Photon
sage
Reged: 03/10/06
Posts: 278
Loc: Aurora, Colorado, USA
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When I taught middle-school science, I used to make a "seismograph" in the classroom that would pick up vibrations from traffic a couple of hundred feet from my room.
I guess pier construction has been well thought out, and yes, I'm a newbie, but....
I'm wondering if having such a rigid pier material as concrete or steel might not just transmit vibrations better than something more flexible like wood. Any thoughts?
Pete
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Zack DeMoss
sage
Reged: 03/08/06
Posts: 252
Loc: Roanoke, VA
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Interesting thought. I think though that you would need something more durable than wood, but i do know they use essentially "Rubber boots" in plants that manufacture microchips to avoid vibration.
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10X50 Brusnell Bino's
8" Dob
4.5" Meade Reflector, Homebuilt Mount.
Zack DeMoss
Old Dominion University
Information Technology Major
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imjeffp
Aluminum Falcon
Reged: 09/30/03
Posts: 6103
Loc: Cedar Park, Texas
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How about using a railroad tie?
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 14043
Loc: Rockford Illinois
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Wood would (Try that 10 times real fast!) also vibrate. Think about it. Trees sway in the wind. If it didn't have some "Give" to it, it would break.
I think what stops (Or at least slows down/dampens) vibrations through a concrete pier is a combination of Mass, Large Footing, Diameter of Pier, Internal Reinforcement... All that works in sync to help limit vibrations.
If I recall correctly, the rule of thumb for a concrete pier is at LEAST the same diameter of the scope you'll put on it. Going 2" larger is my plan. (10" LX200, 12" pier).
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Neo... (Jeff)
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10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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John Jarosz
Astro Gearhead
Reged: 04/25/04
Posts: 3026
Loc: Chicago area, IL
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All materials are compromises.
Wood transmits vibrations worse than steel or aluminum. I am not sure about concrete.
However, wood is more elastic than any of the other common construction materials. So to build a wood pier that is the equivalent stiffness of a steel or concrete pier, a much larger cross section is required. At some point the cross section of the pier will get too large to get close to the scope for observing, so it may not be possible to build a pier with the same stiffness as steel or concrete in the space available.
So a design that commands a certain material be used may impose constraints that will still allow you to solve the problem, but not make something that can be used efficiently.
The difference in vibration damping between wood and concrete may not be enough that entices people to spend time trying to use wood for a pier. Concrete is a pretty dead material, and it is much stiffer than wood which permits a more compact design..
A design effort using either material may well prove sucessful, but to optimize a solution the analysis needs to be done numerically.
Once you start numerical analysis, you need answers to all sorts of questions:
Frequency, magnitude and direction of expected vibrations that are required to be damped?
Time permitted to reduce same vibrations?
Magnitude, etc of acceptable levels of vibrations after damping?
At this point most people start to think about seat-of-the-pants judgements instead of measuring everything. So the question never really gets answered empirically, but rather on a case-by-case basis, where everything is analyzed after the fact, but again not using instrumentation that gives measurements, but by observational subjective data.
Will wood work? Yes. Is it better? That depends...........
John
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6" F4.6(w/Paracorr) Reflector , 8" F11 Dall Relay Scope ,
6" F5 RFT Refractor w/Istar Obj , G11 Mount Gemini1 Level 4
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RoundStars
scholastic sledgehammer
Reged: 07/09/08
Posts: 794
Loc: Northern NH - Bortle 2-3
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I recall from college physics classes that steel is highly elastic, meaning that it will return to its original position when flexed. This is vibration. It's well known that steel piers vibrate. It's also well documented that concrete will readily transmit vibrations, and that tripods shouldn't be erected on concrete pads. It's also well documented that telescope tripods are built of wood because they dampen vibrations. Wood is not a highly elastic material. Rap a wooden fence post and it goes, "Thunk": no vibration at all! I think a wooden pier is a terriffic idea,and I intend to pursue the concept full-tilt.
