DIY Frame Materials - Wide + Curved - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 10 Old 06-26-2019, 01:39 PM - Thread Starter
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DIY Frame Materials - Wide + Curved

I'm hoping to exceed 12 feet in width with my next build, which eliminates some of the more readily available products. I can't weld, yet anyway, but I am handy with woodworking and general mechanical engineering. The end product will be on a dedicated wall with sound treatment and fabric, so I can hide ugly construction. (Does not have to be a work of art unto itself) What should I be considering?

On the list so far:

Custom metalwork, by a local shop, for rolled steel or similar.

8020 or strut channel-type prefab metal parts

16 foot lumber, but what kind? How do I avoid severe seasonal effects?

PVC "lumber", which may not be sturdy enough.

gluing/laminating thinner strips of natural or synthetics
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post #2 of 10 Old 06-26-2019, 02:18 PM
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Are you looking for a AT Screen? What Format?


12' wide is certainly do-able. Ditto 13' & 14'. 15' to 16' is more problematical, both being wholly dependent on Screen Height (Format) and the method of Placement.


2 Spline-joined 7' long pieces of 8020 or similar will do....but so will a Frame made of carefully selected Kiln-Dried A-Grade Douglas Fir 2x4s (...if ya can get'em...)Being located on the East Cost would make that extremely iffy, unless you have access to a actual Lumber Distributor.


Again, Format choice and Mounting / Build considerations, and the type of material (screen surface) all have much to do/ say about what choices are viable

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post #3 of 10 Old 06-26-2019, 02:46 PM
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I think I would be looking at the 8020 MM is suggesting finding wood that length that is straight and will stay straight can be problematic. I'd be concerned on the "PVC Lumber" for two reasons its flexible when you get that long and its pretty heavy. If I was going to use wood i'd try and find some 5/4 poplar

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post #4 of 10 Old 06-26-2019, 06:11 PM - Thread Starter
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Test screen is 12 feet wide and made of finger jointed preprimed pine, which was ultimately too flexible, but i was going for a cheap test and underspecced it. It will be a stretched fabric for final screen, mostly likely. But for now I am worried about the frame materials. Not sure how/if I can bend 8020 to a 35 or 40 foot radius. If I could indeed get 4 pieces precurved and join them in pairs, that might work out great. Could be easy to attach masking to it if I get the right extrusion profile.

MM, you helped me paint the test, at 2.76:1 in light gray.

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post #5 of 10 Old 06-27-2019, 06:34 AM
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Scott,


Yes...I remember your ultra-wide project, and the quandary you initially had in painting it. You got'ter dun though.



To be assured that any curved wood Frame won't twist out of true, it needs to be blocked at the needed stress points. The radius you mentioned is pretty gentle, so after it's made, setting and attaching the center against Blocking then measuring and placing additional blocking 1/2 way out to the ends...and at each end should give you all the lasting rigidity and resistance against warp-age you'd need.


As to what "long length" lumber to use....now that's a bit more difficult to narrow down. It's a challenge to be sure! Certainly, a 16' 2x4 has enough bend-ability to give you the needed radius....you used 2x2 last time I believe.


Perhaps ripping 2x4s to 2x3 width would be a good intermediate solution.

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post #6 of 10 Old 07-01-2019, 05:45 AM
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If it were me, and maybe it will be one day, if looking for a material that is dimensionally stable and easy to work with I may not go any further than plywood.

Instead of bending the radius, I would be thinking about cutting out the radius from at least two layers of quality plywood laminated together with staggered seams. Without doing the math on arc depth for a 35' radius 12' long arc, let's say you have a 1 foot deep curve. With say a 6 inch deep plywood strip that's 18" or so and you could cut 3 or 4 such strips from a single sheet. Maybe my guesswork is off, point is material cost will be neigible.

