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Discussion in 'Archived Threads 2001-2004' started by David_Merrow, Nov 10, 2001.
Is it ok to use wood other than MDF for a flexy rack? I like to make one out of oak.
I really don't see why the hell not. Oak is a hell of a lot stronger so there definitely won't be a problem with weight of equiptment. People us MDF for everything cuz its cost efficient.
Building shelves out of solid wood like oak can be problematic if you don't have a woodworking shop since you won't be able to find boards that are 20-24" wide. As far as strength goes, in an American Woodworker magazine article back in 1999, they recommended a shelf no wider than 22" between supports for 3/4" MDF for a load of 40-50lbs. OTOH, you can get by with a 36" shelf using a 3/4" hardwood for the same load.
So 3/4" MDF with supports 22" apart can only support 50 lbs? That seems very underrated to me.
I am making my rack out of a bunch of Cherry my Dad got for cheap...It is roughcut but he has a planer. He pretty much has a shop so when I go about making it I can do it right. We used MDF just recently to make a shelf and it doesn't seem like it would hold more than 50lbs at 22 inches. It's rather flexible stuff. It is pretty much just hardcore cardboard.
Initially that 22" MDF might look like it'll hold over 50lbs, but over time it'll eventually sag(aka creep). Since it doesn't have any grain, MDF has 1/4 of the strength of an average wood according to that article in American Woodworker. There are other ways to strengthen shelves though by adding additional pieces. By attaching a solid drop edge to the front of a shelf made out of MDF, it'll increase it's strength by ~60%. If you want an even stronger shelf, build a torsion box out of 1/4" plywood outer layers with solid wood runners in between and a solid wood front edge.
FWIW, the article was based on standards put out by the Composite Panel Association and the Composite Wood Council(www.pbmdf.com). The issue of the AW magaizine is Oct '99/#75 in case you're interested.
I remember when the article ran, I was surprised at the numbers given. For anyone interested, the article gives drawings of several methods to strengthen a shelf. Some suggestions are more complicated than others, but to support something heavy like a large TV, it may be the only way to do it.
If anyone has extreme requirements, they might screw a piece of L shaped angle iron under the front and rear edges, and then use an oversized lip on the front to hide the brace. A small size piece of aluminum might help, and be easier to work with.
My problem with this is that I've had this TV stand for 4 years:
With a 32" TV (about 120 lbs) on this stand, made of either 3/4" or 1" MDF, it could last a lifetime without budging. And it's only supported on the back end about 2". I can't imagine this stuff ever bending even under twice the weight.
Well that link didn't work...session timed out. I will offer up my own anectdotal evidence to refute your claim though. I have an entertainment center made out of 3/4" MDF that has sagged over time since I bought it 8 years ago. The top shelf in particular is convincing that MDF is a poor material since it's never had more than 40lbs on it and has sagged noticeably even though it's supported in 3 places over a 48" span. The 25" TV sits on a shelf that's supported in 3 spots over a 28" span and it's sagged to the point where the doors underneath won't close.
A new entertainment center is on my to do list since I got into woodworking almost 4 years ago. I'm thinking of using 5/4 red or white oak for the one I make, but then I usually over engineer the projects I design and build. You should see the bracing underneath the 24"x40" tile top coffee table I built with it's 3/4" MDF substrate.
Perhaps we're talking about different materials. There's plywood, MDF, chipboard, pressboard, etc. If we're talking about painted surfaces, how can we be certain it was MDF? I know that the unit I mentioned is MDF only because when I bought it, the box was damaged and a shelf was broken in half. There was no grain or pieces to the wood, just looked like what it was - sawdust and glue.
When I broke my cheap nightstand a few years back, it was pressboard or chipboard, it splitered off and you could see small pieces of wood pressed together.
In my case it was one of those typical you-put-it-together-yourself kits, and there were many unfinished edges exposed that were covered up once you assembled all of the pieces.