You DID get well below the frost line, right? LOL


The area under the pier is 3' deep - well below the frostline here. The winters aren't terribly cold here, so the frost line is quite shallow.

#32 Telescopeman54

Telescopeman54

    Vendor - Trapezium Telescopes & Services, LLC.

  • *****
  • Posts: 1,715
  • Joined: 16 Aug 2007

Posted 12 February 2008 - 12:13 PM

Three feet. Well, that shoots that idea down!

sbf

#33 Paula E

Paula E

    Non-standard Title

  • -----
  • topic starter
  • Posts: 2,247
  • Joined: 13 Sep 2007

Posted 12 February 2008 - 12:25 PM

If the product is that felt stuff then simply remove it. Looking at the image the concrete guy did isolate the pier. Those pads should be removed.


OK, I can certainly check that and remove them.

If the contractor did anything right he would have used that product all the way to the base. 6 inches or however deep the slab is. Get something long, thin and strong and ram it through that product downward. If it goes through there is your biggest issue.


I know the pads he used were quite small - they are MAYBE 6" deep - but the pier footer is a good 3 feet deep where he placed them. The pads definitely don't go all the way down. I guess if they did, my pier footer would only be a 1' x 1' x 3' - is that what you are thinking the problem is?

Anyway, I didn't know what that stuff was for, so I should remove it anyway?

#34 Bowmoreman

Bowmoreman

    Clear enough skies

  • *****
  • Posts: 9,664
  • Joined: 11 Sep 2006

Posted 12 February 2008 - 12:42 PM

Wow, that's fascinating Dave! I'd never heard of Sorbothane! OK, I see what you are saying.

I think what you suggest would get everything but the walls of the dome themselves. The dome weighs about 650 lbs, and the motors for it vibrate a good deal. Would it be possible to make shims of this stuff and put them between the sections of the walls where they are bolted together? (Otherwise I'd have to remove the shutter and dome, and install pucks of the stuff between a pair of the rings. Removing the dome is the labor intensive part of the process.

What about pads of sorbothane under the pier itself? The pier is mounted via j-bolts to a plate imbedded in the concrete. I can pretty easily remove it, and add material under it.


I was thinking more about this, and given the Pier Tech is a metal pier, I think you could do a couple of things (and it'd be relatively cheap to try):

1) Put sheet of Sorbothane between the Pier and the footing
2) stick some Sorbothane on either the inside (ideally, if possible) or the outside (less ideal, and maybe ugly) of the metal pier...

Either/both ways: it will reduce the higher frequency "ringing" quite a bit!

I'd recommend doing this on the CURRENT setup; it it works reasonably well for the Meade, it'll work even better for the Paramount.

And, if doesn't work, its not like you've invested HUNDREDS of $$ trying...

It *does* work for my record player, and my Pre-amp and D/A converter in my HiEnd Audio system though... Audibly reduces noise and harshness (the audible effects of vibrations)...

clear enough skies!

#35 Paula E

Paula E

    Non-standard Title

  • -----
  • topic starter
  • Posts: 2,247
  • Joined: 13 Sep 2007

Posted 12 February 2008 - 12:58 PM

Thanks Dave. Where might I find this stuff?

#36 Galaxyhunter

Galaxyhunter

    Mercury-Atlas

  • *****
  • Posts: 2,886
  • Joined: 02 Jan 2006

Posted 12 February 2008 - 01:06 PM

Scott,
When I built my OB, I poured everything in one shot. I had planned all along to cut the area around the pier. This worked just fine, I can walk around while imaging with out a problem.

