Replies

1. 
   Samson | Jan 26, 2006 06:01pm | #1

   1/2" plywood is only nominally 1/2" - that is it's likely 1/32" (or more) less than 1/2".  I mention this only on the chance that you are cutting dadoes or something and where counting on a true full 1" thick shelf

   Titebond should work.  Don't use too much glue as it makes it difficult to keep the edges aligned when clamping the boards during glue-up (they slide around on each other and the glue prevents smooth and even contact across the wide expansive of gluing area - think of it as puddles that can't escape) and makes a bigger mess of drips.  Sometimes, when I laminate sheets or planks like this, I leave them oversized for glue-up and then trim the edges to the exact dimensions after with a tablesaw or router.  This makes the exact matching of the edges and cleanliness of the edges less of an issue during glue-up.

   
   

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   Edited 1/26/2006 10:04 am ET by Samson

1. 
   Marion | Jan 26, 2006 06:09pm | #2

   wow! thanks for fast reply. Yes, I know that I'm not going to end up with a true one inch, but thanks for the comment. I am going to glue oversized and then cut to finished size. I will glue piece of wood to front to get the "real" wood look.

1. 
   Samson | Jan 26, 2006 06:17pm | #3

   Re-read your initial post: if your question was input on the type of glue, I have more that might be useful.

   Titebond II is not the best choice.  It only has about 5 minutes of open working time before it starts to set up, which can lead to some frantic clamping.  It's also optimized for exterior use.

   Titebond III would be a better choice, as it is interior/exterior and has a 10 minute open time.

   My personal favorite however is LeeValley's 2002 Cabinetmakers Glue:

   http://www.leevalley.com/wood/page.aspx?c=2&p=45104&cat=1,110,42965&ap=1

   It has a 20 minute time, is very strong, and has good fill capabilities (high solids content).

   Edited 1/26/2006 10:18 am ET by Samson

1. 
   Marion | Jan 26, 2006 06:51pm | #4

   Thanks for info on glue. I will get some lee valley glue and try it out.

2. 
   loucarabasi | Feb 04, 2006 02:19pm | #15

   Marion, You may know this allready, Try glueing the pieces with both crowns up, which will allow for some sag in the future. Then again when you want to sag it wont.

   -Lou

2. 
   Jfrostjr | Jan 27, 2006 05:12pm | #5

   You don't mention how long you intend to span with the shelves.

   A few years ago I built a wall unit and used 3/4" ply for 36" shelves. In a year they began to sag. I replaced them with 4 quarter solid stock and am much happier and more secure. The price wasn't too bad.

   Jerry

1. 
   Marion | Jan 27, 2006 05:20pm | #6

   How much weight did you have on them?

1. 
   Jfrostjr | Jan 28, 2006 05:47pm | #7

   Sorry to be slow in responding. I hit the e-mail every morning and rarely at other times.The shelves carried the usual assorment of ordinary books, some 3 ring binders, paper backs or instruction manuals. Nothing out of the ordinary. I think there is some imperceptible slip between the plys of the plywood which are not as tightly bound as actual wood fibres. Another advantage of solid wood is the fact that you don't have the problem of facing the raw edges.Good luck,Jerry.

1. 
   Glaucon | Jan 30, 2006 05:36pm | #8

   As the owner of many books, and the maker of more than a few bookshelves, let me make a few observations:

   1. Solid wood (hard or soft) is less likely to sag than plywood of the same thickness.

   2. The longest run you should contemplate for 3/4" stock is 30".

   3. If you plan to run 36", use solid 1" stock (buy 5/4 and mill to 4/4).

   4. I have a book or article somewhere whch actually tested weights, spans and materials and plotted the sag by thickness.  It's more than a few years old, but I've pretty much commited the above to memory and found it to be accurate.

   5. If you use solid wood, you have the option of using dados and sliding dovetails for the joinery. The latter is particularly good for bookshelves.