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GJJim
scholastic sledgehammer
Reged: 09/09/06
Posts: 907
Loc: Western CO
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Wood "moves" (changes dimensions) as its moisture content changes due to local conditions. If you build a wood pier and get everything aligned, six months later the alignment will change. If that won't bother you, then go ahead and use wood. It is inexpensive, relatively easy to work, and definitely more attractive than steel or concrete.
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LarryinCA
sage
Reged: 09/26/03
Posts: 470
Loc: Sonora, CA
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My pier is four pressure treated 4x4's bolted together in two directions at three places along it's length and sunk in 18" of concrete. May not be adequate for AP, but works great for my visual observing. Yes, if I bump the mounting plates there is some vibration but it dampens quickly.
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Larry KQ6PJ
Phoenix Lake Dorkatorium
CPC 1100XLT
Orion XT10 Intelliscope
AT66
WO Binoviewer
Oberwerk 11x56
Orion Mini Giant 8x56
SkyShed POD XL3
More eyepieces than I need
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johnfdean
Pooh-Bah
Reged: 06/04/06
Posts: 1104
Loc: southern tip of Illinois
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Interesting idea. I think the biggest problem is the moisture issue affecting allignment. But that could be mitigated somewhat by sealing. I suspect I will sink a 6x6 in the ground somewhere on my property and use it for my 4" to test out the idea. It won't be too difficult to remove if it doesn't work out.
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Celestron C6 f/5 by Vixen with Polaris GEM
14" Tscope dob f/4.7 with Argo Navis
80mm Nighthawk on Eq 2
Celestron C-4 f/10
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Achernar
Postmaster
Reged: 02/25/06
Posts: 7805
Loc: Mobile, Alabama, USA
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Steel and aluminum does transmit vibration but some people have filled the pier with sand to deaden vibrations. In observatories regardless of what the pier is made of, it's isolated from the floor and the rest of the building on it's own foundation. If you pour a concreted floor for your observatory, it's a good idea to mount the pier on a separate pad from the rest of the floor to isolate any vibrations caused by you moving around on the floor. Some kinds of wood could be used to make a pier, but I would heavily seal it to minimize expanding and contracting in response to temperature and humidity changes. Wood can warp as well, a fact I constantly do battle with here while woodworking. A high quality plywood would likely work far better than solid lumber, and it's much less apt to warp. Airplanes have been built mostly out of plywood, so it certainly can be used to build a pier.
Taras
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15-inch F/4.5 Homebuilt truss-tube Dob with Sky Commander digital setting circles.
10-inch F/4.5 Discovery Dob with JMI digital setting circles.
6-inch F/8 Homebuilt Dob
24, 18, 14, 11, 8.8, 6.7, 4.7mm ES 82 degree eyepieces.
21, 13, 8, 5 and 3.5mm Orion Stratus eyepieces.
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BlueMoon
sage
Reged: 06/14/07
Posts: 388
Loc: Idaho, USA
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Quote:
A high quality plywood would likely work far better than solid lumber, and it's much less apt to warp. Airplanes have been built mostly out of plywood, so it certainly can be used to build a pier.
Got me thinking. I have to go 12' in height to clear some obstructions in my backyard and I've been pondering what to use for the pier. I've been considering 8-10" pipe until now.
Your post reminded me of building some ship masts from individual lengths of plywood, scarfed together for length and then wrapped with a single layer of fibreglass for protection from the weather. The mast sections were hexagonal and fairly simple to build with a simple "birds mouth" router jig and a table saw.
They were very stiff and I don't recall much vibration being transmitted to the hull even though we had some taut back and forestays that were prone to vibrating when the wind kicked up...
Might have to ponder this a bit more...
Cheers.
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Jeff
Herrett Observatory, Twin Falls, Idaho.
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divers
professor emeritus
Reged: 01/21/08
Posts: 577
Loc: Apopka, FL
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Jeff -
A very interesting idea. Wonder if I could take 4 4x4's, screw them together, wrap in glass mat and fiberglass the whole thing. Sink the now sealed pole 5-6 foot down and have a nice stable platform for visual and photography. Since I have the 4x4's already...I might try this...anyone see anything stupid about this?