#37 Pedestal

Pedestal

    Skylab

  • *****
  • Posts: 4,437
  • Joined: 11 Mar 2006

Posted 12 February 2008 - 01:14 PM

I think Jerry has some wise advice: do more testing before cutting. The sorbothane under the current pier might also be a simple fix. Try McMaster-Carr. link
Hubert

#38 JerryWise

JerryWise

    Cosmos

  • *****
  • Posts: 9,764
  • Joined: 26 Dec 2003

Posted 12 February 2008 - 07:27 PM

I tried sorbothane on my pier when I was using a CGE mount and also with an RCX 10" fork on the same pier. The sorbothane comes in sheets and is effective with proper thickness. However, you have to tighten the starch out of mount bolts which pull the sorbothane into a thin ineffective sheet. Also, loading and vibrations transmits through the bolts as well as the base so there was no gain (for me anyway). Any absorbing material needs an area of motion or expansion and contraction in which to work. Like the sping/shock absorber combination on vehicles. Compression between pier and mount or pier and base eliminate working area of these materials. You want rock solid from the pier to the scope on the mount and I'm betting Scott already has a very solid pier. That Paramount will likely solve all his vibration problems.

#39 Bowmoreman

Bowmoreman

    Clear enough skies

  • *****
  • Posts: 9,664
  • Joined: 11 Sep 2006

Posted 12 February 2008 - 09:30 PM

Wow... don't... remember... my last, acquisition, was, ahem, probably 15 years ago...

the stuff DOES work... but...
you have o use enough (thickness)...

I'm guessing that for pier usage, you'd need double or triple thickness under the pier, and between the pier and the mount...

But it's real value is reducing "ringing"... for that surface mounting is, ahem, "paramount"...

but... ugly...

on the other hand it is cheap...

I haven't tried, but maybe google "sorbothane", alternatively, high-end music sources might have links/pointers (Acoustic Sounds, Music Direct are two mail order places that come to mind).

clear enough skies

#40 JerryWise

JerryWise

    Cosmos

  • *****
  • Posts: 9,764
  • Joined: 26 Dec 2003

Posted 12 February 2008 - 11:55 PM

I was thinking through my post above on sorbothane and don't think I explained it correctly. Let's say we want to sorbothane or cushion a pier and mount by putting 1/4 inch of it between the pier and the footer. Then, for effect since you have to isolate the bolts too, you add 1/4 inch under the bolt washers between the washers and the pier base. The pier is now sitting on 1/4" of flexible (sorbothane has the consistency of a rubber compound) vibration absorbing material. To absorb, it must compress and relax. The vibration is going to induce a motion which will then result in a countermotion which is dampened by the 1/4" sorbothane. Your pier is now sitting on 1/4" of flexible material. Consider the pier, mount and scope will extend 5 feet or so above the 1/4" of rubber like material. A lot of moment arm on compressible material. I even tried it on the base of the mount atop the pier and had the same problem.

So you then carefully counterbalance the scope and slightly weight bias the counterweights toward the counterweight side as most do(keeps the gears loaded for better tracking). This means the mount/scope/pier combination is not perfectly balanced. So you begin viewing or photography in the east. The pier will be slightly tilted to the east as the counterweights are on that side. Change to a target in the west and the pier will be tilted slightly in the other direction as the weights are then over on that side. Now, imagine what this does to polar alignment. Others with more expertise may give the correct way to do this if I'm in error. I spent several months with sorbothane, rubber mats, shock devices etc. From what I've seen, sorbothane works best under speakers on coffee tables. Solid attachment on solid equipment is needed for jiggle free images and visuals.

Carl (GalaxHunter) and I both have the same cemented in pier arrangement and both are reporting no problems under test conditions and imaging (me) conditions. Maybe someone that has the same cemented in pier arrangement as we do that has had a problem could chime in. Also, someone that has actually used sorbothane on a mount that has a technique of tightening the pier bolts or mount bolts without compressing out the dampening action and still hold the scope steady and in polar alignment could chime in. I'm very concerned Scott is close to spending a lot of money and effort for a "snipe hunt". (Goggle if not familiar)


#41 Bowmoreman

Bowmoreman

    Clear enough skies

  • *****
  • Posts: 9,664
  • Joined: 11 Sep 2006

Posted 13 February 2008 - 05:34 AM

Jerry, you make excellent points. the bolts will (and have to be) a solid conduit by passing the sorbothane... if you didn't things would wobble...

