Large Broadway Flats

[nobl13]

Hey all, I just got the plans for our next production, and the designer wants 8' 4" x 20' flats that hinge. I'm thinking Broadway flats with aircraft cable to prevent sagging. The largest I have ever built was 8' x 7', but those held up pretty well using 5/4" for framing, but I think it will scale. Has anybody else tried something like this?

 

[JChenault]

Back in the day ( when you could get straight lumber ) I made lot of 20 foot broadway flats. We used 1x4 not 1x3 for this size, but asside from that no issues, not sure what you mean by using aircraft cable.

 

[kicknargel]

If you can get good 5/4, that's probably best. Could also consider a finger-jointed material, since it tends to be nice and straight. Or I bet you could get clever with building broadways out of hog's trough for stiffness.

 

[StradivariusBone]

not sure what you mean by using aircraft cable.

Perhaps a diagonal? Like these things do for wooden gates? http://www.amazon.com/dp/B00004Z109/?tag=controlbooth-20

 

[JChenault]

Perhaps a diagonal? Like these things do for wooden gates? Amazon.com: Stanley Hardware 76-0828 Anti-Sag Gate Kit: Home Improvement

But that's what corner blocks are for. If he is worried about keeping it square, add in a diagonal brace as part of the framing.

 

[gafftapegreenia]

Find an old school stagecraft text. Corner blocks and keystones on the toggles with cinched nails AND mortise and tenon diagonals and toggles. Not that I'm really saying to build it that way, more so that you might find inspiration in the old ways.


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[Robert]

An old school solution to building manageable tall flats to was to cut a taper on the inside of the stile so that the top of the flat was lighter then the bottom. The next thing you might need to practice is a scarf joint to make longer pieces of lumber.
I would probably use kick's suggestion and add a stiffener to the frame. Are these hard or soft covered? For hard covered you might want to consider tubular steel.

 

[StradivariusBone]

But that's what corner blocks are for. If he is worried about keeping it square, add in a diagonal brace as part of the framing.

I agree, I was just guessing for the use of aircraft cable.

 

[gafftaper]

A community theater in the area here uses slotted Unistrut across the top of all their sets to keep the walls straight and stiff. A piece of 1x2 fits perfectly in the middle of the Unistrut, then screw through the front of the flat, through the slotted side of the strut, and into the 1x2. This will sandwich the strut between the flat and the 1x2. Works great. It would cost a bit, but you could use a similar technique to make some strong giant flats.

 

[kicknargel]

Mortise and tenon is totally overkill, but any broadway flat must have diagonal framing members, one high and one low, in opposite orientation. Corner blocks and keystones are not sufficient to keep it square, but they are sufficient to hold the frame together. As mentioned, check a textbook.

 

[derekleffew]

... but any broadway flat must have diagonal framing members, one high and one low, in opposite orientation. ...

Nope. Both diagonals (cornerbrace, in illustration below) should be on the SAME stile.

 

[gafftapegreenia]

Nope. Both diagonals (cornerbrace, in illustration below) should be on the SAME stile.

So, why?

 

[gafftapegreenia]

Mortise and tenon is totally overkill,

Oh its totally over kill, but it will be the strongest flat you'll ever build.

I had to trash some old moldy Broadway flats a few years back, and they were nearly indestructible.

 

[kicknargel]

Yes, on the same stile, in opposite orientation. One up to the left, one up to the right. This is because the joints are much stronger in compression than tension, so you want one in compression for each direction of "squish" of the parallelogram.