Replies

1. 
   JohnWW | Jan 13, 2006 06:05pm | #1

   Solid wood isn't all that much stiffer than a good grade of plywood, and a piece that's 3/4 inch square wouldn't add enough reinforcement to matter. 

   If you wanted to add some significant strength to the shelf, make the edging 2 inches wide and attach it with the wide face vertical, it would be about 9 times stiffer.  For maximum strength put the vertical trim on both the front and back edges of the shelf.

   A bit of basic engineering: stiffness is basically a function of thickness and the stiffness to thickness relationship is a square function: double the thickness and the piece will be four times stiffer, triple the thickness and the piece will now be nine times stiffer.

   Hope this helps.

   John W.

1. 
   adirhu | Jan 14, 2006 02:24am | #3

   Hi John:

   Thanks for the information.  I'm disappointed the hardwood isn't really any stiffer than the plywood, but of course it makes sense.  I did reinforce shelves like you suggest on a library I just built for my synagogue (using 1 1/2 inch thickness in the front and creating a lip that fit under and reinforced the 3/4 inch maple plywood shelf).  The problem is that when the shelves are spaced close together, i.e., when there's not much clearance for the books, that extra lip on the bottom of the shelf can be a pain.  But I guess that's just the reality to be dealt with.  What I can do now with your information is treat these shelves as if they're made only from plywood and plug that info into the "sagulator" and see how much weight they can bear.

2. 
   arkriver | Jan 13, 2006 11:40pm | #2

   Woodworkers Supply and maybe others , sell a metal channel that is tapped over the edge of a shelf to stiffen it. I have use then of a the back of a bookshelf shelf and they are essential not visible assuming you have o lot of stuff on the shelf. Also put one on the front of a pantry shelf where the wife puts canned goods. Neither shelf is sagging visilbly after more than a year. This might be something to consider.

1. 
   adirhu | Jan 14, 2006 02:27am | #4

   Thanks.  That's good information about the shelf stiffener.  I'll check into it and see if they can give any specifics on what extra strength it might add.

2. 
   adirhu | Jan 18, 2006 07:47am | #8

   I've checked online with Woodworkers to find the metal channel you write about.  I couldn't find it.  Do you have a more specific name, or company, or part number?

   Thanks.

1. 
   arkriver | Jan 18, 2006 08:46pm | #9

   I checked in the logical places in my Woodworkers Supply catalog and find then either. Maybe they quit carrying then. I got mine about 2 yrs ago. You might give them a buzz. I'll look some more. Sorry

3. 
   dchyatt | Jan 14, 2006 03:01am | #5

   When I am concerned about wide shelves sagging I add a lip as JohnWW suggests. I also add a row of holes for shelf pins at the back of the cabinet in the center.

1. 
   adirhu | Jan 14, 2006 03:35am | #6

   That's an interesting idea, adding the row of holes in the back.  However, I typically use 1/4" plywood in the back, into which I certainly couldn't drill holes.  I assume you must be working with thicker material.  Thanks for the advice.

1. 
   dchyatt | Jan 14, 2006 07:13pm | #7

   Yes, to add shelf holes in the back I would use at least 1/2 inch material.