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Advice Needed - Wood for Roll off Observatory

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#1 kpendlebury

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Posted 23 November 2012 - 12:51 PM

Hi folks,

I intend on build a roll off observatory. It will be a fairly small thing at ~6x8. I live in Texas and the summers are bordering on brutal. In addition to this, a single day here can show temperature variation of sometimes up to 30 degrees (not always, but it happens).

While fairly handy, I don't have a great deal of construction experience, especially for outdoor projects. I am concerned about the type(s) of wood selected and I am unsure about warping. There are certain parts of the observatory that can warp a bit without much worry, but there are also certain parts that need to remain as straight as the day the were installed (like the roof track supports). Pressure treated pine is very popular here in Texas... it's abundant and cheap. That said, I can't really find a lot of information about its suitability for projects like this.

Has anyone done this with all pine before? Skyshed plans call for spruce for certain parts (like track supports), but that wood is not really available here in the south.

Any advice?

Thanks for your help.

#2 Lorence

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Posted 23 November 2012 - 02:56 PM

You use the same kind of wood that is used in house construction. Take a look at the big piles in your local lumberyards. They're not there for building birdhouses. All wood will warp to some degree. You just have to live with it.

I assume you are concerned about the rails. If it is going to keep you up at night then make your beams out of laminated plywood.

There are a few important things you should be worried about at this point. Heat, dust, unwanted guests etc. These could cause problems that will plague you for the life of your observatory. If one of your rails warps 1/4 of an inch you won't ever notice it. Set you mind to worrying about something worth worrying about.

A 30 deg change in temperature can happen anywhere in the central plains. You won't be the first one to have to deal with those conditions. I did very successfully. As for warping and shifting, I dealt with that as well.

Take a look at the archives of this forum and a few others. See what sort of problems people have with their observatories. That's how I started. Then I designed my building to avoid those problems. Much of what I did and why I did it is documented in my website.

#3 roscoe

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Posted 23 November 2012 - 03:28 PM

Ken,
The biggest problem with PT lumber is that t is normally pretty wet - it has a high internal moisture content - and as it dries out, it is nearly guaranteed to warp, a condition helped by being thoroughly nailed down, but not cured.....
I'd suggest going to a local-type lumber dealer (not a big-box) and ask them what they have available that is warp-resistant. You're not the first with that request.
Often, it's safe to build with the bottom framework board PT, and the rest regular lumber. Regular framing lumber is delivered dryer than PT, but not Texas-dry, so even it'll move around some. The daily temp fluctuations won't matter, most attics go through way more than 30 degrees daily, and survive. Another idea might be to use sturdy steel or aluminum angle or square tubing for the rails.
Russ

#4 Mary B

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Posted 23 November 2012 - 06:02 PM

I live in MN and summer temps can range from 60 at night with 100 degree highs the next day if a front goes through. My floor is all pressure treated rest is all standard lumber. My roof isn't a roll off though, it hinges open to each side. Insulated the interior as well as a house and interior temps stay cooler during the day.

#5 *skyguy*

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Posted 23 November 2012 - 06:34 PM

If you're really concerned with warping ... use kiln dried lumber (6%-8% moisture content) instead of green or air dried lumber. It's available at most lumber yards and Home Depot.

I used a triple 2x4 top plate to support the roof track in my ROR observatory and have never had a problem with warping.

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#6 David Pavlich

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Posted 23 November 2012 - 06:38 PM

My first recommendation is to make it at least 8X8. That's the size of mine and it's a squeeze with a C14 or a TEC140, for example.

I built the base with 2X8 treated lumber for the outside frame and the floor joists are treated 2X4s. The walls are outdoor sheets. The inner framework is made of standard 2X4s as are the roof joists. The roof is nothing more than roofing paper with metal roofing on top. I used that silver coated bubble insulation under the roof. The roof is made light so I don't have any problem rolling it.

The runouts are treated 4X4s and the uprights are 4X4 with a 2X8 treated end plate. The uprights are cemented into the ground. It's survived 3 hurricanes. And I can tell you with confidence that I have rudimentary carpentry skills. The one tool I recommend is one of these. This thing will save you a lot of time. Good luck!

David

#7 kpendlebury

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Posted 23 November 2012 - 09:13 PM

Thanks for all the advice!

I would love to build 8x8, but I'm dealing with fairly tight clearances. I'll see if I can get away with it though.

#8 Greyhaven

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Posted 24 November 2012 - 11:04 AM

Ken, I built an 8x10 ROR using the garage roller and track design I checked my 4x4's as best as I could for signs of twisting ect and still had one that holds the rollers develop a twist bad enough give me some amount of clearance problems after a few months I shimmed the wheel carriers but I'll have to replace at least 4' of that support this summer. The roof is operating fine but the twist looks like shoddy workmanship. We all have observatories that are smaller than we would like and I have no idea of your viewing equipment ect but 6' would require careful planning to make it practical. Your choice of useable space and viewable "space" should be considered. Please keep in mind that this advice is given by a guy with a twisted board and still thinks his observatory is the best astro investment he ever made.
Be Well
Grey

#9 csa/montana

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Posted 24 November 2012 - 11:14 AM

If you are using the inverted "V" metal track, with wheels that have a groove to follow the "V"; the v metal track is screwed down, and you are able to unscrew it to move it as the wood warps, in order to keep the track straight.

#10 Aircrftr

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Posted 24 November 2012 - 06:24 PM

Here is how I tackled the problem of maintaining straight tolerances in my roof system. I built the rails that the roof would roll on out of a sandwich of CCA 2 each 2x8x8"with 1" CCA treated plywood between them and 4"x4"x1/4" angle iron bolted to them to mount the inverted angle iron for the roof to roll on. Pic is worth a thousand words...

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#11 Aircrftr

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Posted 24 November 2012 - 06:27 PM

and the doodle art that shows how the track/roof was made to insure it would always be straight and no large open gaps between the roof and wall...

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#12 Aircrftr

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Posted 24 November 2012 - 06:28 PM

As built per plans...

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#13 Aircrftr

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Posted 24 November 2012 - 06:33 PM

As it looks mounted on the wall....

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#14 Aircrftr

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Posted 24 November 2012 - 06:35 PM

and to keep the roof square and rigid, here is a picture of the frame of the roof. I just built the trusses myself on the floor from a napkin plan and made a rigid square of the metal structure with tensioned cable. The roof is solid as a rock and never wobbles or racks when the garage door opener starts or stops.

Hope this helps stimulate the ideas :cool:

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#15 Aircrftr

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Posted 24 November 2012 - 06:42 PM

P.S. if you are wondering how I tensioned the cable, here is how. Just drilled a big bolt and double nutted it to be able to turn it and tighten it down to hold the tension.
(BTW, the cable is wound in the wrong direction in the picture.. I did wind it the proper direction after I took the pic.. LOL)

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#16 Aircrftr

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Posted 24 November 2012 - 06:43 PM

The other end..

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#17 Aircrftr

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Posted 24 November 2012 - 06:50 PM

The picture of the roof/wall rails gave the impression there was more clearance between them than it truly does. Here is a picture of the actual clearance between the roof assy. and the wall assy. after it was mounted on the wall...

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#18 Aircrftr

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Posted 24 November 2012 - 06:54 PM

Little view of how the roof rails are mounted for the roof to roll out on...

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#19 kpendlebury

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Posted 25 November 2012 - 09:12 PM

Aircrftr,

Thanks for all the pics! Unfortunately I don't have any direct access to welding equipment. Nonetheless, I appreciate all the effort you put into relaying your experience.

Ken






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