# Is glue enough for dado joints in plywood?



## JohnnyB60 (Jun 15, 2009)

In the past I’ve always used nails along with the glue, but I’m not sure that it’s necessary because my dados are pretty tight.


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## MartinW (Jun 26, 2013)

Hi Johnny,

in my experience, the glue - when properly glued - always holds more than the wood itself.
The nails (some people use screws here) are very often only for keeping the pieces properly aligned until the glue sets/cures (depending on glue)
I'm using normal carpenters glue (which happens to be always white in Germany)

So from a strength point of view, the answer is probably yes
if you need to stabilize the parts while glueing to avoid them moving, then some brad nails might be a good idea.

Martin


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## Willway (Aug 16, 2012)

Hi Johnny, properly clamped, and this looks like it is, glue is all you ever need. The only reason I ever use nails is just to hold things together until the glue sets.


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## Cherryville Chuck (Sep 28, 2010)

The glue should be enough if you have a back, and better if you add some face framing too. It's common to nail, screw, or dowel through the back into shelves or partitions and that makes your cabinet rock solid.


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## jschaben (Jun 21, 2009)

Hi Johnny - I agree with Chuck, the glue should be strong enough but you still need something to combat racking. If not a full back, a partial back along the top and the bottom would help a lot.


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## neville9999 (Jul 22, 2010)

John the tightness of the joint is not really going to help that much, in fact if it is very tight then that hinders the correct spreading of the glue as a correctly glued joint has an even and all over coverage and a very tight joint will get glue in the bottom of the trench but up the sides may be a bit thin, IE the reason for the grooves in dowels is to let the glue run up the sides of the dowel hole, a proper join is not overly tight. Screws and nails are not really necessary with a trenched joint as a properly glued join that is clamped up after being set square and left to dry will not come apart. You have used good strong wood to to the clamp up but I would keep the clamps much closer in to the cabinet as out where it is then you can bend the wood. Don't think that I am picking on you as I am not, what you are doing with trenches and clamps is the real deal and I am happy to see it being done, I hope that you did get that unit set square before it dried as however it was when you walked away is how it will be forever. Neville


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## Daikusan (Apr 12, 2013)

I agree with all the above, Chuck and Neville reviewed all the points well


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## JohnnyB60 (Jun 15, 2009)

Good Morning everyone and Thanks so much for the replies. I just woke up and haven’t had my coffee yet, but I try respond briefly to everybody now and then I’ll be back in a bit after I get my coffee to ask more about the proper tightness of a dado joint brought up by Neville.

I have a air brad nailer that I use, but recently I built a little dog house and I did not use an glue because it was going to out in the rain and even though I used a lot of extra nails the whole thing fell apart. I can’t even pull what’s left of the nails out to put it back together and had to just star all over with screws. Needless to say, I don’t use the nail gun much anymore except to help hold thing in place while gluing.

I am going to use ¼” plywood on the bottom portion to keep it square. Here is what I’m building:


















I could use screws on the sides for the middle shelf because they will be hidden by the speakers and I don’t think I need them on the top or bottom because gravity should take care of that. 

I am planning on using screws on the back plywood with glue because I’m not going to dado or rabbit it. I usually always rabbit the plywood backing, but I just didn’t feel it was worth the effort here since it would be completely hidden on the sides and top.


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## Cherryville Chuck (Sep 28, 2010)

That's going to be a nice unit when you are done. If you put 1/4 ply on the back you shouldn't need to use fasteners on the sides unless you got a poor joint because of what Neville described. I would say use the piece and if the joint should loosen then add screws to hold the joint together. BTW, I would use screws or dowels over nails. Nails resist shear forces but don't hold well where the force is trying to pull the joint apart. The joint would only loosen at the front, the back won't allow it if it is glued and nailed on (the brad nailer is perfect for that job).

The joint is too tight if you have to force it together when dry fitting. I would say that the proper fit is to be able to just get the panel into the groove with no force involved. If it is really close but still tight I usually sneak up on a good fit by either sanding the groove, especially to remove roughness and slivers, or to the end of the panel or both.


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## JohnnyB60 (Jun 15, 2009)

Ok, I’m now fully awake and smiling with my cup of coffee and slice of toast. I just realized while making my coffee that I said ‘Good morning’ and its probably good night for those of you downunder



neville9999 said:


> John the tightness of the joint is not really going to help that much, in fact if it is very tight then that hinders the correct spreading of the glue as a correctly glued joint has an even and all over coverage and a very tight joint will get glue in the bottom of the trench but up the sides may be a bit thin, IE the reason for the grooves in dowels is to let the glue run up the sides of the dowel hole, a proper join is not overly tight. Screws and nails are not really necessary with a trenched joint as a properly glued join that is clamped up after being set square and left to dry will not come apart. You have used good strong wood to to the clamp up but I would keep the clamps much closer in to the cabinet as out where it is then you can bend the wood. Don't think that I am picking on you as I am not, what you are doing with trenches and clamps is the real deal and I am happy to see it being done, I hope that you did get that unit set square before it dried as however it was when you walked away is how it will be forever. Neville


Anyway to Neville, you mentioned the tightness of the joint and this was a question I asked yesterday on another forum before I glued it, but I had only one reply and I would have liked a few more just to be sure. I’m not sure I was completely satisfied with it but I took the advise and went ahead anyway. 

