Replies

1. 
   BenM | Feb 20, 2004 06:51pm | #1

   MDF is a terrible material for bookshelves since the glue is subject to creep.  That's why the shelves sag after a year or so, even though they didn't when you built it and the load on the shelf has not changed.  Have you tried solid wood?  For a 24 inch span even 3/4 inch pine should work.  You can check out a "sagulator" available somewhere on the net to determine the desirable thickness.  My preference is to use 5/4 wood which gives a nice hefty look to the shelf and is good up to about 36 inches.

1. 
   JMartinsky | Feb 20, 2004 07:00pm | #3

   Sorry that should read "What". In any event, I looked at the sag chart on the web and I think that it is optimistic to say the least. I do this for a living and my work is imortant to me. I don't want these things to sag ever. So that's one vote for solid stock, anyone else?

   John

2. 
   IanC | Feb 20, 2004 07:00pm | #2

   John,  Seems like a piece of 3/4 birch ply with a 3/4" x 1 1/2" wide maple front edge glued on would be plenty strong for a 24" span.  You could add a 1/4" spline across the length for added measure.  I've used them in spans up to 36" with no sagging, full of books. 

1. 
   JMartinsky | Feb 20, 2004 07:02pm | #4

   It is, initially, it is over the course of a few years that they sag. I work in some pretty high end, homes and ANY sag becomes unacceptable. Unfortunately this doesn't even lead to call backs. It stops calls altogether.

   John

1. 
   IanC | Feb 20, 2004 07:20pm | #5

   Well heck, if moneys no object go for the solid stock.  I thought you were on my budget!

1. 
   JMartinsky | Feb 20, 2004 10:57pm | #7

   Well, it's not so much that money is no object, its' just that expectations run high. For me, from a commercial standpoint, the savings in using sheet goods is more than offset ( I think) by all of the labor involved. If I can reduce my labor to a few passes through the jointer, planer & shaper, then I think that I will be ahead of the game. I jsut wasn't sure if there is much of an issue with warpage or checking. For paint grade, I would use soft maple, whech is fairly reasonable around here.

   Thanks For The Reply!

   John

2. 
   BG | Feb 20, 2004 07:40pm | #6

   JMartinsky,

   After I saw your post I checked out my antique library piece in the living room. This piece has 48" (about)x 8" shelves for legal books and a fold out writing desk, with storage underneath.  The shelves are 7/8" thick..and appears to be very straight grained....its about 165 years old, english made.

1. 
   JMartinsky | Feb 20, 2004 11:00pm | #8

   Well, that's good news! Did you happen to get the species of wood? I am guessing oak of some type.

   Thanks Again!

   John

1. 
   BG | Feb 21, 2004 01:12am | #12

   JMartinsky,

   If it were two weeks ago I would confidently tell you the shelves are 7/8" Mahogany...but in the last two weeks Jon Arno has shattered my confidence in being able to distinguish old walnut from old mahogany..sigh. 

   I will say that if your customers are from Southeast CT....they will quickly recognize the solid wood...be grateful..and if it does still warp will call...

2. 
   JBD | Feb 21, 2004 03:15am | #13

   I'm surprised that noone has suggested solid edging on front AND back of ply shelves.  That's what I've always done on wide shelves (30" +) without any problem at all. 

   I've even done 48" shelves in torsion-box construction.  PL Premium Polyurethane construction adhesive glued rips of 1/2" x 1" ribs longways with 1/2" cab ply face skins.  Killer strength, especially when I clamped an intentional crown into the shelf.   PL is the best adhesive ever made for gluing ply.  Stronger than Gorilla glue, and a fraction of the cost.  

   Most of the time I always did 3/4 x 1-1/2" hardwood faces shot on edge of ply - never had a problem.

   Solid wood shelves aren't a good idea due to twist and warp potential, unless the solid is segmented, butcher-block style, say 3 or four pcs to make up the 12" depth.   

   "The furniture designer is an architect." - Maurice DuFrenes (French Art Deco furniture designer, contemporary of Ruhlmann)

   http://www.pbase.com/dr_dichro   http://www.johnblazydesigns.com

3. 
   JMartinsky | Feb 21, 2004 05:18am | #15

   That's an interesting method. Do you wet the plywood before applying the PL?

   John

4. 
   JBD | Feb 21, 2004 06:48am | #16

   In all the years I've used PL (since the late eighties, many, many gallons since), I've never had a joint uncured due to lack of moisture.  The moisture in the ply, and air is plenty - very thorough cure usually.   I use PL for the production efficiency aspect, as I was trying to make a living in cabinetry then, and using a glue that does not require clamp pressure is a real plus - cordless Impulse finsh nailer in one hand, PL in the other, and boom the shelves are done.  PL will expand and bridge gaps well, but won't foam all over badly like Gorilla glue.  PL has higher cohesion than gorilla glue too.   

