Advanced beginner here… The recent article on shelf sag alerted me to my problem. I’ve been looking all over this site and my books for an answer. I’m trying to design shelves the will fit into the back of my IKEA desk. The desk sticks out in the room of a large one room, living room, kitchen, dining room etc. space. The main purpose is to hide all the awful wires and also give me more shelf space. The shelves are likely to hold heavy looseleafs full of project notes.
The shelves will be 61″ long, 30″ high. I have three 10″ by 1″ white pine planks that are long enough. I have nice 3/4″ birch plywood in sheets 4′ by 4′. I figured to use the birth ply for the sides. I figureds one shelf 2 1/4 ” from floor (to match other bookshelves in room), another one 13 1/2″ above that. (16 1/4″ from floor.) That shelf is divided so that I can put a door in front of the area where all the wires are. Because of supports for the desk the middle area is 30″ wide. I’ll need access to various hubs and plugs. This shelf is going to sag if I don’t plan it better than my original intention.
How to build it? Clearly I need to support the shelf twice. I’m assuming that I can’t cut dados in the same location on two sides of the same plywood. Is that a correct assumption? If it isn’t, I’m home free and, I can simply add the supports. Can I do dados on two sides of the pine? I can refigure how I’ll use the wood I have.
One thought I had was to build three separate cases – that seems like a huge waste of material.?
Another is to redesign so that my middle shelf is of different heights and then I can use two supports – but how to support the bottom shelf? (How about simply sliding in a piece of wood and hide it behind a frame?) I did buy 4 1″ x 3″ by 8′ oak to use as trim/support.
Thanks for your thoughts about this. I spent a whole day trying to figure out what the right solution is. (And to the editors at Fine Woodworking.. this would be a great follow up article.)
Edited 4/29/2007 8:04 am ET by riaamp
Replies
Well, Sunday PM beer is kicking in, so I hope I understand your question. Go ahead and use your ply for the sides, but use some 1/2" Baltic Birch (or similar) for the back to give more support. Rip some of your 4/4 pine to 1-1/2", groove, and glue to your ply shelves in front to give more support. You could put casters on the unit to allow it to be pulled out to access wiring in the back through a removeable panel. You can dado the shelves for intermediate supports, but a face frame screwed and plugged should give you enough support for all but the heaviest stuff. Doors can be smoked glass to give a "Scandanavian" look.
Hope this helps.
Thanks for taking a stab at helping me. I'm heartened by the suggestion that face trim will solve my problem. Can you be a bit clearer about "groove"? I've discovered that the power in my shop is weak and won't run the dado on my saw. Sigh. New house, hoped the wiring would provide enough juice, but I think I see the writing on the wall. I can use my router...
Sigh. I don't have a table for it. Casters is interesting idea..but no, too many books on the shelves. Was planning on no back. Would my 1 by 3 oak strenghten the shelf if I put it in the back underneath and glued/screwed it in? I'm getting impatient to get this job done. It doesn't have to be gorgeous, it does need to be functional. THanks for listening.
Glass doors? To ride wires? I think the beer was working.. : )
Got some pics so we can see? Pics are worth a thou!
Regards,Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
A pic of what I'm trying to hide? Happy to oblige. Nothing has been built yet, still trying to design it right - without overdoing it. I need bookshelves and they could fit nicely under the desk (and poke out about 2 inches) I've spent lots of time trying to figure out what the answer is - there has to be an easy way to do this.. it's **just** a bookcase. Thanks for your thoughts.
Saw your wire "problem." Doesn't look too bad.
When you build a shelf to support a lot of weight and prevent sag, you need to make it stiffer along it's length. A piece of 3/4" solid wood with a groove about 1/4" deep and the thickness of the shelf material can be glued to each long face of the shelf. It doesn't even have to be 1/4" deep, just enough so you can clamp it up without slipping. If you put one in front, one in back and make them 2-3" wide then you could put huge amounts of weight on them with no sag. The top and bottom can be rounded to give a nice appearance also. A router could be used if your saw is not available, or you could biscuit or spline the joint.
Make sure you put adaquate mounts for your shelves. I'd put battens screwed to the case sides. You could also shorten the back stiffener so your shelf could slide in over the batten.
The back idea was just to conceal the wires and keep the books from falling out the back. You know, just rip the back piece 1" wider than the front, groove it so as to allow 1"above the shelf, and you have a book stop.
Hope this helps.
Thanks for talking with me about this. So the edge that stiffens the shelf can have the grain running in the same direction as the shelf? If so, why does it stiffen the shelf? I have a biscuit jointer. I was inspired to buy it to build something I never made and haven't really learned how to use it, but I'm guessing it's just the right tool to attach the edge. The comment about prevent slippage was enlightening. Battens! (same as cleats, right?) I came to the same conclusion in the middle of the night. I'd been assuming dados for case strength. The wires will be hidden by a door panel. I need access to the area and it sticks out quite a bit. My solution for being able to put a bookcase into the space. I guess a half back would be good. Book stop is a good idea. I'd forgotten about that. More later. It's the week now and I'm back to work. Won't get back to this project until next weekend - unless I cheat a bit.. . Sigh. THanks
It won't solve the sag problem. Books are very heavy;5 foot long shelves are very very long. Far too long for 3/4 or 1". 5/4 is needed with no bracing. A trim piece in front, 1 1/2" wide, 3/4" thick will do it. Dadoes on the side should then be enough. If you are really concerned, and you insist on a straight 60" run, unimpeded, and 1" thick, then it's going to be torshion boxes. Easy to build actually. Use 1/4" plywood for the ribs, use 1/4" plywood for the skins, and get some rolls of door skin veneer, your choice of material, but maple and oak are very common and easily available. Then you can simply use cleats on either side and slide it in. It will never ever bow. Also, it will be very light. Yes it's a lot of work for some shelves, but then you will have strong shelves and you will have developed a skill that is really helpful in the future.