This is the first time I have ever used a router to make dados and I did it with the aid of my brand new router guide.










I’ve been using dado saw blades for 30 years and I’ve always felt they might have been a little loose. This time with the use of the jig, I found that the dados were tight and held by themselves. Not so tight that I could not push them in by hand, but tight enough that they don’t fall out although I did have to tap them with my hand to get them in. If I had to use anything else like a mallet, I would have re-cut the dado. So do you think I’m OK with the tightness even though it’s a little late now?

As far as the clamping, I had one heck of a time with that because I was missing some clamps that I lent to my daughter and I also had an obstacle in the back. I decided that since my cabinet was to be in a corner and on wheels, I made the bottom protrude out in back so that it could not tip over when being pushed in to place with all the equipment on it. It will be pretty heavy with all the surround sound equipment and the speakers. 

The only way I could find to clamp the top was to extend the surface out with boards and clamp away from the cabinet. If it had been at ground level I would have piled barbells on top.:laugh:

Oh and I did square it up with a small ratcheting tie strap although it was pretty square all by itself. It was only off about a 1/16 inch. I would have attached the plywood to the back at that point, but I forgot that the back was only up to the middle shelf and thought it would be in the way of the clamps. it wasn’t till latter that I looked at my drawing again and realized I could have done that.


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## JohnnyB60 (Jun 15, 2009)

Cherryville Chuck said:


> That's going to be a nice unit when you are done. If you put 1/4 ply on the back you shouldn't need to use fasteners on the sides unless you got a poor joint because of what Neville described. I would say use the piece and if the joint should loosen then add screws to hold the joint together. BTW, I would use screws or dowels over nails. Nails resist shear forces but don't hold well where the force is trying to pull the joint apart. The joint would only loosen at the front, the back won't allow it if it is glued and nailed on (the brad nailer is perfect for that job).
> 
> The joint is too tight if you have to force it together when dry fitting. I would say that the proper fit is to be able to just get the panel into the groove with no force involved. If it is really close but still tight I usually sneak up on a good fit by either sanding the groove, especially to remove roughness and slivers, or to the end of the panel or both.


Thanks Charles, I’ve been thinking about the middle shelf and I thinking I am going to run some screws into the sides it just to be safe.

I brought it inside last night to fit test it in place before adding the red oak face and doors. And because there was also a chance of rain and I didn’t want to leave it out on the patio with all the humidity. 

So as I’m sitting here looking at it I just realized that I have another problem. While I was building it I was thinking the top shelf would be supported by the plywood backing which is not the case. I need that shelf open for all the wires and cooling, plus one of the units has a protrusion out the back for something.
I am going to use red oak on the front of the plywood, but it’s only going to be ¾” to cover the plywood edge. I may have to use something in the back for support, but I can only go up. It might be ok because it will prevent stuff from being pushed off the back.

Below is what it looks like now without the oak trim and doors. I did not want to put the heavy stereo on the shelf without the back plywood on for support.


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## MAFoElffen (Jun 8, 2012)

Through your new concerns, I am a little confused. Like what was said before, if you use 1/4" ply in the back of the bottom 2 enclosures, that would prevent racking of the whole thing and you wouldn't need anything in the back of the middle shelf... as you said was a new concern. If I were doing that project and putting in the 1/4" ply, before it was assembled, I would have rabbeted a spot for that back piece to set in. (Just so it is level with the rest of the back). It can still be done, but a little harder to do now. If adds a finished look to it... but with an entertainment center with electronics and wiring, it's really not like you're going to get the back flush against a wall anyways...

If you are not using a plywood back there now (my confusion from your new concern) ... I would at least add some stringers under the middle shelf and top shelf, at the back edge, tied into the sides. That would leave the back open for wires, add strength to those shelves and take care of racking. 

It's looking good. It has a light, slim look to the design. Nice.

Back on what you mentioned of the dog house coming apart- outdoor structures and fasteners... On small things, I usually screw, but if nails, galvanized or glavy ringed... Most people probably don't realize that there are as about many types of nails as screw types. A good galvanized finish on a nail helps hold a nail into wood, while a plastic finish helps drive them in... (but sometimes help them out also.) But a galvy finish will make a stain mark in some woods like Cedar after weathering. Where nails will bend a bit before failing, screws are generally more brittle (just difference types of metal). But generally a screw holds better than a nail, but the cost of the fastener and time to fasten is greater.