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Black tube C11
Siebert 7mmUltra and 13mmUltra
Siebert 2x 2" Barlow
GIRO II on a Meade tripod
12" Starhopper
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atnbirdie
super member
Reged: 12/10/06
Posts: 179
Loc: Middletown, MD
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Like Larry, I have a wooden pier constructed of 4 bundled 4x4s. I have mine bolted together from all 4 sides with lag bolts in several locations along the length plus I added construction grade glue to bond them together. My pressure treated pier is buried about 40" deep in cement in clay soil and only extends about 50" above the ground.
I hadn't thought of the changes due to changing water content. However, I'm not concerned about that as I am a visual observer. Should my alignment start seeming a bit off, I'll just redo it as needed.
I find the pier seems rock solid. I can jump up and down in my observatory and the scope doesn't vibrate a bit. I am located in a cul-de-sac so don't have anything but slow moving vehicles maneuvering closer than about 40-50 feet of the pier.
One advantage to wood is the ability to easily hang my power supply and a couple of other items from the pier itself with wood screws.
Finally, I made my mounting plate out of wood too. I used 3/4" plywood sandwiched with 1/8" hardboard. An upper disc is the size of the CPC base, the lower disc is about 13" in diameter and has holes cut around the perimeter for 1.25" and 2" eyepieces. The lower disk is screwed into the top of the pier with lag bolts. The two disks are connected with 3 threaded 1/2" bolts that I use to adjust height and level the scope.
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Steve
Orionis Observatory (ExploraDome)
CPC1100 XLT; NexStar 8SE; Stellarvue SV102ED; Orion ST-80; Lunt LS60THaPT
-Denkmeier S-1 Shorty Power/Filter Switch
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rodney
Vendor - Explora Dome
Reged: 03/08/05
Posts: 1306
Loc: Asbury, NJ
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Wood and fiberglass are a bad combination. Primarily it will trap any and all moisture inside the encapsulated wood, thus rotting it out prematurely. This was a huge problem for years in the boating industry. So much that most manufacturers no longer use any wood products in the production of their boat hulls. I am in the process of rebuilding my steel pier and went through the process of dealing with the wood pier option. I realized that even though wood is low cost that steel is the premium option when it comes to a telescope pier. However, there is always a however, if AP is not an option then wood can work for the individual. Fiberglassing is not really needed, however a good layer of paint will make the wood look good and protect the user from splinters and such.
Clear skies,
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Explora Dome information can be found here:
www.exploradome.us
Rodney
13 Truss
Canon XSi
Extremely happy Explora Dome home observatory owner
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BlueMoon
sage
Reged: 06/14/07
Posts: 388
Loc: Idaho, USA
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Quote:
Wood and fiberglass are a bad combination. Primarily it will trap any and all moisture inside the encapsulated wood, thus rotting it out prematurely. This was a huge problem for years in the boating industry. So much that most manufacturers no longer use any wood products in the production of their boat hulls.
I must respectfully disagree with this. I build wood strip canoes and small craft from both marine grade plywood and good old air-dried oak, sitka spruce and other woods. All my hulls have been covered with a single layer of 'glass to provide abrasion resistance and protection from the elements. I've yet, in the 30+ years of building these craft, had one hull rot due to moisture in the wood.
That being said, I have seen numerous wood and 'glass craft that have rotted out under the 'glass, but the cause could be traced to either a high moisture content in the wood (it wasn't dried properly), bad lay-up of the 'glass (created voids) or bad design of the hull (moisture trapped in places where it shouldn't be).
Two reasons why wood craft declined in production were due to the rising cost of good quality wood and the cheaper production of FRP hulls. But you can still find shops, mostly in the historical boat building areas of the US North East producing traditional wooden hulls.
My point is this: if the wood is properly dried and has a moisture content within acceptable limits for the humidity and temperature range it's expected to be used in, there is no reason why it can't be used, with or without 'glass. As a matter of fact, a good 'glass covering will help maintain the moisture content of the wood, further stabilizing it dimensionally.
