single board or laminated

[GrahamIreland]

which is more stable as a shelf - a single piece of board (larch) x 150mm wide

or multiple rips say 3 x 50mm glued together.

im concerned about movement overtime..

thanks

 

[Argus]

A bit of online research will bring up 'Torsion-Box shelving', which will likely solve your problem regarding strength and resistance to deflection under load.

For example, hardback books are the heaviest load. As a rule of thumb, I seldom exceed a shelf width of 30 inches using 1" thick Oak boards, reinforced with 1" x 2" strips side-on back and front... after that it's a torsion construction.

There is quite a lot of detail on You-tube which explains how to make a torsion-box shelf. Not difficult.

 

[Sgian Dubh]

which is more stable as a shelf - a single piece of board (larch) x 150mm wide

Neither, and a full answer would be relatively complex. But, briefly, if there's going to be a tendency to warp because of changes in moisture content, and you're using a tangentially sawn board, any shrinkage due to moisture loss tends to result in cupping (concavity) towards the bark side of the board. Conversely, moisture gain is most likely to result in cupping (concavity) towards the pith side of a board.

So, if you keep your tangentially sawn board in one piece and make it 150 mm wide you're most likely to end up with a single concavity across the board's width if there is either moisture adsorption or desorption. If you make three pieces out of a wide enough board with each piece 50 mm wide and re-join them with alternating end grain smiles and frowns you're most likely to end up with three alternating concavities and convexities across the glued up board's width if there are changes in the wood's moisture content.

As I said, to get a comprehensive response of causes of warp (not just cross-grain warp) and how to reduce the likelihood of that occurring would really need quite a long illustrated text, something I don't think I can do justice to here.

For your needs though, probably the best thing would be to find a means to hold your shelf flat whether you use a single piece or edge joint a few pieces together to make up the width: this could be through construction, bearers, or screwing the wood down to shelf brackets, and so on. Also, use a piece of wood which is close to the moisture content it's likely to experience in service, e.g., if your shelf is for a habitable building don't use a piece of wood wetter than about 11-12% MC at the time you make and/or install it. Slainte..

 

[Jacob]

At this post I always chip in unhelpfully and pedantically to say that "a torsion box" is just "a box".
The word "torsion" is redundant. There are no boxes which are not "torsion" boxes in the sense intended.
It's a word which has slipped in to the amateur woodwork scene in recent years and originated in J.E Gordon's excellent book "Structures or why things don't fall down" where he describes how biplane wings resist torsion - the bracing cables turn them effectively into a box.
As a rule very few shelves have to resist torsion anyway.

 

[GrahamIreland]

For your needs though, probably the best thing would be to find a means to hold your shelf flat whether you use a single piece or edge joint a few pieces together to make up the width: this could be through construction, bearers, or screwing the wood down to shelf brackets, and so on. Also, use a piece of wood which is close to the moisture content it's likely to experience in service, e.g., if your shelf is for a habitable building don't use a piece of wood wetter than about 11-12% MC at the time you make and/or install it. Slainte..

well ya, I didn't say I would be screwing onto metal angle brackets which I guess should bring more structure.

But I can see what you're saying regards cupping. The rotating of multiple pieces sounds like it brings more rigidness all right.

I can make table tops, and use breadboard ends, just a lot of work for a simple shelf isn't it!

I might stick a piece of oak in instead - it might bend less.

cheers

 

[GrahamIreland]

At this post I always chip in unhelpfully and pedantically to say that "a torsion box" is just "a box".
The word "torsion" is redundant. There are no boxes which are not "torsion" boxes in the sense intended.
It's a word which has slipped in to the amateur woodwork scene in recent years and originated in J.E Gordon's excellent book "Structures or why things don't fall down" where he describes how biplane wings resist torsion - the bracing cables turn them effectively into a box.
As a rule very few shelves have to resist torsion anyway.

so its a box effectively, again a lot of work just for a shelf in my kitchen.

but when isn't it with woodwork!

 

[Sgian Dubh]

well ya, I didn't say I would be screwing onto metal angle brackets which I guess should bring more structure.

I can make table tops, and use breadboard ends, just a lot of work for a simple shelf isn't it!

I might stick a piece of oak in instead - it might bend less.

For one simple shelf I'd just cut your larch to width (150 mm) and screw it to your brackets, assuming the wood is dry now, and also flat. I wouldn't bother joining pieces to make up the 150 mm width.

A piece of oak would be fine too, if you've got it to hand.

In the end, if it's just one simple shelf and what you do doesn't work because of severe cupping or other form of warp, well, you can always knock out another one and just make sure you select better (more stable) material and if necessary to get the required width, join some pieces together. Slainte.

 

[Henniep]

so its a box effectively, again a lot of work just for a shelf in my kitchen.

but when isn't it with woodwork!

A couple of extra mounting brackets, possibly a stiffener along the front edge and a good coat of sealer will reduce distortion and sagging - just a thought

 

[Jones]

A shelf of only 6" width won't cup much unless it's right from the edge of the log so a simple plank will work fine. 1" is ok to span 3' with normal loads ,if it's supported on brackets you can overhang quite a bit either end. To stiffen a plank you can add batten glued and screwed along the edges. Adding a bottom to form a box is mostly decorative and not structual , there would need to be alot of bend before the stress in that skin added strength

 

[TheTiddles]

so its a box effectively, again a lot of work just for a shelf in my kitchen.

but when isn't it with woodwork!

I think Jacob is a good decade or two into not understanding the difference, if you want a light and stiff thing, have a look.