Quick ?, MDF or birch ply?


Building a couple corner computer desks for the SWMBO and I. Plans call for MDF with laminate on both top and bottom for Tops (American Woodworker, Oct), but I have 3/4 birch ply on hand and think it might have less sag over time without the bottom laminate and 2 coats of finish. I've never put laminate on the bottom of anything I've built and never had a problem, I put several coats of finish to seal the wood.
So what I'm wondering, over time will MDF or Birch ply sag more? The only weight on back section will be the monitor, yeah we're still with crt's. Those lcd flat screens sure look nice, but, I was happy with my Radio Shack Model I.
I did a few different things on this desk and will post when about finished on abpw. If anyone else is building this desk I hope you show us what you are doing.
Al in WA
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Al wrote:

No experience but I'd have a lot more faith in plywood than MDF.
MDF is flatter, heavier, and it may damp out vibrartions better.
--

FF


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I haven't seen the plans, but from past experience, I think that the birch ply is a better choice. If the span is 24-30 inches, you have nothing to worry about. If in doubt, run a couple of strips of the ply underneath and thn double up on the edge detail so it looks like 1.5 inches.
I still have a CRT monitor too, so don't despair.
Lou
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[snipperized]

Why not use particle board? Cheap, flat, and get the 1" thick stuff. Laminate the edge, forget about the bottom.
The stuff don't flex much either.
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On Thu, 06 Oct 2005 22:15:58 -0400, Robatoy wrote:

I scrounged a 72 x 30 in particle board desktop. It's supported at the corners and rear center and has a lip underneath all around. It holds two computers, three monitors, random peripherals, and a small TV. It sags. I'm not disagreeing with Robatoy, but OP might want to think about good cross support.
--
"Keep your ass behind you"
vladimir a t mad scientist com
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Australopithicus wrote, yet did not archive: "OP might want to think about good cross support." Agreed. Tom
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Cross supports are good. If you put in enough of those, the top can be made from 1/8" hard board *G*
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Devils advocate here, MDF laminate both sides, makes a really nice finished product and frankly you'll be amazed at how rigid it will turn out. I made a similar work center for a pals college student. I used 1" mdf bisquited on an inch of red oak laminated over the oak on both sides an ran a 1/2" roundover for a bullnose finish. The kneehole had a 40" span and I could jump up and down on the thing with my 300# self and it deflect about 1/8". No sag no way...
Knothead
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I built a corner desk by laminating a sheet of birch ply and MDO ply. I also used two legs and wall cleats. It doesn't sag.
Pictures here: http://www.clsid.com/nsw/desk /
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Knothead wrote:

I find that most computer desks are too high--I wanted the area above my knees to be an inch thick, max.
It also had to span 4 feet over my knees, and couldn't have any supports for 18" from the front of the desk. The main surface was designed to hold 3 21" CRTs, at around 80 pounds each.
I've seen really nice commercial desks using 1" HDF over a steel frame (http://biomorphdesk.com/1-888-302-DESK/multi/overview.html ) but I couldn't source HDF that thick.
I found a 1" sheet of plywood that had surprisingly decent faces, edged it with a few inches of solid wood, and ran a 2x6 on end lengthwise under it a few inches past where my knees go.
It's pretty solid.
Chris
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For laminate, MDF is the best substrate on surfaces that aren't exposed to moisture. Best bet is to have it on a 3/4" plywood ladder frame, esp under areas that you would place heavy items.
You would need very good A-C plywood to keep any irrgularities from telegraphing through the laminate. I would save the birch for something nicer.
-Matt
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