18mm mdf over a 1200mm span

[markblue777]

Hi All,
I am going to build a little desk for the computer and was wondering if I would receive any bowing from 18mm mdf over a 1200mm span.

the main desk unit will look like this

as you can see simply construction, it will a little unit to that sits under the right hand side but will not have any contact with the main table structure so no support offered by it.

the desk and legs are 600mm deep so not sure if that would make much of a difference with regards to sagging.

The weight on the table will only be keyboard, mouse, small speakers and probably a book or 2 as I will be mounting the monitors to the wall.

Cheers
Mark

 

[Mar_mite]

Yes mate, that will sag. Is there a way of attaching a rail to the underside? Do you have the leg room?

 

[markblue777]

hmm well i would be able to do a 25mm square support i think but i would have to redesign the unit that sits under the desk on the right hand side so it sits 25 mm lower. not a mega lose so should be fine really

Cheers
Mark

 

[=Adam=]

I don't think a 25mm square rail will be of much benefit to you. It will be better than nothing but ultimately you will have sag.

Ultimately it all depends on where you place the computer, the closer to the centre = more sag as the maximum bending moment of any member occurs at the centre point. If it is possible to place the computer closer to one side then this should help to reduce the sag.

I hope this helps?

 

[mailee]

ideally you would need at least a 2" apron front and rear to prevent (lessen) any sag in that width. Another alternative you could use is to attach a piece of angle iron front and back. Of course you could hide this with a slim piece of wood. Final solution is to make the top as a torsion box which would then be much sturdier. HTH. :wink:

 

[deserter]

Here's a Web page that will help you work out what to do for the best mate.

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

Hope it helps.
Chris.

 

[cusimar9]

Anything 18mm thick would sag over 1200mm with a 5+ kg weight on it, even ply.

You will definitely need rails, as mailee said at least 2" front and rear. If it were ply you could get away with just a rear rail I think.

 

[Harbo]

Yes I can prove that - 38" span 18mm oak veneered MDF:

Rod

 

[dejaa]

Hi
actually it will sag over that length with just its own weight. Could you not make a triangular filet and locate it at 600mm. That way you'll have support at the front and rear, as apposed to a post at the front only. Also it would allow you to sit at ot without interfering with your knees.
David

 

[Zeddedhed]

Lower the sides by either 18mm or 36mm and then add an extra one or two layers of MDF to the top.
I made some desks for my old construction company offices like this and then put a 10mm x 36mm hardwood strip on the front edge. No sag over 1.5m span

 

[markblue777]

Hi All,
Thanks for the input, I will have a little redesign and get it so i can have a nice 2" bar/torsion box hybrid solution.

Thanks
again
mark

 

[ColeyS1]

Bit off topic but didn't there use to be a piece of hardware you could let into wardrobe doors that allowed you to tension a bow out of the doors (straighten them if they'd become bowed)

 

[DiscoStu]

My work benches are all 2x18mm MDF tops and probably span the same or of distance - not had any problems with them and they have had a lot of weight on them.

 

[Mar_mite]

Bit off topic but didn't there use to be a piece of hardware you could let into wardrobe doors that allowed you to tension a bow out of the doors (straighten them if they'd become bowed)

Your right. It was two long rods with a flat plate screwed in top and bottom, joined with some sort of mechanism in the middle that allowed you to either shorten or lengthen the rods. I made a load of wardrobe doors for a job once. Out of about 20 doors, two went like bananas. These things did sort it, but it was a lot of work letting them in and hiding them.

 

[deserter]

Sounds like a glorified guitar truss rod, I can see how hiding them could be a pain.