Are there ways I can stop a long bookshelf from sagging?

[Doris]

Hi everyone,

We're about to build some bookcases into the alcoves of our dining room and these will be stand alone cases, rather than built onto the wall.

Here's a sketch up I did of the wall and cases I would like. (The background is painted green as the wall but will be a plywood back)

One bookcase will have shelves roughly 110cm long and the other 100cm. We were going to make the whole thing from plywood, including the shelves which would be two sheets glued and then with a face frame in front to add strength.

I know that making shelves out of plywood this long is a bad idea as they would sag. But is there a way we could make the shelves this length stronger without having to resort to using dividers?

Thanks everyone

 

[marcros]

you could make them as a torsion box.

when you say 2 sheets of ply, are we talking 12 or 18mm here?

you could possibly fir a batten underneath so that it wasn't seen from the front, and so that it is trying to bend against its longest plane (ie 2x1, attached to the shelf by the 1 side)

 

[RogerP]

Fix the rear edge of the shelves to the plywood backing?

 

[Phil Pascoe]

Off tack, but make sure you space them off the wall, or everything will more than likely end up damp.

 

[ColeyS1]

I'd use tulip wood instead- much better for this type of job.

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[gmgmgm]

I trust you've found and used the "sagulator" website to check the expected deviation?
Doubled-up ply is pretty strong, but half of the grain will be going the "wrong" way so not really adding the strength you need. Using hardwood at the front will add strength.
You could also sandwich some metal in the horizontals to add strength.

There will be some other tips if you search the forum, but these are the ones which spring to mind.

 

[WoodMangler]

I addressed a similar problem on a long unsupported desk-top by rebating 20mm angle-iron into the front edge. and facing over it with a bit of hardwood moulding.

 

[custard]

30mm thick shelves (torsion box, two sheets of 12mm with 6mm spacers. 30x40mm tulipwood lippings front and back. Widest span 950mm, zero visible sag.

 

[cambournepete]

Off tack, but make sure you space them off the wall, or everything will more than likely end up damp.

Why?
Particularly if it's an internal wall...

 

[Jacob]

Ply and mdf unsuitable for shelves. Innately bendy. Solid wood much better. Redwood is fine.
If too thin you could add a batten to the front edge (make it into a decorative half round moulding?) and support the back edge.

 

[Phil Pascoe]

Off tack, but make sure you space them off the wall, or everything will more than likely end up damp.

Why?
Particularly if it's an internal wall...

Because every time I've put bookshelves that size against a wall for any length of time, It's ended up slightly damp behind them. More likely on an external wall, certainly, but paper is hygroscopic anyway so just to keep your books smelling sweet and your decor clean, it doesn't hurt to leave an inch of airspace.

 

[John Brown]

Buy a Kindle.

 

[Phil Pascoe]

Can you get Holtzapfel's treatise on ornamental turning on one? Or a 1961 Larousse Gastronomique? Thought not. :lol:

 

[John Brown]

Can you get Holtzapfel's treatise on ornamental turning on one? Or a 1961 Larousse Gastronomique? Thought not. :lol:

No, but it is a solution for sagging bookshelves.

 

[Bigdanny]

When I was in the UK I had a couple of alcoves either side of a fire place. I sure I used 6mm ply above and below with roofing battens fixed against each wall and across the front. I filled in the front with plaster of paris and then painted. I think they were about 80 or 90 cms wide. I may have screwed a batten in the centre as well.They never cracked or bent and I had some quite hefty books on there.
They looked good and chunky with no visible fixings.
HTH
Danny

 

[mailee]

I would also go with the torsion box solution. I built some wide wardrobes with a shelf above and used this method and I could hang off it it was so strong. (That was 12mm MDF) :wink:

 

[doctor Bob]

I would also go with the torsion box solution. I built some wide wardrobes with a shelf above and used this method and I could hang off it it was so strong. (That was 12mm MDF) :wink:

Alan is a 22 stone bodybuilder by the way................

 

[AndyT]

Can you get Holtzapfel's treatise on ornamental turning on one? Or a 1961 Larousse Gastronomique? Thought not. :lol:

For Holtzapffel volumes 1 to 4 read down this page

http://www.woodworkinghistory.com/manuals_1900-before.htm

Vols 1 and 3 are also available here

http://www.evenfallstudios.com/woodworks_library/woodworks_library.html#Turning

- all in PDF format, readable on any Kindle, tablet, laptop, iPad etc. and free.

You might have to settle for a newer Larousse, I admit, but that's not woodworking!

 

[Ed209]

I personally think it would look ok with dividers, they would give it a bit of interest and a designed for purpose engineered look.
Also make your books, LPs if applicable more manageable.
Not really solving your problem I know.
You could make the shelfs like the ones you get from IKEA etc. with the concealed support brackets



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[Jacob]

The only problem is in using the wrong materials.
If you use mdf or ply you have to go to a lot of trouble with "torsion boxes" or whatever (NB there's nothing "torsion" about them they are just "boxes" as beams).
If you use "wood" (grows on trees) and if it's thick enough it'll be fine, and thinner and cheaper than a so-called torsion box.
You could make shelves from recycled cardboard if you put your mind to it, but why bother?