Alcove shelving

[old486whizz]

Heya guys,

Firstly sorry for asking what seems like another repeated subject - I did a forum Search but the questions I had didn't seem to get answered.

TLDR; the alcove dimensions are 140cm wide, 30cm deep. Plan to use 2x25cm metal shelf supports, sides and back, 12mm plywood top, 3.6mm bottom, 25mm wood batons, worried about possible sagging.

Longer explanation:
In an alcove you have 3 sides shored up with the wall, and if the alcove isn't too wide then you don't need to worry about the front sagging too much. This applies to the "floating" kind or whatever.
But, if you have a wide alcove (like me - 140cm), you are left thinking: "if I put a beam across the front - that is just wood that will sag!"... Unless I use a thick wood beam or metal or something.

I have found some 25cm long metal supports that I could put onto the wall - they wouldn't support the full 30cm shelf depth but 85% isn't too bad, and if everything is glued and screwed/nailed then I don't expect much sagging or support issues. Is 2 enough (spaced at about 45cm and 95cm) to help support the shelf?

So my questions are: what sort of thickness of wood should I be looking at for the front support to avoid sag and ensure I'm not under-shpporting the shelf?
No walkthrough really goes into the rules about wood thickness in relation to the gap and the spacing/ frequency of any internal supports.

Thanks.

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old486whizz

 

[foxhole]

Not clear from your post , are you aiming for “floating shelf”?

 

[old486whizz]

Thanks for asking..

Floating looks the best, so that is the initial plan.

--
old486whizz

 

[foxhole]

What type of finish!

 

[Deleted member 174758]

So my questions are: what sort of thickness of wood should I be looking at for the front support to avoid sag and ensure I'm not under-shpporting the shelf?

Feed your data into an on-line calculator called The Sagulator. It is American, so they use terms like "melamine" where we say "MFC" (melamine faced chipboard), but it will work in metric. If you know your sizes you can work out what you need for conventional shelving. I've used it for the best part of 2 decades now and it is pretty reliable. As a general rule, most non-floating shelves use 18mm or sometimes 22mm material, probably because they are most widely available) and they leave you needing supports at somewhere in the region of 400 to 500mm apart to avoid sagging (and hit studs in stud walls)

No walkthrough really goes into the rules about wood thickness in relation to the gap and the spacing/ frequency of any internal supports.

I think you'll find that calculator above is a great help, however floating shelves are a whole different barrel of fish...

Because you are aiming for a thickness of 35 to 50mm floating shelves get extremely heavy if made from the solid, so it is mormal to make them up with a hollow core and thinner skins in order to reduce the load that the fixings carry.

 

[Tigercubrider]

Depends what you intend to put on it.
Books weigh a ton, decorative objects spaced out

a box section is very strong

a hollow box is easy to make if you get the wood cut correctly, and add blocks inside to accept floating shelf parts
There are bloody expensive floating brackets that simply screw to the wall and to the back of the shelf and clip together.

 

[Deleted member 174758]

So, if you are going for floating, how good is your woodworking? In other words are you going to "roll your own"?

 

[thomp1983]

Use 25mm steel box section to make the frame of your shelf, bolt it to the wall on the 3 sides then finish with wood, the box section shouldn't sag unless you massively overload it.

Can't imagine any local welder would charge much for what's a simple job