Revolve Framing

[DRU]

Looking to build a pair of 8' diameter turntables. I want them to easy to transport, so I was thinking of having them break into two 8'x4' semi-circles or four 4'x4' quarter circles (1-2 people should be able to move it from storage). I was thinking of building them stress skin style with 1/2" ply top and bottom with 2x4 on face as the framing, making the overall height 3". It would support basic flats and platforms and up to 8 actors. I will worry about turning it later.

1. Is a 1/2" ply top and bottom strong enough with the framing every 2'? Or should I go up to 5/8" ply?

2. Break it down to two pieces or four?

3. I'm going to make a caster bed with the casters up. If the casters are spaced in concentric rings 2' apart, and each caster in each ring is no more than 2' from the next in the same ring, will that be enough support? Is it too much or too little?

4. Anything I'm missing?

 

[BillConnerFASTC]

2' on center framing and I'd worry about 3/4" ply and the concentrated loads at the casters. I know no place a where 5/8" ply on 2' centers is satisfactory for any floor load. Doesn't work in a bedroom let alone on a stage. But why not real stressed skin with 1 1/2" foam between 3/8" ply?

 

[Colin]

I would use the foam method like Bill says for the best combination of lightness, strength and ease of building the curved edge. But at least use 5/4 instead of 2x. If you can get 5/4, the quality will probably be higher than 2x, and it is all-around easier to work with. At least in my area, I'd have to hand pick 2x4 for a good 45 minutes to with some luck find enough straight boards for building triscuits, which require a very flat gluing surface between frame and skin.

My recollection of the "Yale method" is 5/4 framing at 2' with 5/8" ply, good for 50psf (L/240? don't take my word for it) when assembled correctly and supported by studwall every 2', which is different than putting it on casters every 2'. With studwalls oriented correctly under a triscuit, each framing member crosses all the studwalls, and the studwalls run perpendicular to the plywood grain. With caster-up, you don't have that support and control since the platform frame and grain moves in relation to its support, and that support is relatively tiny caster points. You could hypothetically wind up loading small points of un-framed plywood and not much else. I guess if you use a ton of casters you can mitigate that, but I don't know about correct spacing.

It seems like on a turntable you'd want to be extra careful to stay away from any deflection since the platform is floating on casters and not fully secured to the deck. Although with 2' caster spacing you never approach much of a span for deflection... Anyway, wiggles would seem to invite noise and fit issues. I guess that would depend on how the load is distributed, and how those eight people move on the platform. Also how well the turntable is locked in playing position, or does it do live moves like a carousel or something?

Definitely minimize seams that will roll over casters by making them in two pieces not four.

 

[Colin]

Oh hang on, I said 2' frame spacing but it should be 1'. I've never seen anything but 1' for stressed skin.

 

[BillConnerFASTC]

Different stress skin being discussed. I was not clear, but was thinking only foam, no solid web. But Colin's method - only solid webs - could work and may be easier. Gluing foam is harder. And I agree strongly - not framing lumber like SPF 2 by. 5/4 or even one by - did that at Yale pre - triscuit - ban work. With the right "bearing" just perimeter framing for casters, "spoke" framing, and two half circles could work slick.

 

[DRU]

As a thought: would 16g 1x1 work just as well as the framing, replacing 5/4? Still have a bottom skin, spoke style framing, 5/8" ply skins. I have some extra steel, which is why I ask. Seems like overkill. The texas triscuit uses 1-1/2" 16g box tube, but would the bottom skin increase the strength to compensate?

 

[bobgaggle]

I built a 16' revolve with 1x1 16 ga tube. It had a 3/4" deck and was open underneath except for 3/4" ply rings to ride on the casters. Never had an issue with noticeable deflection. Max distance between the framing was 24". It broke into three pieces for transport and was bolted together through the steel. The bottom rings were added after it was bolted and covered the seams

 

[BillConnerFASTC]

I built a 16' revolve with 1x1 16 ga tube. It had a 3/4" deck and was open underneath except for 3/4" ply rings to ride on the casters. Never had an issue with noticeable deflection. Max distance between the framing was 24". It broke into three pieces for transport and was bolted together through the steel. The bottom rings were added after it was bolted and covered the seams

3/4" ply on 24" centers is probably fine but how close are the caster rings, which determine the framing span? And is their framing behind the caster rings? A lot of important details.

 

[bobgaggle]

Been a while since I saw it. I want to say there were four rings, which would make it a 2' distance, 4' across the center, but that was supported by the pillow block and shaft. And I want to say each ring was 6" wide, with framing under each edge (we had a roll bender so it was pretty easy to make the framing support consistent) I suppose it would have been better to put steel directly under (or over i guess) the caster, rather than bridging the gap with the ply ring and the caster rolling in the middle of the ply, 3" from the nearest steel.

 

[BillConnerFASTC]

Sounds like in the ballpark of 70 casters. Sounds like a good design. I thought the op might be looking for something simpler.

 

[lwinters630]

Here is a link to plans from VAN for revolves. I found them very useful.

http://www.controlbooth.com/search/998024/?q=Revolve+plans&o=relevance&c[node]=30&c[user][0]=1880