Keith Howlett
professor emeritus
Reged: 03/06/07
Posts: 710
Loc: Northumberland, UK
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Hi All,
It's a bit of a long-shot, but does anyone know if fiberglass skinned domes with wooden ribs have any expansion or stress cracking issues?
I'm considering reinforcing my fiberglass dome with some internal wooden ribs with a view to widening the slit opening.
Thanks,
Keith
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14" f10 RCOS / AP1200
AP 105 Traveler / AP400 QMD
Coronado SM90 Filter
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1965healey
Carpal Tunnel
Reged: 06/23/07
Posts: 2844
Loc: San Antonio, TX
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Wood, if exposed to extremes of temperature and humidity, can swell, shrink and warp due to how those extremes effect the moisture content of the wood. Older, drier, more dense species of wood will be less affected by them. Engineered wood that is laminated is less affected as well. Ribs made of high quality plywood that has glues rated for areas that may be exposed to damp should hold up fairly well. Encapsulating the ribs in fiberglass cloth and resin should pretty much eliminate the effects of moisture and any resulting shrink or swell moisture may cause. Wood is certainly a much cheaper and more forgiving medium to work in than steel or aluminum. Care must be taken to insure that any penetrations to afix the new ribs to the exisiting dome are well sealed to prevent leaks. 
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1965Healey (Karen)
Woodlawn Lake Observatory
Celestron CPC 800/FT MIcro/APT Wedge
SV NHNG 80mm #0261/CG5-GT
Celestron Omni 150 XLT
Losmandy rails/rings
Starizona CWeight system
Celestron Neximage
Sony a100 DSLR/ZigView S2
Meade DS60's w/Autostar (2)
Meade LPI/Meade DSI-C/DSI ProII
750cc Honda Shadow Spirit (Thanks Dad!)
1965 Austin Healey 3000 MKIII
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Keith Howlett
professor emeritus
Reged: 03/06/07
Posts: 710
Loc: Northumberland, UK
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Hi Karen,
Thanks for the tip!
The dome is an attractive rib-free structure at present - so it will free-stand, but perhaps not so well if I take a big cut out around the slit.
I'm considering placing a wood horse-shoe around the shutter slot of I enlarge it, and then running perhaps six curved ribs down to the dome rim for extra support. I have seen several quite spectacular domes made from wood on CN in the past.
I've generally got around the water ingress through holes problem using a stainless bolt and washer that pulls down onto neoprene washers contacting the inside and outside of the fiberglass. If you snug them up every year or two that seems to work well.
Thanks,
Keith
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14" f10 RCOS / AP1200
AP 105 Traveler / AP400 QMD
Coronado SM90 Filter
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kiwisailor
Pooh-Bah
Reged: 01/07/04
Posts: 1110
Loc: Lyttelton, New Zealand
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G'day Keith
Look at the "West Epoxy" system for this project, down in this neck of the woods, we spend a lot of time building boats in GRP, timber and composites of both. Your dome will be Polyester GRP based, with suitable preparation, epoxy will bond to that. Have a look at boat repair books/web pages, or have talk to your nearest boat builder.
This montage is of a boat a mate and I brought damaged, and repaired- if this can be done and keep the ocean out, your project should be easy peasey 
Steve
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Don't wait until tomorrow, start procrastinating today!
Sky-Watcher 8" F5 Newt
Mmmm Moonlite CR2
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Keith Howlett
professor emeritus
Reged: 03/06/07
Posts: 710
Loc: Northumberland, UK
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Wow!
Fantastic result with the boat - I am inspired!
Thanks,
Keith
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14" f10 RCOS / AP1200
AP 105 Traveler / AP400 QMD
Coronado SM90 Filter
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Tom Clark
super member
Reged: 11/14/07
Posts: 144
Loc: Chiefland, Florida
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Quote:
Hi All,
It's a bit of a long-shot, but does anyone know if fiberglass skinned domes with wooden ribs have any expansion or stress cracking issues?
I'm considering reinforcing my fiberglass dome with some internal wooden ribs with a view to widening the slit opening.
