Tongue and Dado question

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Forum topic by FLSawduster posted 11-07-2012 06:58 PM 1926 views 0 times favorited 11 replies Add to Favorites Watch
View FLSawduster's profile


2 posts in 2223 days

11-07-2012 06:58 PM

Topic tags/keywords: tongue-n-dado question

First time post for a newbie. I’m building a set of floor-to-ceiling bookshelves for the wife’s craft cottage, using 3/4” birch plwood. The shelves will be fixed, using tongue & dado joints for the shelf ends. Total span for the shelves is only 33” width, and will be supporting a variety of books and magazines.

My question is, can I get enough strength by just gluing these joints up with something like Gorilla glue, or should I also use screws to help reinforce the joints?

Thanks in advance,


11 replies so far

View chrisstef's profile


17759 posts in 3203 days

#1 posted 11-07-2012 07:07 PM

Id certainly use some glue in the dados. Titebond 2 is my glue choice. You could use some finish nails from the outside through the dado but thats up to you.

Welcome to the gang FLsawduster

-- Its not a crack, its a casting imperfection.

View RussellAP's profile


3104 posts in 2483 days

#2 posted 11-07-2012 07:09 PM

Welcome to LJ. I’m thinking you mean the shelf to the side wall? If you have 3/4” stock you could do a 3/8 dado and it would look nicer and be stronger. No screws. Use as little hardware as possible.
Now if you decide to dado, be sure to either put a face frame on the shelf or don’t run your dado all the way to the end or it will mess up the look. Cut it short at whatever the shelf width is, which is usually a couple inches recessed into the shelf.

-- A positive attitude will take you much further than positive thinking ever will.

View teejk's profile


1215 posts in 2881 days

#3 posted 11-07-2012 07:39 PM

why tongue/groove as opposed to a full dado joint? your stress points will be on the shelves. 3/4” material done in the normal way leaves you only a 1/4 tongue. I think I’d opt for a 5/8” dado on the stiles and rabbet the shelve bottoms to fit

View Enoelf's profile


192 posts in 2460 days

#4 posted 11-07-2012 07:48 PM

Welcome to LJ FLSawduster.
My advice would be to first create dados the thickness of your shelves and either stop them short of the front, or use a face-frame to cover the dado. I would not recommend cutting a tongue in your shelf board, there is no reason to compromise the thickness. I like Gorrila glue in these types of plywood projects becase it expands to fill voids in the plywood and makes for, imho, a stronger joint. If you are planning on putting substantial weight from books, magazines, and the occasional collectable, I also recommend strengthening your shelf joints with screws.

-- Central Ohio, Still got 9 and 15/16 fingers!

View bondogaposis's profile


5086 posts in 2548 days

#5 posted 11-07-2012 08:06 PM

I’d say that a 33” span of 3/4” plywood will sag under the weight of books, which are quite heavy. I would look at facing the the edges to get a bit more stiffness out of the plywood. Here is a link to some testing that was done to address this issue.

-- Bondo Gaposis

View Lee Barker's profile

Lee Barker

2170 posts in 3047 days

#6 posted 11-08-2012 12:13 AM

FLsawduster, there is no load that is trying to remove the shelf from the dado. Therefore, anything beyond glue will not contribute to the carcase’s integrity. If the shelf sags, it just gets tighter in the dado.

There. The original poster’s question is answered.

Responding LJs: The OP describes himself as a newbie, so I question these posts about stopped dadoes and stuff like that. I think these kinds of suggestions can be intimidating. Think back LJs, to your first bookcase. Weren’t dadoes and alignment challenge enough? How much did your eyes glaze over when someone mentioned “face frame”?

All that said, Bondo is right: The shelves will sag with books. The solution is: (a) a back which is fastened to both the sides and the shelves (glue), and (b) a lip applied to the front edge of the shelf, flush with the top surface of the shelf.

FLsawduster, let the dadoes show (they’re impressive!), put a back on it, and she’ll be thrilled and you’ll have learned a bunch.

Later you’ll have questions about face frame, or stopped dadoes, and the case parts of that project will be easy. With just a little learning you’ll go up yet another level.



-- " his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View Cosmicsniper's profile


2202 posts in 3355 days

#7 posted 11-08-2012 12:26 AM

Not sure about that, Lee. I think he meant he’s a newbie to LJs. I personally don’t know many newbie woodworkers who know what dados and tongues are, nor how they could apply within this context. But yeah, your point is well taken to be on the lookout for such things.

I’d reinforce each shelf with a facing board to keep the board level over the load of books. If you do that, stopping the dados isn’t an issue, nor letting them show. The sum of all those facing boards would indeed be a face frame, though they can be confined to the shelves themselves to maintain a frameless look.

-- jay,

View AandCstyle's profile


3177 posts in 2454 days

#8 posted 11-08-2012 12:28 AM

Welcome to LJ’s. Ask all the questions you want, they will be answered; we were all newbies once. :)

Sagulator is a great resource for determining the sag for shelves depending on their load. IIRC magazines might weigh as much as 40 pounds per linear foot. Lee has given good suggestions for ways to avoid/minimize sag.

-- Art

View BentheViking's profile


1782 posts in 2761 days

#9 posted 11-08-2012 01:14 AM

Whats your back panel? Id dado the two sides and the back then use some solid wood to act as edge banding/face frame and a stiffening agent.

-- It's made of wood. Real sturdy.--Chubbs Peterson

View waho6o9's profile


8516 posts in 2774 days

#10 posted 11-08-2012 02:21 AM

Maybe put a back bottom rail on the shelves and that way
you can attach it to the wall as well.

Welcome to LumberJocks FLSawduster!

View FLSawduster's profile


2 posts in 2223 days

#11 posted 11-08-2012 05:50 AM

Thanks for the tips guys. I’m a “newbie” in terms of signing up for LumberJocks, but at the young age of 60 I have just retired and purchased my first table saw and a planer to get started on building a wood shop. I have done many wood projects over the years using a skill saw, a Shopsmith, and a bunch of hand tools. These wall bookcases are the biggest project so far, but I am pretty familiar with a lot of the concepts needed to build them.

The plan is to to use some fluted trim wood for the face frame which will hide the edges of the plywood. BTW, these will painted white, so no worries about showing off the joinery. I plan on cutting a rabbit around the back and cut a 4×8 sheet of beadboard to size for the back. I’ll take the advice given here and and use full dado slots on the sides, but my understanding of glue strength on load bearing joints is minimal. For an indoor project like this is there a reason why either Titebond II or Gorilla Glue would be preferred over the other? From what I’ve read here, it sound like most of you are comfortable with just gluing and no absolute need for screws.

Thanks for the input from all. Having just retired, I will have plenty of questions I’m sure as I start building a wood shop in a 500 sq/ft area of my garage. Looking at the pictures of some of your projects, I know I have a great deal to learn.

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