Replies

1. 
   BArnold | Sep 16, 2004 06:06pm | #1

   Mike,

   Here's a link to an article that should answer any question you have about shelf loading and construction:  http://www.woodbin.com/ref/furniture/shelves.htm

   Personally, I added shelves to an alcove in our house that is an entertainment equipment area.  The shelves are about 48" wide.  In my case, I had three walls to which I attached cleats.  I used one thickness of oak plywood and applied a 1 1/2" x 3/4" strip of oak to the front edge for support.

   Bill Arnold - Custom Woodcrafting

   Food for Thought: The Ark was built by amateurs; the Titanic by professionals.

   ---

2. 
   jackplane | Sep 16, 2004 06:18pm | #2

   The strength of a bookshelf comes more from the the depth, or thickness from a front or front and back nosing, not so much from the material that spans the shelf.

     Doubling the ply seems a waste of resources. I'd glue up the solid wood nosing only. It acts as a floor joist, and the deeper it is, the more strength you have.

1. 
   HowardAcheson | Sep 16, 2004 11:02pm | #3

   In the shop I was involved with, we would always prototype a shelf to answer a question like this. It only takes a few minutes.

   First, get a stack of the books you want to put on the shelf.

   Cut a board the depth and length you plan and put the ends on something like a 4x4 to raise up the board. Then put the books on the shelf and measure the deflection. If it deflects, add a front nosing of your choice and fasten it with nails or screws. Test again.

   You can try a number of scenerios in an hour or so and have an answer you can count on.Howie.........

1. 
   Jimma | Sep 17, 2004 12:20am | #4

   Ditto on Howie's response, but you also need to expect some deflection over time if you have the shelves full and loaded with heavy volumes. The nose is the key if the shelves have three sides supported. Make the nose as beefy as your esthetics will permit and use good hardwood. An alternative is to place intermediate vertical supports above one another. If you do it right they will look about like the spine of a book. I usually build shelves above a plinth or base and use supports set back from the front edge so they appear to be books.

1. 
   Julie1 | Sep 17, 2004 02:53am | #5

   Making the supports look like books is a very clever idea. Too bad we didn't think of that when we made our book shelf.

3. 
   mudman | Sep 17, 2004 07:35pm | #6

   Thanks everyone,

   How do you "reply to all"? I see some of yall can do it. I was planning on mocking it up actually to see, but only if yall thought it had a chance. I've put 2" nosing on the front and back of 36" wide 20" deep 3/4 ply shelves and they deflected a little under a heavy book load. This will be in a church and I really want it to be perfect.

   I read in the archives where someone mentioned creep as a problem when laminating ply with wood glue. He recomended polyurathane (PL brand in a caulk tube). I really dont like using that stuff on wood to wood applications. What do yall use?

   Thanks again,

   Mike

   please excuse my spelling.
1. 
   Julie1 | Sep 17, 2004 08:06pm | #7

   To reply to ALL, its up at the top part of the message that you're composing under your name. Click the down arrow.

   :)You can't fix something if you haven't broken it yet.

2. 
   drhamel | Sep 18, 2004 03:37am | #8

   You also have to be in 'Advanced View'.  That's located at the bottom of the screen when you get to the end of a thread.Formerly just 'Don' but not the 'Glassmaster Don' or the lower-case 'don'.

1. 
   mudman | Sep 18, 2004 10:28am | #9

   Cool, I did it. Now back to the shop to glue up those shelves.

   Mikeplease excuse my spelling.

4. 
   beck4000 | Sep 18, 2004 08:48pm | #10

   Everything you thought you already knew about shelving before they started to sag.

   Whether it is shelving for your own shop or for your clients, do you really know what material will hold how much weight over the long run? We all have sagging storage shelves in our shops, but wouldn’t dare put them into a customer’s kitchen—maybe in the garage? The reality is that there are a lot of variables and complications in deciding how to build shelves.

   We know that shelves in a highly humid environment must be solid wood, or plywood, but not MDF or particleboard because high humidity over time will change all the laws of gravity with certain materials. So particleboard is ruled out in the boathouse and the musty basement.

   No one wants a shelf to break, but what is our tolerance for deflections? A highly visible finished piece of furniture should not have noticeable sag, but a utilitarian closet shelf could dip a bit without a complaint.

   What we are talking about here is the balance between looks and costs. We could make everything bulky and super supported, or we could go for both visual streamlining and cost reduction. For this article I had to look beyond my own rules of thumb developed over years of propping up sagging shelves. I finally located two understandable references for shelving span tables (the engineering formulas are in the back of one of the documents if you want that kind of detail). Of course, they come from two competing associations and force us to do a little bit of comparing apples to oranges. A quick look at the table gives plywood an amazing advantage over the other two materials. It has an advantage, but not that much.