Thanks,
Keith
Keith, Your question reminded me of this photo taken while my dome was under construction. This may give you a few ideas. My dome had 33 ribs, then sheeted with 1/4" plywood, then fiberglassed. It is still like new and was built in 2002. You could either screw the ribs in or glue them in with fiberglass, depending on the size of your dome.
My dome construction is shown here:
http://tinyurl.com/2ozsvc
Tom
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Keith Howlett
professor emeritus
Reged: 03/06/07
Posts: 710
Loc: Northumberland, UK
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Hi Tom,
That is extremely useful. Essentially I am looking at putting in a wood dome frame and skinning it with the existing fiberglass dome and walls. This will allow me to make two useful changes. I can enlarge the slit and replace the dome rotation system. Luckily I have a great (and reasonably priced) local carpenter who will make a much better job of it than me.
I have two quick questions...
1) Have you found the rolled angle steel ring and plywood to be stiff enough to support the dome without sagging?
2) Did you consider doing the rotation track and wheels the other way up (i.e. track on the wall and wheels on the dome ribs) to minimize the moving mass?
I'll post this as a separate thread, but the part that is causing the most head scratching is designing a replacement shutter system for the wide slit.
Many thanks,
Keith
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14" f10 RCOS / AP1200
AP 105 Traveler / AP400 QMD
Coronado SM90 Filter
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Chris Schroeder
Postmaster
Reged: 12/11/04
Posts: 5098
Loc: N.E. WI Sky Glow
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Nice rehab of the boat
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Chris
Mallincam Color Hyper Plus
10" DSH with SC DSC, CPC 800 XLT
M102ED S.V., ZS 80FD 10th Anniv, ZS 66SD, PST
POD XL3 http://POD.SchroederCity.com
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Tom Clark
super member
Reged: 11/14/07
Posts: 144
Loc: Chiefland, Florida
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1) Have you found the rolled angle steel ring and plywood to be stiff enough to support the dome without sagging?
The angle iron is quite stiff and the dome rotates easily on it.
2) Did you consider doing the rotation track and wheels the other way up (i.e. track on the wall and wheels on the dome ribs) to minimize the moving mass?
Keith, I just guessed that the dome would would not be as stiff as the walls, so the angle iron is under the dome to help make it stiffer. I never considered doing it the other way.
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Keith Howlett
professor emeritus
Reged: 03/06/07
Posts: 710
Loc: Northumberland, UK
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Ah, I understand. A much larger dome like yours would pose a much bigger stiffening problem than mine.
My other thought was that I would find it easier to level a track on the wall than on the dome. I like being in the dome and if I can keep the rotating mass down I wouldn't have any pressing need to motorize it either.
Cheers,
Keith
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14" f10 RCOS / AP1200
AP 105 Traveler / AP400 QMD
Coronado SM90 Filter
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kiwisailor
Pooh-Bah
Reged: 01/07/04
Posts: 1110
Loc: Lyttelton, New Zealand
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G'day Keith
Instead of wooden ribs, you could look at "glueing" foam ribs and then building up some layers of glass cloth over them, fair them up with a bog made from resin and micro ballons and then gel coat the inside of the dome.
Here's a shot of showing what I mean.
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Don't wait until tomorrow, start procrastinating today!
Sky-Watcher 8" F5 Newt
Mmmm Moonlite CR2
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 12070
Loc: Rockford Illinois
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Nice thought... No weight added from the "Ribs", and all is does is hold a "Form" for the glass which becomes the strength... 
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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kiwisailor
Pooh-Bah
Reged: 01/07/04
Posts: 1110
Loc: Lyttelton, New Zealand
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Quote:
No weight added from the "Ribs", and all is does is hold a "Form" for the glass which becomes the strength.
Got it in one Jeff 
Steve
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Don't wait until tomorrow, start procrastinating today!
Sky-Watcher 8" F5 Newt
Mmmm Moonlite CR2
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Keith Howlett
professor emeritus
Reged: 03/06/07
Posts: 710
Loc: Northumberland, UK
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Okay - I got it in two! It's just like adding a box section rib. That's clever.
Cheers,
Keith
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14" f10 RCOS / AP1200
AP 105 Traveler / AP400 QMD
Coronado SM90 Filter
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