Four 4x4 pieces of good wood, of lumber yard grade, clear grained if possible and with few knots, properly dried, through bolted and covered with a single layer of 'glass should last years. If properly matched when bolted, any cupping or warping of the pieces can generally be corrected.
If one wishes to be extra sure to guard against rot, pressure treated lumber could be used. However, more care must be used to see that the 'glass bonds to the surface properly. Personally, I would use untreated wood.
It should be possible to either bury the post in the ground using traditional concrete and pad methods. Just make sure the 'glass is well wrapped and sealed. Or, I would pour a pad slightly above grade and use angle iron through bolted to the post and bolted to the pad to provide support. A little silastic sealant in the bolt holes will ensure no moisture can penetrate at those points.
BTW, I apologize if I sound a little pedantic and no offense intended by dint of my opinion...
Cheers.
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Jeff
Herrett Observatory, Twin Falls, Idaho.
Edited by BlueMoon (03/09/09 02:08 PM)
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Jeff J
super member
Reged: 12/17/05
Posts: 187
Loc: Austin, Tx
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I am finding this thread very interesting. There have been numerous threads on concrete and chimney-block piers. And I've read through some of them so hear the horror stories. (One guy did a 2nd story pier and had to chip out most of the concrete out of the rebar because of air pockets and adhesion issues - then build a form and pour by hand).
The boss told me I could build a roll-off observatory on our house. It would be on the second story. So a wooden column getting up to that point would sure be easier to build than a concrete column. First she told me to get caught up on other chores....so this is still in the planning stages.
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There are many intelligent species in the universe. They are all owned by cats.
Jeff J.
Meade 10" LX200GPS + 2" W.O. dielectric diagonal
9mm, 12mm, 17mm Naglers; 24mm Pan, 8-24mm TV zoom
Austin, TX
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LarryinCA
sage
Reged: 09/26/03
Posts: 470
Loc: Sonora, CA
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Quote:
Like Larry, I have a wooden pier constructed of 4 bundled 4x4s. I have mine bolted together from all 4 sides with lag bolts in several locations along the length plus I added construction grade glue to bond them together.
Exactly what I have and it is working great.
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Larry KQ6PJ
Phoenix Lake Dorkatorium
CPC 1100XLT
Orion XT10 Intelliscope
AT66
WO Binoviewer
Oberwerk 11x56
Orion Mini Giant 8x56
SkyShed POD XL3
More eyepieces than I need
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divers
professor emeritus
Reged: 01/21/08
Posts: 577
Loc: Apopka, FL
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Any of you guys with the 4 4x4's willing to send me some pics or point me to the proper thread. I think this is the way I will go. Just need to plan.
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Black tube C11
Siebert 7mmUltra and 13mmUltra
Siebert 2x 2" Barlow
GIRO II on a Meade tripod
12" Starhopper
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LarryinCA
sage
Reged: 09/26/03
Posts: 470
Loc: Sonora, CA
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divers,
Give me a couple days and I will PM you some pics.
I got the idea and assistance from a Yahoo wooden pier forum which no longer seems to exist.
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Larry KQ6PJ
Phoenix Lake Dorkatorium
CPC 1100XLT
Orion XT10 Intelliscope
AT66
WO Binoviewer
Oberwerk 11x56
Orion Mini Giant 8x56
SkyShed POD XL3
More eyepieces than I need
Edited by LarryinCA (03/09/09 08:55 PM)
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Timber
professor emeritus
Reged: 11/08/08
Posts: 509
Loc: SW foothills of Mt. St. Helens
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Hi Larry,
How about posting the pics here on this thread so we all can see them.
Richard
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My four beautiful Saluki's; Barron, Sophie, Majnun and Kassandra, Now includes two Min Poodle lap dogs, Lady and Clues and I live on a small, rural, remote farm.
No close neighbors,
No streetlights,
No private security lights,
No power poles,
No traffic,
No TV,
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No Mosquitoes
Rather Wonderful
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