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Old 05-11-2015, 04:47 PM   #71
Dia
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Re: Lola, The Petroleum Falcon

Quote:
Originally Posted by rallypanam
If you are looking for cheap and easy, how come you don't just use a sheet of plywood?
I'm nervous that just plywood, even the good stuff, will be too prone to catastrophic failure. If the bed breaks and we fall, we'll fall onto our son who will be sleeping below. We're looking at north of 350 lbs up there, before bedding.

Is a simple sheet of good plywood really enough?

Also, the 2x10s are cheaper than the plywood.
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Old 05-11-2015, 05:18 PM   #72
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Re: Lola, The Petroleum Falcon

3/4 ply is what SMB uses. It's strong stuff. They use 3/4 plus a 3" foam mattress, upholstered. That's it. Different years could be different but most I've seen are like this.
Think of it this way. Every adult couple has somewhere in that same ballpark of weight up there, some probably a lot more.

I'd still get an air ratchet if you have an air compressor.

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Old 05-11-2015, 07:44 PM   #73
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Re: Lola, The Petroleum Falcon

Still pricing stuff...

Hardwood plywood around here is $40 - $60/sheet, and that's NOT for marine or Baltic birch. If I go with marine or Baltic, it's going to be more than double the price of the 2x10s.

Is hardwood plywood good enough, or do I really need the marine / Baltic stuff?
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Old 05-11-2015, 07:45 PM   #74
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Re: Lola, The Petroleum Falcon

The bed platform in my '97 gradually failed as a 250# friend slept on it during the course of a trip. Ultimately it tore itself apart, ripping the fabric and "ejecting" the footman loops that held it to the ceiling (because they were screwed into a joint that came apart). The bed didn't come crashing down (although it would have eventually) but rather went from being flat to being shaped like a long "chute" with my friend lying in the trough.

The way it was made originally, was with a single 3/4" of plywood, plus a perimeter band of ~3" wide 3/4" plywood. The band was just stapled to the main piece, and so when the bed was stressed (it had never been used by the original owners so was "new" when I started with it) the staples simply came apart and the perimeter band was no longer doing anything - hence the bed "tacoed." So from that I would say a plain sheet of 3/4" plywood would not be enough (although a really good grade of ply, something like Apple Ply would stand a better chance).

Since were were in the middle of a trip, we took the bed platform apart on a campground picnic table, and reattached the perimeter strip with glue and plenty of screws. That made it much better than new, but it's still probably not a method I would use if starting from scratch. It's rather heavy for the strength you get (van may be light, but you still get to heft bed when using ceiling support straps). OTOH, it's simple and fast.

Basically, with any of these skinned systems or even the one I had, you are gaining strength by bonding various pieces together. That's why my bed failed when the perimeter strip came detached. Suddenly two "sticks" were just two sticks, vs. the intended "bundle of sticks," which is much stronger.

As was mentioned, the sandwich of thin-skin/core/thin-skin does need its bottom skin, because it is a tension sandwich. Take away the lower piece of bread (skin) and you no longer have a sandwich, but rather just pieces of wood that are too thin to work alone.

In boats, sandwich/tension construction is often used for decks and bulkheads because it is light and strong and not too thick for that strength, so it is a good way to go. But it's not as easy as just lobbing a sheet of ply up there. If you do go with the "lob" method, I'd at least add a glued/screwed perimeter strip like mine had (well, like mine had after we glued and screwed it). You can use something as simple as carpenters wood glue - we did it based on one trip to Wal-Mart and a campground picnic table It's not as light, nor as strong as a skin/sandwich, but the bed stayed flat and bonded together for the rest of the trip. To visualize what the perimeter strip helps do, think of a thin bookshelf sagging in the middle under load, and then the vast improvement of putting something like a 1 x 2 on edge along the front edge of the shelf.
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Old 05-11-2015, 07:52 PM   #75
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Re: Lola, The Petroleum Falcon

Thanks, Viva!

As clunky as they are, I may stick with 2x10s. At least then I'm not worried about strength.
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Old 05-11-2015, 08:39 PM   #76
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Re: Lola, The Petroleum Falcon

Quote:
Originally Posted by Dia

Is hardwood plywood good enough, or do I really need the marine / Baltic stuff?
No need at all. Get the cheaper hardwood stuff. It's fine. Marine is only needed for wet applications, which I hope you don't have. Baltic birch is lighter, but certainly not necessary IMO, especially since you're probably going to cover it up.

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Old 05-11-2015, 08:48 PM   #77
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Re: Lola, The Petroleum Falcon

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Originally Posted by Dia
Thanks, Viva!

As clunky as they are, I may stick with 2x10s. At least then I'm not worried about strength.
Although, they still may be too bendy (but heavy and clunky). But maybe I need to go back and read about how you would use the 2 x 10's. But if you just lob them up there they are going to be fairly bendy. They would need to be attached together to present a united front, and even then.... yeah, I don't like the sound of it.

If you do want to use "boards" instead of plywood, maybe do something more along the lines of 1 x 2 slats with angles to provide stiffness around the perimeter?.... maybe... (just thinking out loud). The angles could turn upward and the mattress should keep you from scraping across them. I'm just thinking you want to keep it as thin as possible (since there is no excess of room under the top when it's down). Of course that still leaves the middle rather unsupported, so maybe scratch that idea. It's that wanting it to be thin that makes many "normal" ways of stiffening not work.

Plywood with a "border" glued and screwed on (the border is on top of the main piece, under the mattress but you can't feel it in actual use) still seems like a better/easy way to get strong but thin. Skinned box frame even better but not as easy. You can get Home Depot or Lowe's to cut plywood for you to a pretty exact dimension if tools are a problem.

I've built many bed platforms out of 1 x 2's and 2 x 4's back in the day, but they didn't need to be thin so I was easily able to support the slats.
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Old 05-11-2015, 09:05 PM   #78
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Re: Lola, The Petroleum Falcon

Re: 2x10s - what about something like this screwed to the underside to keep them all together?

http://www.homedepot.com/p/Everbilt-1-3 ... ord=584328



Re: bendiness - found this video. His first test is at 4 ft, 9 inches longer than the span I'm contemplating. Interesting. Guess I'll have to go play with some lumber.

[youtube:mhemnzz3]
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Old 05-11-2015, 09:20 PM   #79
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Re: Lola, The Petroleum Falcon

Now, I could be wrong, but the problem as I see it is that you just keep adding "flat" material (vs. material on edge which is stronger). But of course you're trying to keep it as shallow as possible so you can't add things like 1 x 2's on edge. That brace would keep the slats together, which will add some benefit, but I still think the whole shebang may still be too bendy (i.e. they will taco in the middle). Seems like much bulk and weight as compared to rigidity imparted. Let's see what anyone else thinks.
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Old 05-11-2015, 11:26 PM   #80
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Re: Lola, The Petroleum Falcon

Quote:
Originally Posted by Dia
Thanks, Viva!

As clunky as they are, I may stick with 2x10s. At least then I'm not worried about strength.
You better do the math - that sounds too heavy... we are talking about your Penthouse bed, correct?

If so, you need to see how thick it can be when the top is down - not much room.

I'd stick with plywood - lighter and it is stronger in the same thickness. It is also easier in that all you have to do is get it cut to size - nothing to glue or screw together...
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