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Forum topic by sgreen posted 03-30-2015 09:16 PM 829 views 0 times favorited 14 replies Add to Favorites Watch
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sgreen

8 posts in 869 days


03-30-2015 09:16 PM

Topic tags/keywords: desk furniture modern maple plywood question

So I have come up with this L-shaped desk for the office and need some advice. The shape of the desk is represented in this picture .
The desk is 6’4” by 3’10”, the idea being to cut it out of a single sheet of plywood. The desk is built around the heater and other objects hence the 3’10” not 4’.

The idea for construction is to have a piece of 3/4” maple plywood cutout for the top with the same shape piece of 1/2” MDF glued and screwed to the bottom. The reason for the MDF is a cheap way to add thickness to the top. Then cap the ends with tan coloured 1 1/4” t-moulding like Rockler sells. .
The desk is supported by a cabinet and legs that are represented by the shapes on the table in this picture .
The 14” wide cabinet to the left is plywood construction and the legs are 2 3/8” diameter steel legs (Office desk type). The longest run of unsupported desktop is from the cabinet to the legs and is just under 5 feet.

My worry is that the desk will not hold enough weight (I have no idea what a desk should hold but at least a person standing on it). I don’t even know if the plywood alone could carry that weight without bending. I could either a) putting another leg on the long side which come in groups of 4 so I would have three extra at increased cost, or b) ditch the MDF and add 1/2” plywood instead at increased expense. I don’t know if adding the MDF is the best way for the thicker look for the desk because it is weighing down the plywood.

So can the plywood support all that weight without bending or am I asking to much of it? Would two sheets glued and screwed together be any better?

Thanks for your help!


14 replies so far

View Ghidrah's profile

Ghidrah

667 posts in 683 days


#1 posted 03-30-2015 09:59 PM

You may get some warping due to the uneven sandwich, probably better off with 2 layers of 3/4 ply. The degree of sag will depend on the amount of dead weight over a span, all things sag over time. The closer the supports are the shorter the span. Maybe you want the cab to act as a support along with the legs.

When I replaced the table on my RAS 20 yrs ago I sandwiched 5/8 flat stock on edge between 2 layers of MDF then glued and screwed together. Even though the table has slanted a few times over the yrs it has always remained flat.

-- I meant to do that!

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AandCstyle

2566 posts in 1718 days


#2 posted 03-30-2015 11:39 PM

You can look at the Sagulator to determine if the sag is beyond your tolerance. A possibility for you to consider is to glue a cleat to the back of the desk top as a stiffener. HTH

-- Art

View sgreen's profile

sgreen

8 posts in 869 days


#3 posted 03-30-2015 11:52 PM

Thanks Art. What a great resource. I put in fir plywood at 1 1/4” to give me some idea and it does say it’s acceptable at a 400lb total load. Deflection of .05 inches over 5 feet, which isn’t too bad for a desk.

View AlaskaGuy's profile

AlaskaGuy

2406 posts in 1770 days


#4 posted 03-31-2015 12:54 AM

If this desk is going up against a wall these work slick.

I do a lot of long computer counter tops where they don’t want legs and cabinets supporting the top so they can put the maxim number of chairs under them.

-- Alaskan's for Global warming!

View bondogaposis's profile

bondogaposis

4024 posts in 1812 days


#5 posted 03-31-2015 01:03 AM

I agree with the double plywood and skip the MDF. You could also run a 6” wide piece of plywood on edge across the back on the long span, that would add considerable stiffness. You could also add another leg there.

-- Bondo Gaposis

View sgreen's profile

sgreen

8 posts in 869 days


#6 posted 03-31-2015 01:25 AM

The desk is going up against a wall, but I want to stay away from wall mounted options. If I need to move it in the future it makes it a pain. I like the plywood on edge idea and another leg, but a the legs run 50$ for 4 so ordering another set for the one leg isn’t on my list of top things to do. I probably will go with two sheets of plywood vs the MDF and plywood though. Maybe run a 2” or 3” strip on edge near the back of the long side. Have to watch out for knee room though! Thanks again guys!

View Ghidrah's profile

Ghidrah

667 posts in 683 days


#7 posted 03-31-2015 03:10 AM

Not if you pocket screw the cleat to the back of the table.

-- I meant to do that!

View firefighterontheside's profile

firefighterontheside

13448 posts in 1317 days


#8 posted 03-31-2015 03:29 AM

I made a much larger U shaped desk for someone years ago. I used oak 3/4” ply laminated to 3/4” MDF as you had planned. Worked well. The desk had a 3/4” front as well. I ran a shelf about 16” above the floor and about 6” wide. From that shelf up to the top I put some blocks that basically served as brackets to help support the top. It was very strong and I believe the MDF would be fine. I recommend cutting one or the other a bit bigger than the other and then using a flush trim bit to make sure they are even when you go to install the edge band.

-- Bill M. "People change, walnut doesn't" by Gene.

View SawduztJunky's profile

SawduztJunky

35 posts in 619 days


#9 posted 03-31-2015 03:32 AM

-- I don't think I'm ever more "aware" than I am right after I hit my thumb with a hammer.

View iminmyshop's profile

iminmyshop

258 posts in 1455 days


#10 posted 03-31-2015 11:01 AM

You can make a large L shaped leg also out of plywood and place it off to the right side under the desk. I agree fully with using a double thickness of glued 3/4” ply for the top. The L shaped legs can be made of the same material and capped at the ends with solid wood. That would likely provide a more homey furniture look than steel legs. It will also provide more support and last longer. Further, The L can be angled i.e. does not have to parallel the back and right side.

View sgreen's profile

sgreen

8 posts in 869 days


#11 posted 03-31-2015 09:59 PM

What do you guys think of these table stiffeners. They would stop the sagging if any happened, similar to the plywood strip idea but with the benefit of being smaller and possibly stronger.

View AandCstyle's profile

AandCstyle

2566 posts in 1718 days


#12 posted 04-01-2015 01:14 AM



What do you guys think of these table stiffeners. They would stop the sagging if any happened, similar to the plywood strip idea but with the benefit of being smaller and possibly stronger.

- sgreen

If you think you need to go this route, go to your local hardware store and buy some angle iron or even channel iron for a lot less money. Of course, you will need to drill it and paint it. FWIW

-- Art

View iminmyshop's profile

iminmyshop

258 posts in 1455 days


#13 posted 04-01-2015 02:02 PM

With 2 layers of 3/4” ply glued you will have no perceptible sag even with a 200 lb person standing in the middle of the desk. Now if you and your best 200lb friend joins you in the middle and starts jumping, you might see a bit of sag but even then, probably not much. 1 1/2” ply is pretty darn strong.
Worst case scenario, you build it without the stiffener and add it later if you see a problem.

The sagulator mentioned by AandCstyle above is an excellent tool for providing this kind of information. You would have 1 1/2” of thickness with a solid wood edging. The “shelf span” is from the inside edge of wherever the boards are attached on either end.

Sagulator:
http://www.woodbin.com/calcs/sagulator.htm

View daddywoofdawg's profile

daddywoofdawg

1010 posts in 1036 days


#14 posted 04-01-2015 03:26 PM

You could build a torsion box desk,maybe cheaper and at least as strong and lighter,then the cleats or brackets in the wall.

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