    Glaucon

   If you don't think too good, then don't think too much...

3. 
   WesHighfill | Feb 02, 2006 02:30pm | #9

   Another option is to stiffen the 3/4" ply shelving with thicker (or taller, depending on how you look at it) solid wood edging.  This helps stiffen the shelf, especially if you do it front and back, which might be necessary if you're spanning a long distance.  I tested this recently by taking a 3/4" plywood shelf that was about 60" long and biscuited and glued a solid wood edging on the front and the back (2" tall).  I supported the shelf at its ends so that it was a couple inches over the top of my table saw.  Then I mounted a dial indicator with a magnetic base and set it up to measure the deflection in the shelf.  I started by stacking full gallon cans of paint right in the middle of the shelf.  With 9 gallons of paint, it deflected somewhere around 1/32 - 1/16".  So to really put it to the test, I climbed up there (without the paint).  I weigh about 190 lbs., and it deflected 1/4".   That satisfied me that the shelf would hold some books. 

    

   Wes

1. 
   Marion | Feb 02, 2006 07:10pm | #10

   I like the image of you standing on shelf on top of your tablesaw. ;)
   I have come up with two ideas for shelves. One is to make torsion boxes and use them. The other is to add square tubing inside glued up 1/2" ply sandwich. I am making a built-in wall unit and want the shelves and uprights to be just about 1". I don't think adding wooden strip that is only 1" will add that much to stiffness.

1. 
   WesHighfill | Feb 02, 2006 11:08pm | #12

   How are you keeping the steel square tubing in place in the plywood sandwich?  Glue?  That's a fantastic idea.  How wide of a shelf are you making and how many steel tubes are you putting in it?  Have you tried aluminum square tubes?  I was thinking of weight savings.  How are you attaching the shelf at the ends, a great big dado? 

   I agree that a 1" wide edging won't do as much...if I remember correctly, beam strength is proportional to the square of beam thickness, or something like that. 

   As far as standing on a shelf on top of my tablesaw, I'm just glad my wife wasn't around at the time.  She already thinks I'm nuts and that would've proven it to her. 

1. 
   Marion | Feb 04, 2006 07:26pm | #16

   hello
   my plan is to rip dado in plywood 4 inches in from front and back. This will be what the 1/2 square tube will set in. The I will attach the bottom sheet of plywood to front back and sides with pocket screws and titebond. Then I will use epoxy to glue and fill spaces with tube inside. The top will get nailed on and clamped until dry. I will do a mockup next week on another shelf project to see if it works. I only need two moveable shelves for built-in. The other two shelves I will screw in through 1/2" back.

4. 
   Troy | Feb 02, 2006 08:58pm | #11

   Sorry to jump in, have you tried some of the lumber suppy places that cater to the cabinet industries, I have purchased some baltic birch that is just over an inch thick I think it was 30mm. Heavy but less work than glueing up to 1/2 sheets.

   Troy

1. 
   Marion | Feb 02, 2006 11:11pm | #13

   Troy,
   What I am looking for is to span 40 inches. I am still in the planning stage of cabinet. I think for the overall look of a 12' unit, 3/4 looks to thin, 3/4 edged with 1 and 1/2 wood looks a little thicker than I want. The people came to me with a picture of bookcase wall from Better Homes & Garden and I am modifying it to turn it into TV/bookcase unit.

1. 
   Troy | Feb 07, 2006 02:22am | #17

   On shelves I have also added a 1x2 piece to the front of the shelf and that has helped stiffen it quite a bit as well as giving the shelf some added mass. I also put a 1/4 inch rabbet in the 1x2 to give some additional glue area. If you put a 1x2 in the front and back that will give you a very stiff self. Good luckTroy

5. 
   dchyatt | Feb 03, 2006 02:40am | #14

   Have you considered putting 1/2" backs in your cabinets and then adding a row of shelf supports in the center of the back?