After laminating a couple of strips together and cutting the curve, I'd sand it as close as I could to the desired profile (not that hard, I recently did this for the sides of 5 foot tall curved line array speakers). And then I'd finish the face with another strip of ply bent and glued along the curve. That would provide not only a very smooth curve, but add dimensional stability in an orthogonal direction. Depending on depth of the laminated ply strips and thickness of the bent face strip you could get some springback that tries to deform the curve. Going to 1/4" or 1/2" ply for the bent face would minimize this. Some experimenting may be needed to find necessary depth of the arc segments.
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post #7 of 10 Old 07-06-2019, 11:47 PM - Thread Starter
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Quote:
Originally Posted by Bigus View Post
If it were me, and maybe it will be one day, if looking for a material that is dimensionally stable and easy to work with I may not go any further than plywood.

Instead of bending the radius, I would be thinking about cutting out the radius from at least two layers of quality plywood laminated together with staggered seams. Without doing the math on arc depth for a 35' radius 12' long arc, let's say you have a 1 foot deep curve. With say a 6 inch deep plywood strip that's 18" or so and you could cut 3 or 4 such strips from a single sheet. Maybe my guesswork is off, point is material cost will be neigible.

After laminating a couple of strips together and cutting the curve, I'd sand it as close as I could to the desired profile (not that hard, I recently did this for the sides of 5 foot tall curved line array speakers). And then I'd finish the face with another strip of ply bent and glued along the curve. That would provide not only a very smooth curve, but add dimensional stability in an orthogonal direction. Depending on depth of the laminated ply strips and thickness of the bent face strip you could get some springback that tries to deform the curve. Going to 1/4" or 1/2" ply for the bent face would minimize this. Some experimenting may be needed to find necessary depth of the arc segments.
For some reason plywood never occurred to me. I had considered cutting the arc out of 2x12 or some such, and I have seen MDF used, but I didn't want to deal with MDF failing. I'll revisit the design and see if plywood helps. Thanks for the suggestion!
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post #8 of 10 Old 07-07-2019, 05:11 AM
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I built such a plywood frame many years ago cut from .5” 4 ply plywood and laminated 3 layers together glued and screwed. My frame was not curved but that wouldn’t be a problem to do. The frame I built was self tensioning from the inside out it is still hanging in my old house and is just as tight and straight as it was in 2006.

I have a thread about it but unfortunately the photo hosting site went down and I don’t know what happened to the original photos.

https://www.avsforum.com/forum/110-d...as-screen.html

It was a fun project and proof of concept that a laminated plywood frame is good way to go.

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post #9 of 10 Old 07-08-2019, 10:46 AM - Thread Starter
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I'm considering reorienting the room design to create a closed space, which will shrink my width down, potentially to 12 feet, getting me back in range of standard materials. I think rolled aluminum extrusion could still be a cool way to go, though, if I could find an affordable source. May be possible to make kits. I moved a desk made of plywood and pine lumber this weekend, and the weight or those materials was frightening.
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post #10 of 10 Old 07-15-2019, 10:42 PM
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Quote:
Originally Posted by ScottAvery View Post
I'm considering reorienting the room design to create a closed space, which will shrink my width down, potentially to 12 feet, getting me back in range of standard materials. I think rolled aluminum extrusion could still be a cool way to go, though, if I could find an affordable source. May be possible to make kits. I moved a desk made of plywood and pine lumber this weekend, and the weight or those materials was frightening.
1/2 plywood is about 40 lbs per sheet and it seems like two sheets would be more than enough, laminating two 8" wide strips to cut the top and bottom rails and dadoed 4" strips to make easily curved T pieces to give it strength once glued to cap each curve. They would look like wooden I-joists where one chord is curved. That would work for a 40' radius on a 12' wide screen (6" deep curve), but 12" strips would be needed for a 16' wide version (10" deep curve). With I-joist structure, chords front and back, you might get away without laminated the plywood, and just use a single layer and rely on the glued slotted chords to provide stiffness.



80 lbs does seem pretty heavy, but not too unmanageable for a single person. Especially since some of that weight (10 lbs?) would be removed when the curves are cut. More weight could be removed without hurting the structure in the wide pieces as long as there is 2"+ width remaining everywhere. Maybe just by perforating with a 1" drill in the wide areas.

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