Building a desk with 4 x 8 sheet of plywood


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Old 07-08-15, 03:39 PM
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Building a desk with 4 x 8 sheet of plywood

hello wood/physics savants,
I'd like to make a very large desk by just using a 4 x 8 sheet of plywood. I'm planning on using hairpin legs, nothing fancy. My question is whether I need to gird (maybe not the right word?) or support the plywood by reinforcing it underneath. I have some 2 x 4s I could use underneath so the plywood is supported, but I truly hate the clunky way that will make the edges look. I'm really hoping to keep it looking as simple and clean as possible. Will I end up with a sagging/bowed desk if I just use 4 hairpin legs? If so, is there a way to support it that's a little more subtle? Any ideas?
 
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Old 07-08-15, 04:01 PM
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You didn't say how thick the plywood is. Obviously, some will sag more than others. There are some vinyl 1x4s that won't look so "chunky" as the 2x4s will for support. May I ask why you want such a large desk?
 
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Old 07-08-15, 04:05 PM
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Hi Alma1 and welcome to the forum.
First let me ask if you really want this to be 4' deep as while sitting st the desk, 4' would be an impossible reach?

Then, how thick is your plywood and does it have a finished surface at least on the top?
But, even a nice piece of 3/4" plywood will sag if only supported at the 4 corners. Even with 2x4's on edge set under the edge a few inches will not allow someone to sit on the edge.

But you are in luck as there are some great wood workers on the forum (not myself) and they should be able to guide you.

One quick thought if money is available, a perimeter (set in a couple of inches) of box steel might be less visible and provide the support you need.

Bud
 
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Old 07-09-15, 03:28 AM
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It would be nice to know more about your intended desk design. What type of legs, any cabinetry or drawers below? just a 4x8 rectangle or do you plan to cut it to fit? The edges of the plywood can be dressed up with trim to hide the plywood edge.
 
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Old 07-09-15, 06:20 AM
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As already mentioned, a piece of plywood will most certainly sag. Generally a desk like that will need a framework (picture a ladder made of 1x4's) directly under the top. Legs are sometimes bolted (with at least 3 bolts) into the corners of this framework from each side. They also make corner brackets that can be used to attach the legs and reinforce the corners. If the desk will be loaded with a lot of heavy stuff, 1x6's would provide a stronger framework for the top. Tabletop fasteners can be countersunk into the top of the framework and are one way that the top can be fastened with screws from underneath.

As marksr mentioned, plywood also needs a facing of some type on the edges, either solid wood or rubber/plastic t-moulding. I agree that 4' is kind of big for a desk.
 
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Old 07-09-15, 07:40 AM
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Thanks so much for all your replies! The plywood is 3/4 and it does have a finished top. The reason I want such a big desk is because i work on really large paintings/pieces of paper, often several projects at once.
 
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Old 07-09-15, 07:43 AM
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I wasn't going to add any drawers or anything below, just use the plywood as a desktop, and I was hoping to use hairpin legs, since I like the way they look and they also seem pretty easy to attach...
 
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Old 07-09-15, 08:12 AM
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3/4" is good, but even that, at 8' will eventually sag, especially if any weight is left on top.

Now, knowing that still allows you to go ahead with just the plywood and an edge strip for finish. But locate the legs so that, IF it does sag and you want to correct it, you can add additional support at a later date.

In college we had tiltable drawing boards that allowed us to work flat or at an angle for large drawings, blueprint style.

Bud
 
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Old 07-09-15, 10:14 AM
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IMO it's always a good idea to have 1xs under the plywood to stiffen it up and help prevent any sagging.
 
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Old 07-09-15, 10:23 AM
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Old 07-10-15, 04:13 AM
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Thanks everyone! So helpful!
 
 

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