   "The furniture designer is an architect." - Maurice DuFrenes (French Art Deco furniture designer, contemporary of Ruhlmann)

   http://www.pbase.com/dr_dichro   http://www.johnblazydesigns.com

3. 
   eddiefromaustralia | Feb 20, 2004 11:11pm | #9

   John,

   Try a solid timber front lipping that is about 1.5" x 2", put the 1.5" vertical and the 2" dimension horizontal.

   Run a rebate into the lipping that extends about 1.5" into the stock.

   This will support the front of your shelf and minimise sag.  Profile the front of the lipping to suit.

   I use ply or veneered chipboard/MDF for shelves - approx 16mm with a lipping of this type where a library/bookcase is involved.

   Cheers,

   eddie

4. 
   CharlieP | Feb 20, 2004 11:19pm | #10

   For many years have been using 3/4 inch plywood, with a front edge, as suggested by someone else, with no apparent sag.  But the latest batch of furniture grade 3/4 was actually much closer to 5/8 (far less than 23/32) and only 5 ply, and significantly lighter.  Bottom line, I worry about that kind of plywood much more than with the really heavy 3/4 inch that I have gotten in the past. 

   I have been using plywood "forever" because I was taught that it sagged less than solid wood.  But I recently ran into someone who only used solid oak for shelving, because solid oak sags less than plywood.  I have seen all kinds of conflicting charts, but the stiffness of solid oak makes sense.  I can't believe that pine or some of the other woods would be clost to as stiff. 

   If you use two layers of shelving, the stiffness is double.  But if you use two layers firmly glued together, the stiffness is much more (I don't remember my engineering formulas, but I think it was 8 or 16 times as stiff - third or fourth power).  But those layers have to be glued without creep, which rules out ordinary carpenter's PVA glue.  And poly (Gorilla) pushes the layers apart.  I have heard that urea formaldihyde (plastic resin) would work here, but have never tried it.  If you go down this path, you might be able to drop to two 1/2 inch layers, with the right glue, and get the stiffness you are looking for at a reasonable cost.  

   ________________________
   Charlie Plesums  Austin, Texas
   http://www.plesums.com/wood

1. 
   IanC | Feb 21, 2004 04:29am | #14

   Charles, I  agree with your assessment of new vs. old 3/4" plywood. Same point I'm trying to make in the "why not 3/8th ply" thread.  The industry has pushed the thickness issue to the point that things we used to do with plywood can no longer be done, at least with any integrety. I won't use so-called 1/4" ply for a drawer bottom over say 12" wide.  So now I glue up solid 1/2" poplar and taper the edges to 1/4" for larger drawer bottoms.  A lot of extra work and expense.

   Gluing up two 1/2" pieces for shelving makes good sense but isn't it a shame that we have to when one piece of 3/4 used to do the job.

   OK, I'm through ranting about plywood.  Things ain't gonna change anyway.

5. 
   lynnroy | Feb 20, 2004 11:24pm | #11

   I use 1 inch hardwood edge band and no sags yet. What size books are shelving?

6. 
   mudman | Feb 21, 2004 09:48pm | #17

   Have you tried the "baltic birch" ply? It uses twice as many veneers and all are of birch. Also if you can get away with it laminating with a formica type material makes a tremendous difference in stiffness. You can buy natural wood formica that looks beautiful.

    I have never tried this but you could probably just laminate the bottom and leave the top as is for cosmetic reasons. The lamination resists the surface tension stresses that cause sagging. Mabey some of the old hands could comment on this.

   Mike

7. 
   slem2 | Feb 23, 2004 10:52pm | #18

   I built shelves next to the fireplace which has an antique red oak mantel so I wanted to match the shelves to the mantel. I used 3/4 oak plywood which at the time was running $48 for a 4x8 sheet. The shelves were 16 inches deep by 36 inches wide. I added 1 inch thick by 1 & 3/4 wide by 36 long red oak solid wood to the front of the shelves using glue and brads. The shelves were deep enough to put a false back into some of them where I kept vidio tapes behind a row of books. When I moved to a new home 5 years later I took the shelves down and the fireplace mantel and brought them to the new home[the house I moved from was being torn down so I got to keep anything I wanted when I moved]. The mantel is in my new living room and the shelves are serving as doors to a new workbench I built in my new shop. They are still as straight as they where when I first cut them from a 4x8.    BT