Sagging MDF shelf

[RossT]

Hi,

I’m looking for a bit of advice please - I need to span a 1300mm gap to create a shelf, and I was trying to use MDF. I’ve already supported it across the full length of 3 sides, and I’ve layered 2 sheets of 12mm MDF with glue and screws to try to make it more rigid, but it is still visibly bowed across the front edge, even before I put weight on it.

Can anyone suggest a wood or technique that would span the gap, without bowing and without the need for a bar supporting the front edge please?

 

[custard]

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

This will help you find a solution.

 

[ColeyS1]

Tulip wood !

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[dzj]

Perhaps some hidden floating shelf brackets might work.

 

[Beau]

I got caught out using MDF for some shelves. The bottom line is its not a good material for something that needs directional strength like a shelf. Can you put a deep solid wood capping on the front of the
shelves? Say 50mmX50mm

 

[Fergal]

A length of angle iron or box section steel screwed to the shelf from underneath?

 

[ColeyS1]

A length of angle iron or box section steel screwed to the shelf from underneath?

I did something similar for my cupboard.

Screwed a piece of oak batten underneath to try and help stop it bowing.
You would never think it would bow as much but it does. I've found even 30mm mdf will bow under its own weight. You really can't beat tulip wood, or a solid wood edging.

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[LancsRick]

Why the specific love for tulip wood for this purpose?

 

[ColeyS1]

Why the specific love for tulip wood for this purpose?

I was just assuming it was going to be painted. It takes paint well is more stable than softwood and doesn't cost as much as beech for example. It's probably the cheapest paintable timber I can think of that's resists sagging,much better than sheet material.

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[custard]

Whopping great solid wood lippings, front and back. I think from memory the lippings were Tulipwood (Poplar), as Coley said it's cheap, stiff, and nothing takes paint better.

 

[Jacob]

Normal redwood is best for shelves. Cheap, easy to work, light, and stiff. I've got some bookshelves 100+ years old with redwood shelves sitting on 1/2" dowel pegs. No prob.
MDF is hardly better than cardboard!

 

[Adam9453]

As others have said, solid timber lipping to the face edge or rebate a piece of steel angle into it so it’s concealed. If solid timber lipping then use a piece of timber slightly over thickness, glue it on and plane or sand it flush with the surface of the mdf

 

[RossT]

Thanks everyone. I think I’ll try a combination of box steel recessed into the surface and a wooden edge trim. Good tips!

 

[skeetstar]

Folks, I am looking at making a mobile reception desk for a place near me. Customer wants it 6ft side to side, I need to agree the front to back dimension with her yet, but I was contemplating using MDF for the top. The top will have to bear the weight of a PC and elbows of receptionists. Carcass will be softwood and ply.

Reading the above, it looks like MDF is a non starter given the size I need to go to. The sides will be straight edges, the front and back edges will be gently curved. Any suggestion as to what I could use for the top? Customer wants the whole thing including the top working surface painted white.

Good job I read this thread before I started to,spend money.

 

[thick_mike]

Does the top need to span the whole 6ft?

My preference would be to use birch ply and some sort of torsion box arrangement if the design allows.

 

[Beau]

Folks, I am looking at making a mobile reception desk for a place near me. Customer wants it 6ft side to side, I need to agree the front to back dimension with her yet, but I was contemplating using MDF for the top. The top will have to bear the weight of a PC and elbows of receptionists. Carcass will be softwood and ply.

Reading the above, it looks like MDF is a non starter given the size I need to go to. The sides will be straight edges, the front and back edges will be gently curved. Any suggestion as to what I could use for the top? Customer wants the whole thing including the top working surface painted white.

Good job I read this thread before I started to,spend money.

Structurally blockboard with a capping would be good but dont know how good the facings are of it having not used any in years.

 

[HOJ]

I made this reception desk from Oak venered MDF, quite a few years ago.

I used 2 steel sections to support the top, spanning between the the 2 sides, one towards the front edge, and another set towards the back, its still going strong.

Sorry, pictures not very good.

 

[Sideways]

Just another voice saying MDF is useless for shelves. It is just sawdust and resin - there's nothing in the structure to resist sagging.
Maple is excellent for bookshelves - very stiff.
My birch ply workbench top (admittedly thick) lasted 30 years without sagging. I'd look at a birch ply torsion box too if I had a 6' span to deal with.

 

[Just4Fun]

Structurally blockboard with a capping would be good but dont know how good the facings are of it having not used any in years.

Is blockboard still made? I haven't seen any for 20 or 30 years.

 

[Beau]

Structurally blockboard with a capping would be good but dont know how good the facings are of it having not used any in years.

Is blockboard still made? I haven't seen any for 20 or 30 years.

I had to google it myself but yes there is a seller on Ebay.