I second Daryl's suggestion of torsion boxes. It is probably the only way to get the load capacity you want, with out getting the shelf so deep you loose most of the space in the case.
I'll try to explain the technical reasons, with out using too much engineer speak. The load is carried mostly by the outer portion of the shelf, and the further the outer member is from the center, the more load it can carry. If you picture a metal "I" beam, (if you haven't seen one it looks just like a capital "I"), the load is carried by the flanges or horizontal parts at the top and bottom. The web, or vertical part just keeps the flanges pushed apart. The capacity to carry the load is governed by how much the bottom flange can support in tension, and the top flange in compression. The amount of load is dependant on how far the flanges are from the "neutral axis" or center of the beam in cross section. If you take a 2X4 and lay it on its side and deflect it, it will move quite a bit, with a given load. Take the same 2X4 and stand it on edge and put the same weight on it, and it deflects lots less.
A torsion box is very similar to the 'I" beam. Picture it as a series of "I" beams joined together, "IIIII" if the horizontal parts actually touched and were one piece. The bottom sheet is in tension, and the top in compression, and the webs in the box just keep the sheets apart. The amount of load it can carry is dependant on the distance they are apart.
Hopefully I didn't just add to your confusion.
no you didn't and I **think** I understand. Thanks for the info. I love the idea of a torsion box- I went and found the original article in Fine Woodworking. I don't have the time to make one now. I'm going to follow advice about using 5/4 and be done with the design issue. It's the expensive but quick answer - and it'll look real nice. (It'll also be REAL heavy.) Given the wood all around in this house, it's probably a good choice. House is timber and frame - Beechnut kitchen cabinets, cherry braces on the timber, 8" by 8" beams and posts.. I'm thinking I'll use cleats to hold the shelves and an oak face frame to cover the cleats. This gets me past the dado issue and the time issue. Though my case will be 60" by 29 3/4" I'll only have backing on the bottom half. Backing will be 1/4" birch ply. This will be a book stop for the two shelves and hide some stuff. Maybe I'll get this done by the end of May. I hope so... It'll be a huge improvment. Thanks for all your help.
<Arriving late to the party, but with URL in hand>
Check your shelf dimensions with http://www.woodbin.com/calcs/sagulator.htm to determine sag. I believe that 20 to 25 pounds per running foot is the common value for a shelf full of books. Also, the calculator uses actual dimensions, not nominal dimensions. So 5/4 material dressed out is probably one-inch, etc.
Look at your boards. The "long" grain runs the length of the board. The stock for your shelves should have the long grain running that same way. "Cross" grain will snap easily. Cut a 3/4" piece off the end of your board. You can snap it easily. If you rip a piece the same width, it's much more difficult to break. Unlike solid wood, plywood has several sheets of veneer glued with the grains perpendicular to one another, so it has no limitation upon usiing the material in any way. Ply makes better shelving because it usually remains straighter, and is much cheaper.
Take your piece of of material, put a couple of 2X4 blocks on the floor, lay the material on that flat, and step on it. It'll flex. Turn it edgewise and push on it. Doesn't flex. Basically, you're attaching pieces to each side to support the weight, while the flat area allows you to store whatever. The wider you make the rails, the more weight the shelf will support.
Take some time to practice with your biscuit joiner on some scrap. It'll make things go easier.
It's easier to attach cleats to an existing case than try to break it down and dado it.
I'm not in total understanding of your project but can you dado your shelves into the back? That would solve your sag problem.
Since you have fixed shelves, the solution is a simple one. Install fixed dividers that can be made of 1/4" plywood, or solid stock. These will be dadoed into the top/btms. of shelves. Keep the front edge of the divider back from the front edge of the shelves and once books are in place, you will never see them.
Yes I thought of that. But the bottom shelf needs support - could simply slide a piece of plywood stock under the shelf and hide it as you say. I suppose that would be the simplest solution - sort of the bookcase in a day versus the month long project. thanks
Well yea..... but I didn't mean to imply that the solution I proposed is in any way a compromise to quality, looks, or time spent. By using obscure intermediate supports, one can avoid using overly thick shelves. Form is important.
Would a housed dado work on the middle supports instead of cutting regular dadoes at the same location on opposite sides of the same support?
I saw this joint used in an Oct 2002 FWW article by Steve Latta. The title of the article is "Bookcases in a Day".
He uses this joint to build knockdown bookcases but I wonder if it could be used in a permanent bookshelf as well.
I actually built those bookcases for one of my children and they've been loaded up with textbooks ever since. They've held up well and I'm curious if that joint would work in your application.
If you can't access the above FWW article, do a Google search on "housed dado". You should find a few examples that way.
Phil
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