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RoR - Sizing gantry materials

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#1 SteveInNZ


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Posted 13 March 2018 - 05:06 PM

I'm looking at options for the gantry part of a RoR shed conversion but I don't know how to compare them.

"I did this, that or the other" seems to be very hit and miss and I'd prefer a more engineered approach. For example, John Stephen Hicks rolls a 16ft roof on a double 2"x6" top plate sitting on a 2"x8" joist with a mid support while SkyShed uses a single 4"x4" spruce beam with just the end support.


I'd also like to at least consider options less prone to warping like glulam, steel, aluminium or any other suggestions.


My shed is 4mx3m (10' x 14') and the roof assembly weighs 146kg (322lb). I haven't decided if I'm going to roll off the full 4m or just 3m (leaving the roof over the warm room).


I'm leaning towards gate roller and track. Are there any pros/cons of 'U' vs 'V' profile ?



#2 retina boy

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Posted 03 April 2018 - 06:09 PM

The part you really want answered, calculations on gantry design, I am not going to be able to help you on.  However, I can offer some observations. 


1. Using dimensional lumber is just not a good idea.  Unless you have a stash of well aged, dried lumber that you are sure will not move, dimensional lumber will warp. There are so many other good options that I think you should consider something else.  Your other considerations are all good ones and will work.  We have 4x6 beams with center and end posts to support our 20x24' roof.  This is plenty strong.  We have a floating piece of angle iron on the top as the track for the rollers.  When one of the beam sections, 8' long, warped, the angle iron was sufficient to hold up the roof!  There probably can be much less material in the support structure than we think.  Around here, the builders have largely abandoned wood for the gantry and use 2"x2" angle iron for the rails and with one 2" post at the end and X bracing on the posts.  All have been very steady with no deflection. 


2.  I just do not think that people have gone through the calculations to determine the appropriate sized material for the gantry and are instead relying on the "more than big enough" approach.  If you did the deflection calculations for angle iron, I bet you would find that you need much less than we all use.  Most of use do not even know the weight of our roofs. 


3. It is useful for at least on side of the roof track to be able to shift on its own.  This allows the track to compensate for changes in the roof dimension and prevents binding. 



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#3 *skyguy*



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Posted 03 April 2018 - 09:20 PM

I built the track and supporting framework for my garage-top ROR using 2" steel tubing and 2"x2" steel angle iron. There's just a single end support and the entire structure was welded together. The square tubing was used for the track and inverted angle iron was spot welded on top for the cast iron v-groove wheels. The observatory was built 17 years ago and ROR operates as easily today as it did on its first day with no repairs and only an occasional paint touch-up. 


OrbitJet Observatory pictures:




Observatory Track.jpg

#4 Dustin Smith

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Posted 03 April 2018 - 09:33 PM

I used 4x8 gluelam beams for mine. My ROR build is on my website, see my signature below if interested.



#5 Richard Whalen

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Posted 03 April 2018 - 11:39 PM

Im using aluminum square and rectangular tubing that is used for pool roof supports. Easy to connect, light, stiff and strong. Mine will slide on teflon plastic, in L beams, no rollers for a positive seal, no leaks or bugs. 

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