   The difference is essentially in how much deflection is considered to be acceptable for a shelf. The particleboard and MDF people say that slightly more than 1/8” deflection in a 36” span is the limit (1/240), what they call “visibly noticeable.” The plywood people base their calculations on 3/16” deflection in a 36” span (1/180). Actually they are 25 per cent apart. This variation in recommendations is probably due to the tendency to use particleboard and MDF for more finished shelving and plywood for more utilitarian shelving where a slight visual deflection will be tolerated. If you are using plywood and want to follow minimum visual deflections, although I have not done the precise mathematics, a safe bet would be to reduce the plywood spans in this table by about 25 per cent. As expected, plywood still spans farther than the other two, but costs more.

   Here are some very practical things that were included in the particleboard and MDF specifications that are generally true for plywood as well:

   -- For shelves 12 inches or less in depth with continuous support along the back edge of the shelf, the allowable span can be doubled.

   -- A maximum overhang beyond bracket or support not to exceed 6 inches may be added to these spans.

   **Originally published as an article by Jon Eakes in Home Builder Magazine, the magazine of the Canadian Home Builder's Association.

   Hope this helps you! From Jon Eakes!

   If nothing sticks to Teflon,how does Teflon Stick to metal. Huh

5. 
   Midnight | Sep 19, 2004 12:15am | #11

   I was thinking about laminating two 3/4 oak ply pieces together then adding 3/4 x 2 inch nosing in the front and back to stiffen it up. What do yall think? Better yet does anyone have experience?

   Wayyyyyy overkill Mike... there's a far easier, and cost effective way... Firstly... 3/4" ply on it's own will work... but even that's a tad overkill, personally I'd use 1/2" for the shelf. The key to the thing is the bracing. If you screw the rear of the shelf to the back, the back will impart a huge amount of support. To support the front of the shelf, I'd use a piece between 1 1/2" - 2" deep, rebated to let the shelf sit into it, and cut tenons into the ends of it to fit into the shelf dado's. I personally don't go for adjustable pitch shelving, instead, I change the pitch between each shelf to allow for varying book sizes. Provided the fit between each shelf and its dado is good and tight, braced as above, each shelf shouldn't deflect more than 1/4" with a load in excess of 400 lbs on it. I've done pull ups on a shelf damn near the same length..it didn't move at all....

   Mike Wallace

   Stay safe....Have fun

1. 
   mudman | Sep 19, 2004 09:47pm | #12

   Thanks for the advise. Unfortunately this piece is not for me. The customer requires adjustable shelving. I know for certain that 3/4 ply will sag and probably fail over this span (if not anchored to the back). I have built shelves with 1 1/2" nosing for 36" spans and it sagged more than I liked. So I have serious reservations about a 48" span. I am hoping that adding 3/4 x 2" nosing to the front and back will be enough. Ill mock it up in the shop today and let yall know.

   Thanks,

   Mikeplease excuse my spelling.

1. 
   TKanzler | Sep 20, 2004 04:39pm | #13

   May I suggest you use a length of angle iron, buried either inside or behind the nosing.  For a 50 lb/ft book load and 1/16 in deflection at the center of the 4 ft span, a 2 x 2 x 1/8 angle section (I=.190, S=.131) would work.  Max bending stress would be about 9.2 ksi, which gives about a 4:1 factor of safety using the lowest grade of structural steel (after which, there may be a permanent set).

   The above doesn't account for the stiffnes of the shelf itself, or the reduction in bending load due to the shelf being supported at the rear.  It's pretty conservative.

   The angle has to be well fastened to the shelf near the ends (only one or two needed near the center, just to keep it from moving), or better yet, dado the shelf so the inside surface of the angle sits flush with the bottom.  That way, the shelf supports in the cabinet can take the load from the angle directly, without having to allow for the thickness of the angle when locating the shelf supports, and only a few fasteners would be needed.  Structurally, it would be no different than mouting the angle on (in?) the cabinet, and setting the shelf onto it.

   Edit: I should mention that the angle mentioned above weighs 1.65 lb/ft, so you're only adding about 6 1/2 lb to the shelf, but you may be able to use less wood and come out ahead.

   Be seeing you...

   Edited 9/20/2004 9:41 am ET by Tom Kanzler

6. 
   GHR | Sep 21, 2004 01:29am | #14

   My wife has 5 file cases in her office. (Files are heavy books.)

   While the lower shelves span 2', the upper shelves span 4'. A single layer of 3/4"x12"x4' plywood with a 1/8"x3/4" oak nosing.

   I guess you need to be good to make shelves that span the distance.

1. 
   mudman | Sep 21, 2004 07:06am | #15

   George,

   Are the shelves adjustable or are they supported mid-span?I know for a fact that a 4 foot span of 3/4" ply will sag to the point that it might slip off the pins, even with a 3/4 veneer on the front. I have seen several examples of people putting steel in the shelves to stiffen then up. It is invisible if done well. But that is too expensive for this job.

   Thanks,

   Mike

   please excuse my spelling.