I also wasn't clear enough in my early AM rambles... my idea was that the sorbothane - in contact with pier and/or mount, might reduce the higher frequency vibrations that WERE there, not that it would insulate them from getting there in the first place...

it would obviously do NOTHING for gross movements (lower frequency vibrations from footfalls, etc.)... But, based on my experience in audio, it *probably* would do something to reduce the amplitude of the higher frequency vibrations Scott noticed from those fans... You'd be amazed what 60 Hz hum can do in terms of creating vibrations! And, those fans are almost certainly operating at, or above 60 Hz/cycles/revolutions... And Sorbothane works fabulously at filtering out the vibrations caused by power supply transformer hum... (at least for me and many other audiophiles)...

A single sheet of the stuff *should* still be relatively cheap (from memory last time I bought it it was around $20 or so)... and would be quick to see IF it had any salutory effect...

But, again, on reflection, putting it between mount and pier, and/or pier and footer, probably would, as you point out and for your reasons, be a waste...

Clear enough skies

#42 JerryWise

JerryWise

    Cosmos

  • *****
  • Posts: 9,764
  • Joined: 26 Dec 2003

Posted 13 February 2008 - 08:13 AM

Dave, it is also the filler for vibration surpression pads and does a fabulous job for it's intended purpose. As mentioned earlier, the problem needs a little further identification before cutting concrete or remounting the pier on various materials.

Sorbothane can be obtained at a very good price here at Edmund Scientific. I also have several pounds of very compressed Sorbothane sheets that won't absorb any Hertz hum....... cheap. (It was used between the mount and pier for one night.) The material under heavy prolonged stress will tend to fail (go flat) as described here under viscoelastic creep. I also tried sorbothane under the telescope where the OTA attaches to the mounting plate. On very cold nights it turns to stone (see effect of temperature at the site referenced).

I'm certainly not an expert on visco-elastic polymers and can only speak from limited experience putting it on the pier and mount. (It does work great under the observatory radio.) Is there another place on the mount other than in the high weight areas it could be placed to reduce the 60hz hum mentioned?

#43 Paula E

Paula E

    Non-standard Title

  • -----
  • topic starter
  • Posts: 2,247
  • Joined: 13 Sep 2007

Posted 13 February 2008 - 11:27 AM

Thanks for the advice Dave & Jerry. I'll likely get some of the sorbothane anyway, for use under things like my PC. It sounds like it will be a useful tool, if not a silver bullet.

Next time I'm out there, I'm setting up the Meade DSI that I bought for cheap on a whim, and I'll work on characterizing the vibration better.

#44 mikey cee

mikey cee

    Cosmos

  • *****
  • Posts: 9,589
  • Joined: 18 Jan 2007

Posted 13 February 2008 - 01:49 PM

Scott...Hope this all plays out OK. I know that to the average contractor this is "much ado about nothin'". But having been in the consruction business there is an extremely high number of absolute SLUGS that try to pass themselves off as craftsmen or true artisans of their trade. Advice to others...don't just shop price, get references and check out their workmanship! As a general rule of thumb if their jobs look neat, flat, true and square the job is probably most likely done to specs and code. :smirk: :whistle:Mike

#45 dgs©

dgs©

    Hubble

  • *****
  • Posts: 15,137
  • Joined: 29 Mar 2004

Posted 13 February 2008 - 05:26 PM

The mount needs to be cinched down snugly with bolts, so the sorbothane won't do much good there.
On the other hand, the things that are doing the excitation could do with a few layers underneath to keep their vibes from getting into the foundation to begin with. ;)

Doesn't do much for walking around on the floor, but you could probably sit quietly in a chair while collecting images or stand still at the guide scope. Maybe the antifatique matts I mentioned before would dampen the effects of walking around. :shrug:

#46 Spaz

Spaz

    Viking 1

  • -----
  • Posts: 758
  • Joined: 19 Jan 2007

Posted 13 February 2008 - 07:34 PM

Scott, unless it's really impractical (too expensive, dangerous, dirty, difficult, whatever), seperating the pier and slab is a good idea anyway, even if it doesn't cure all your other vibration issues.

I recommend biting the bullet and making the cuts, unless it's a job that belongs in the 'too hard basket', in your particular case.

