I plan on making a built-in shelving unit and this is what I plan to do. I want the shelves to have the look of solid wood but I want them to be stable. So, since I have never done veneering before, I was planning on veneering the shelves over mdf with the same wood veneer (white ash) that I made a solid white ash coffee table out of that is in the same room. This way, they will match. The thing is I want the front edges of the shelves to show rather than covering them up with edging since a lot of the actual surface of the shelves will be covered with things like a stereo, etc. This is why I want to veneer the shelves. We are planning on painting both side panels and back of the unit to match our decor in the room, leaving the shelves as the only part of this unit to look like solid wood. So I really can use anything for the sides and the back so I’ll probably either use mdf or birch plywood since we are painting them anyway.
I was planning on routing out dados for the shelves to sit in. My question is, is there a general rule of thumb as to how long the shelves can be if there are only dados holding the shelves in place? Also, how deep should the dados be if my sides are 3/4″ birch plywood? I guess I could also screw them in from the back for more support if need be or use those metal spoons/tabs for support from the back. I plan on putting some stereo equipment on these shelves so I don’t want them to bow over time. Any help from someone who has done this would be appreciated. Also, opinions on veneering the shelves? To me it makes sense especially if I want the look of real wood for the shelves and won’t have to worry about expansion and contraction. If I decided not to go with ash I could choose some exotic type of wood just for something different.
Regards,
Buzzsaw
“Don’t ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive.” Gil Bailie
Replies
Shelves made out of MDF is not a good idea in my opinion. The glue holding MDF together has creep. They will bend over time even if they are straight to begin with. You can try to counteract it with a solid wood strip along the front edge, metal strips in the back, etc. but they will still bend eventually. Plywood would be a better choice.
In 3/4 inch plywood sides 3/8 inch dadoes work fine. For the maximum length of shelf try to google on "sagulator", which will calculate the deflection.
Buzzsaw,
A couple of years back FWW published an article reviewing different shelf materials, weights they can load, typical deflection, max. recommended width and span, etc.
Worth looking this one up, or consulting Hoadley's "Understanding Wood" for reference.
If your shelves will carry any appreciable load, consider:
1. Solid wood if you can design to allow wood movement, or
2. hardwood ply.
Better suppliers will be able to get ash plywood without too much difficulty, saving you the veneering exercise (very useful to know, but a huge hassle if you are going to cover up all your hard work with your stereo and a bunch of books!).
Adding solid hardwood strips to your plywood shelf edges will both conceal the plywood and provide additional rigidity to your shelves. If I recall, the same FWW artilce also provides findings on different edge techniques and their relative pros and cons.
Anyone remember which issue contained this article?
Hope this helps,
STEELHEAD
Buzzsaw,
You can also approach it a different way - make up your shelves out of 3/4" MDF as a torsion box, with 3/4" of space inside. It will give you shelves that are approx 2 1/4" thick, which is a nice, strong, and esthetic thickness. The spacers inside the box should be glued in place somewhat inset from the shelf ends, so in effect each shelf is a box with a 3/4" stopped dado built into its ends. Then all you need is to fix a 3/4" thick cleat on the wall of the unit and slide the shelves onto it from the front. Our shop often does it this way with excellent results. I hope this is clear, if not I'll send a sketch.
DR
I don't find this clear but would love to see a sketch. I am a very visual person and a sketch would be extremely helpful. Thanks for your response...Regards,
Buzzsaw
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
here's a sketch of what I mean. I didn't put dimensions in, it's just to give you the idea.
DR
That looks like a great idea. I thought you had to build a honeycomb. Do you think you could do this with 1/2 ply?
I've done it even with 3/8" thickness. It's the box structure that keeps the shelf from bending, and the thickness of the materials is important only at the support point at the ends. BTW, if you need some added support on a long span, you can have a similar cleat at the back, if the cabinet has a back. I don't use a honeycomb and I've never seen a shelf fail. I glue spacers about every 12-16" apart inside the box.
Some of the advantages of this system - it is a completely "blind" way to support shelves. They can be finished separately and installed at the last minute. It does not weaken the walls of the cabinet. It even creates the possibility for elegant light fixtures underneath, since there is a hollow space for wiring etc. Main disadvantage - the added work in making up the box. But it has become my preferred way in 90% of cases when solid wood is not mandated. BTW, you can hang solid 2" shelves the same way with a blind dado at the ends.
DR
Ring,
Thanks for the sketch. Much clearer now. I assume you are using 3/4" ply for the sheet goods (or what do you prefer?) and what is the dimensions of your spacers? I like this idea. Do you also support in the back. Maybe also a cleat in the back?Regards,
Buzzsaw
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
I already posted the idea of using another cleat in the back for support if needed. Torsion boxes of this kind are very very rigid. It would take quite a load to make it really necessary. Regarding materials, we usually use 3/4" ply or 3/4" MDF, but use your common sense. I'd say that for most shelves up to about 3' long you could safely use 1/2".
DR
Ring,
The more I think about this the more I love it. One more question, you mentioned that you afix the spacers with glue. Are you gluing both the top and bottom of the spacers to make the glued up torsion box? Then you glue the front edging to the box? I guess my main question is for the box is it all glue to keep it all together? Then you can either glue/screw the cleats to the sides. Thanks for this info. I am pretty sure that this is how I'm going to build my shelves. I like the fact that I don't have to cut any dados into the inside of the sides and they will just be able to slide in and out if I need to move them for some reason. Thanks so much for the info...Regards,
Buzzsaw
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
Two ways to go about it -
1) If it's not too large a shelf, just glue up everything at the same time - top and bottom to the spacers, and the front edging. Takes a lot of clamps, but it works fine.
2) Glue the top and bottom to the spacers first. When it's dry, run it by the tablesaw to get a true face for glueing the front egdeing. In this case you need to leave the shelf pieces a drop wider than final size to make this trim cut. Then glue on the facing piece as a second stage. This way is easier to control and uses less clamps at a go, but of course takes more time.
Either way - you don't need tremendous pressure with the clamps - just get everything to touch. The glue will do it's job if it has lots of surface area.
DR
I put my new Plasma Tv up on a shelf I made .. I screwed chains to the wall from the TV JUST in case my shelving gave out!
Ring,
Thanks so much for your help in the past. I hope the install in NY went well. Here is the final result using your torsion box approach. The span of the shelves are 43" and they are rock-solid.Regards,
Buzzsaw
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
OK, Here are the pics...I hit Post before Attach Files.
Regards,
Buzzsaw
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
Sorry I was away from the computer for a week. Glad it went well, and thanks for posting.
DR
I would go with plywood instead of mdf. 3/4 ply should span 36" Adding hardwood strip will help but if you make the hardwood strip 1 1/2" tall, it will greatly increase strength. I don't like the look of the 1 1/2" on front of a 3/4 ply. Using 1/2" back and screwing into the shelf will also help. I guess if you are using moveable shelves you could set them on shelf supports. For a dado, I thing I would use 1/4" deep. Good luck.
Do a google on sagulator and you will find a calculator that gives spans for different types of material, weights of loads, and support (edge treatments).
Thanks all for your responses. I appreciate the quick replies...Regards,
Buzzsaw
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
You can do the simple thing and get your torsion boxes pre-made, darn cheap: hollow-core, flush door blanks. You can reveneer them and glue the wood you prefer over the existent edging. If you want to really skate, get ash door blanks. You can get at least 4 shelves out of a 24" wide door. You aren't looking to have pretty backs on the shelves, though if you wanted, you could insert a solid strip between the skins. I use these all the time for substrates for counter tops for tiling...very stable and very strong and very cheap.
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