I need to make some plywood bookshelves, 11″ deep by 78″ wide. The client wants only one dividing space in the middle of the unit, all shelves adjustable.
I’m sure a fully loaded 36″X11″ shelf will sag visibly.
Can I solve the problem with a 1 1/2″ solid nose on the shelf? Would I need to go a full 2″?
Thanks
Jon
Replies
If the unit has a back that can brace the adjustable shelves as well as the sides you'll probably be OK. But of course it depends on what "fully loaded" means. If he wants to put his encyclopedia on it, I would make each shelf a torsion box of doubled 3/4" ply with 1/2" spacers inside and a 2" face frame. It's not that much more cost, and it makes much better looking shelves. You can even make invisible supports when you have a torsion box construction. And you can load just about anything on them without sag.
DR
OK what you posted.. BUT a thick shelf..I would get some 1/4 X 1/4 cold rolled steel 'L" and rabate into the bottom center of the shelf so it can't be seen..MUCH stronger and CHEAPER!
http://www.woodbin.com/calcs/sagulator.htm
Thanks, I did check that, but it only gives figures for fir ply, not hardwood, and does not address the change you might get by adding wide nosing to the shelves.
Got several 34"X 10-1/2" Maple shelves with 2" nosing fully loaded with books (FWW & FHB) and I see no deflection. Rabbeted the nosing 1/4", screwed and plugged'em.
You can also put nosing on the back to increase strength.
I have 48" plywood shelves with 1 1/2" nosing added. i also added 1/4" by 1 1/2" strips to the back and as far as I can see no sag.
you can try adding 3-4 columns of shelf ping holes in the back of the unit and add supports there as well - that may help as well
Do what many professionals would do. Make up a prototype shelf of the desired width and depth. Put the ends on a brick to raise up the shelf. Then load the shelf with whatever it will contain. Measure the sag. If it sags, then nail on a 1 1/2" solid wood board as a front edge and another as a back edge. Measure the sag.
Remember, 36" of novels weighs much less than 36" of encyclopedias or other tall books. In other words, overbuild to be sure you don't get call backs.
Continue exploring options and modifying your prototype until you find one that meets your requirements.
That's a great idea, I'll try it. According to the sagulator, you will get 50% more sag over time than you did when first loading the shelf. Does that fit with your experience?
Judging from the other shelves in the house, this guy likes big, heavy books, and lots of them. He is also strongly in favor of adjustable shelves.
I just finished a set of built in cabinets for a den and was worried about the same question you posed. I used a table from Built In Furniture by Jim Tolpin (Tauton Press), page 120 that shows for 3/4" thick plywood shelving 8" deep, a 36" run will have a maximum deflection of 3/32" with a loading of 35lbs per lin. ft. This seems to show that you will be alright without any additional support but anything like a front or back ledger will only give added assurance. I used a 1 1/2" front bullnose and have had no problems in 5 months fully loaded with books.
Hope this helps.
Ed
Just my 2 cents:
For the shelf that you describe, I would use 1" plywood with your choice of edging. 1 1/2" of hardwood should be more than adequate. you didn't mention species, so I am assuming paint grade maple. Make the prototype and see what you get, but glue and nail the edging on. If that proves unsatisfactory, glue and nail two layers of 3/4" plywood together and face as described. Beyond that, you are into steel or aluminum.
Good Luck!
John
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