Design question

[Salty]

I would like to modify my current computer desk to look something like the picture below, with some variations.
My question is, how would you support the center to prevent it from sagging?
My current desk sags badly, mainly because it is particle board.
I'm considering chopping it into sections and putting on a new top to make a corner unit.
In this image, the right hand upper section is not directly over the base unit and I'd be concerned that it would eventually begin to look like a sway back horse.
Would 3/4" plywood bulkheads support it?

Thanks.

[TheRic]

I'm no expert on building this stuff. From the ones I have put together, they are usually MDF. And as for the sag, they don't care if it sags a year later, they already have your money.

It depends on how much weight you are talking about putting on the upper shelves. To help figure out sag, go to the sagulator here:
http://www.woodbin.com/calcs/sagulator.htm

If you are worried about it sagging, design it a little different. Move the top over more, or the bottom over, or both. Instead of the bottom inside wall being square, angle it back. Will give more support, and more room in the back for wires, plug strips, etc.

From the picture I would also say the left hand is offset by about the same amount.

[cwsmith]

I'd put a wood brace to run from the inside back corners of the left and right lower shelf modules. Probably use a 1 x 3 or 1 x 4, preferably hard wood, but even pine would do. It would run from the two corners, mentioned above and cross directly behind the keyboard drawer. By the looks of the picture, that would act like and extened back board on the keyboard housing and would probably come close to being fairly center under the table top.

I'd probably also had a hardwood trim (1 x 2) across the front of the table top, with the keyboard tray just underneath it.

Someday, I'll figure out how to post a picture on this site... then I could illustrate what I mean - sorry!

CWS

[drumpriest]

My computer desk features a mortise and tenon frame between the cabinets to support the top, my keyboard drawer slides out from under it. My LCD is on a small riser which creates the perfect ergo set of numbers. I based my entire desk design around measurements of how I sit. I doubt this thing will ever sag. I had a 19" NEC (80 lbs) on it for about a year, no budging at all. The frame doesn't have to be huge to add a ton of strength.

[LarryG]

As I read through your query, the very first thing that popped into my mind was, as it turned out, exactly what CWS described: an apron located just behind the keyboard drawer, roughly midway front-to-back of the top.

If you're going to build a new top, another thing you could do is sandwich two sheets of 1/2" plywood together. A 1" top will be considerably stiffer than 3/4" and will look better to boot. On a piece of furniture this large, a 3/4" top is visually weak (too thin); a 1" thick top will have better proportions.

[cabinetman]

There are a few options to this dilemma. My initial design would try to get the weight of the wing cabinets over the base cabinets. Next, as mentioned a cross brace behind the keyboard drawer. But that alone won't deflect the weight at the front edge.

I would try to put a full back on both the upper cabinet and the kneehole area which would take the stresses out of the rear sections. For the top, I would double up 3/4" for a 1 1/2" top (the bottom sheet could be any 3/4" plywood). The top piece would be of the specie of the finish intended. Then I would install to the front edge 1 1/2" hardwood edging.



YOU HAVEN'T FAILED, YOU JUST HAVEN'T FINISHED

[jziegler]

I built a corner desk this summer based on a design from Woodworker's Journal from 2001 (I think). It has a similar overall layout, without the top section. To support the corner, it's a built in unit. It has braces along the edges of the corner against the walls. They also serve as cord channels to get the wire up off the floor. Made from 3 pieces of 1x3 or 1x4 poplar I think. Of course, it requires that the new top fit all teh way into the corner.

Let me know if I need to clarify, you want some pictures, anything like that. I never got to posting anything in finished projects because I still have some more work to do on it.

Jim

[scorrpio]

That upper shelf looks like it should give the whole unit enough rigidity to eliminate sag. I mean, draw a mental picture. If the table sags, the side sections should lean into the center, 'squishing' the top shelf section. And it should not squish.

[LarryG]

The upper center shelf may not squish, but it definitely won't prevent the top from sagging. The side units to which it is attached have solid backs but are open at the front; nothing to prevent racking there. There'll also be a tendency to pull the connections apart where the upper center shelf attaches to the side units.

[Salty]

Now there is a lot of realy great information and suggestions.
Thanks to all for your responses.
I like the 1" or 1-1/2" thick top ideas.
I will need to rethink this whole process again.
I failed to mention that I want this to be modular enough to take apart in sections so it is easily moved out of the basement.
That has been the downfall of this current desk in that it has been moved twice and each time it seems to get worse.
There really isn't any support on these things. They give you pieces of cardboard to nail onto the back but it doesn't cover the entire back surface and is not supportive anyway...it's cardboard!
The sketch below is the design of my current desk. The blue section is the main support. The problem with that is that it is at the back of the desk and does little to support the front.
Also, I don't like putting the mid-tower case on the floor and there isn't enough space under the shelf sections for it. So, I have the 17" monitor and the tower both in the center section, and it's a tight fit.
I'll come up with something...eventually. Or I'll just design and build one that suits me better.
Thanks again all.

[LarryG]

The blue section is the main support. The problem with that is that it is at the back of the desk and does little to support the front.

What CWS and I were saying is that if the blue piece could be moved out about half the depth of the countertop, it would stiffen the top (especially a new, thicker top) sufficiently that you could get away without having anything at the extreme front or rear. This assumes that the depth of the countertop is in the usual 24" to 30" range for these things, so that the blue piece would be located 12" to 15" from either edge.

Obviously this means the keyboard drawer would have to shallow enough, front to rear, to allow such an arrangement. Keyboard drawers are usually not more than about a foot deep so this might work as-is, or you might be able to cut down the KB drawer enough to make it work.

[Tom Miller]

Another +1 on the cross-brace just behind the keyboard tray -- that's the first thing I thought of, too, before reading everyone else's posts. If the rib is no taller than the keyboard tray is deep, it shouldn't interfere with your knees when sitting.

Keep in mind, though, that the #1 fix is to replace the thin piece of particle board with just about anything else.

Also, consider a 1.25" - 1.5" tall solid wood edging on the front of the top surface. This'll stiffen up the very front.

Regards,
Tom