#47 Telescopeman54

Telescopeman54

    Vendor - Trapezium Telescopes & Services, LLC.

  • *****
  • Posts: 1,715
  • Joined: 16 Aug 2007

Posted 13 February 2008 - 11:53 PM

I agree with Mikey Cee that to slump contractors this is a pain and they think they know more than you. I have done a lot of custom work for people in the past. Many times it was necessary to completely redo the work from scratch because the customer went with the lowest bidder. Learn from the never ending issues with the M-16 and you'll KNOW what I mean!! LOL

By the way, I'm very proud to say that I never needed to advertise. ALL of my work was ONLY from references. The work, all in NYC, ranged from security and entry systems to interior reconstruction/remodeling to steel reinforcing of old brownstone foundations. Many times the people were told it was impossible or the cost was extremely high. I always found an answer and many times it was for less money because I charged for actual man hours worked instead of a project price.

There has been some very good advice and some solid ideas presented here. I'm still going to hold to the belief that you will need to cut the concrete pad back about an inch away from the pier to solve your problem. If I'm wrong, so be it. However, that would be my expectaion.

Good luck on the testing and I will look forwad to knowing the results.

sbf

#48 Paula E

Paula E

    Non-standard Title

  • -----
  • topic starter
  • Posts: 2,247
  • Joined: 13 Sep 2007

Posted 14 February 2008 - 11:51 AM

Scott...Hope this all plays out OK. I know that to the average contractor this is "much ado about nothin'". But having been in the consruction business there is an extremely high number of absolute SLUGS that try to pass themselves off as craftsmen or true artisans of their trade. Advice to others...don't just shop price, get references and check out their workmanship! As a general rule of thumb if their jobs look neat, flat, true and square the job is probably most likely done to specs and code. :smirk: :whistle:Mike


I agree with Mikey Cee that to slump contractors this is a pain and they think they know more than you. I have done a lot of custom work for people in the past. Many times it was necessary to completely redo the work from scratch because the customer went with the lowest bidder.


Well, in my case it wasn't so much the lowest bidder as getting anyone to take the job - period. Finding people to do good work out here is difficult.

I'll keep y'all posted. I have a variety of things to test and try now. I will likely hold off on cutting the concrete, at least until I can characterize this better. I won't be able to do anything this weekend - so it won't until be the following one that I really have any sort of update.

I believe I'm going to approach it like this:
1. Setup the Meade DSI camera I have and repro the vibration issue I see - possibly capturing the video.

2. Double check my present telescope and mount and its attachment to the pier.

3. Double check the pier's attachment to its plate. Maybe stuff is just loose.

4. Try to verify if the issue with the little heater is mechanical vibration, thermal, or electrical in nature.

5. Put the meade scope on its tripod in the dome, and see if the problems persists. (I guess I could also try to set the scope base on the ground and see how that affects things.)

6. I'll possibly have the paramount / planewave before I get much chance to diagnose this further, so if I do I'm liable to try them. The issue may be very different, or not present at all with the more stable mount.


I'll cut the slab if I have to - but I really do hope that's a last-resort type of situation.

I do appreciate all of the suggestions!

#49 Manny Myles

Manny Myles

    Hubble

  • *****
  • Posts: 18,888
  • Joined: 29 Nov 2005

Posted 14 February 2008 - 12:25 PM

If you do have to cut, do yourself a favor and rent a 14" diamond blade as the common abrasive blades wear down fast and then don't give you depth of cut you want.
m2

#50 mikey cee

mikey cee

    Cosmos

  • *****
  • Posts: 9,589
  • Joined: 18 Jan 2007

Posted 14 February 2008 - 04:37 PM

Scott....Manny is right rent a 14" diamond blade saw. Allowing for the arbor washer it should get you down 6"+ enough to reach dirt. Don't be too concerned about neatness here. Once the cuts are completed make sure you allow for the rounded nature of the blade by cutting beyond your corners. Then simply fill your cuts with liquid self leveling Vulkem sealant in the quart size tubes. You got to bite the bullet here and get on it.....unfortunately no real shortcut to a solution exists here. :smirk: ;)Mike


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics