Making a bookcase out of 18mm plywood

[UrbanSpaceman]

Hi all,

We have some unused space at the top of the stairs here and I was thinking about making a bookcase to fill the space. It would be 130cm wide and 20cm deep, and extend from floor to ceiling. I would fix it to the plasterboard wall so it would not need to be a free standing one.

Does the font of knowledge on this forum think that 18mm hardwood ply would bow over that distance; will it need bracing? I wasn't planning to put a back on it, but I could use some thin ply (4mm?) if it was desirable to do so. Only planning to put books on it, but 130cm's worth of book would probably weigh a fair amount.

Ready for advice on this, I'm only a beginner!

Mark

 

[marcros]

This may help.

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

Could you put a central upright in it, so the span was only 0.65m I havent ran your numbers through it. A back would certainly help with rigidity.

 

[UrbanSpaceman]

Thanks, I used that and with a load of 30lb (the default, and I guess about right for books) is says a sag of 0.0cm

Maybe I could use an 2x1 as a batten against the wall and lay the plywood on that.

 

[Benchwayze]

Hang the case on French cleats.

I'd use 25 mm stuff myself. It wouldn't cost a lot more, and it won't be so susceptible to sag.
With ply, some moulding work on the edges would hide the laminations to an extent. (Centre-bead looks nice on bookshelves.)
You might find solid PAR pine would be cheaper in that thickness. Looks better and paints well too, if you don't fancy the 'pine look'.

HTH

 

[Baldhead]

Benchwayze what is centre bead?

Baldhead

 

[Benchwayze]

Benchwayze what is centre bead?

Baldhead

I can't draw on the PC, so :

A raised bead and double-quirk along the centre of the edge,
You can use a suitable staff-bead cutter, to produce it,

Or, similar to the cutter I use,

http://www.tooled-up.com/product/trend- ... rce=affwin

You might have another name for the resulting moulding.
HTH

 

[Sgian Dubh]

Hi all,

Does the font of knowledge on this forum think that 18mm hardwood ply would bow over that distance; will it need bracing? Mark

Your bookshelves will definitely bow if supported only at each end. Typically, a bookshelf carries 25 lb per linear foot, or about 11 kg per linear 300 mm. Large format books weigh more. In any case, you'll need some sort of intermediate bracing or additional support to reduce (not prevent) sag caused by creep deformation (relating to flexure formulae and the like, including duration of load, in pure bending [beam theory]). Over the length you've described you should allow for a load of about 108 lbs or 48 kg per shelf.

As others have suggested, and assuming the shelves will definitely carry books, rather than a few lightweight ornaments, incorporate bracing of some sort to prevent visible sagging. A sag of less than 3 mm over a 900 mm length is readily visible to the eye. Slainte.

 

[UrbanSpaceman]

Wow, good answer!

Thanks for that. I'll brace them then.

 

[nanscombe]

If you wanted to brace the shelves, but think that wood may be too thick, how about using a piece of aluminium / steel angle underneath the back edge of the shelf.

Being at the back it should give some support and disappear behind the books.

 

[John15]

Hi Mark,
This link will give you an idea of what sag to expect:
http://www.woodbin.com/calcs/sagulator.htm
Cheers,
John

 

[UrbanSpaceman]

Hi Mark,
This link will give you an idea of what sag to expect:
http://www.woodbin.com/calcs/sagulator.htm
Cheers,
John

Ah, the sagulator. Thanks, this was my first reply to the question!