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## JohnnyB60 (Jun 15, 2009)

Sorry Mike, I should have been a little clearer. The top shelf is not supported because I can not enclose the back of the cabinet. it has to stay completely open for the wiring and cooling so I have to add a support piece on top of the top shelf to keep it from sagging

I’m thinking of running a piece of oak across the top as shown in the photo below. it will also help to preven anything from sliding off the back.










I cut the plywood backing and set it in place along with the Oak kick plate, but nothing is glued yet.










Anyway thanks Mike for your input. It is much appreciated. And sorry for the bad quality photos, the light just wasn't very good under my patio cover.


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## MAFoElffen (Jun 8, 2012)

Thanks. What you just described is what I meant with a stringer. If added on the back edge of bottom (at a right angle to), it doesn't close off the top enclosure because you don't need a support that thick/wide. It would just be under the top. (Trying to paint a picture with words...) If added below the shelf in back, you could cut or router out a spot in back of the sides, for it to extend out via one continuous piece (with the ends recessed & scalloped or half rounded up, so it doesn't look blocky) and support the top and not be as visual... 

But as you said, if on top, then it would keep things from rolling off the back, but take up a bit of room off the back of the top.

Either way, it strengthens up the top. Because as we know, it eventually ends up having stuff put on top...

If more support is needed in front, then it's usually (traditionally) planned for on the front edge of the shelf, so it gives depth and visually looks like one piece... If I really need a lot of support in front, then I'll rabbet in a ledge for the shelf to sit on and it still look from the front as one piece. It would definitely be stronger (like for a television), but that "depth" would be different than your nice slimline design that you have going on now.

Like I said, it look's like a really good job and a good design. You just had me confused for a moment. Sorry. Sometimes too many thoughts going on at once.


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## JohnnyB60 (Jun 15, 2009)

Thanks Mike, right now I have the TV up on the shelf where all the electronic equipment used to be. I had one of those big projector type TVs on the floor and built a shelf above for the electronics. When I replaced the TV I could not find anything I liked. :laugh:

If I ever move, I may have to put the TV on the new cabinet, but I’ll deal with that when the time comes.


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## neville9999 (Jul 22, 2010)

JohnnyB60 said:


> Ok, I’m now fully awake and smiling with my cup of coffee and slice of toast. I just realized while making my coffee that I said ‘Good morning’ and its probably good night for those of you downunder
> 
> 
> 
> ...



One of the things that I always do is this, I tack nail a strip of wood across thew back of the unit to hold is square while it dries, you can also use a strip of wood across the inside of the unit to push the smaller size out to be the same as the longer size, I am referring to the diagonal measurements from the inside, getting the unit exactly square before the glue dries is important, I also use ratchet straps all the time, they are a very handy longer clamp, they also work well as a band clamp. Everything you are doing is good as you are trying to work using sound principals so keep doing that all your work will be fine. You may also find it an issue to find a router cutter that is the exact thickness of your panel, you can solve this problem by either making your trenching jig adjustable in width or by running a very small rebate on the side of you insert panel to leave the correct thickness, when you do that the don't let that rebate be wider that the trench is deep or it will show on the inside of the unit, I have said on other posts that I use trench and grove construction all the time as is is very strong, putting a small rebate on the inserted panel make your construction 'trench and groove' once you start doing that then you will always do it. Neville


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## JohnnyB60 (Jun 15, 2009)

Thanks Neville,
This is taking me a lot longer than I planned because of all the problems I've had. I was trying to save money by using scrap pieces of plywood which were mixed types and age, but today I discovered one piece of plywood was warped a little. It wasn’t noticeable until I cut a Red Oak strip to cover the edge. 

Luckily the newer piece of Plywood is a bit smaller in thickness than the Oak trim and I’m debating on leaving the trim straight and allowing it to overhang on the outside because the door will cover the inside. It was just lucky that I happened to square it using the straight side otherwise I would not know what to do.

This is what I started out width:










The next time I’ll use plywood all from the same lot.


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## MAFoElffen (Jun 8, 2012)

While we're on that... As Neville noted, 3/4" ply is not 3/4"... it's 23/32" but people using a 3/4 dado bit (router) or setting a dado stack to 3/4" will get a loose joint... and wonder why.

Several ways to get around that:
- Use a plywood dado, which is marketed to be smaller, sized to plywood sizes. (I don't do this)
- Use a dado jig that allows for / adjusts to the thickness of stock and use a thinner router bit (like for 3/4", using a 1/2" or 5/8" bit), making one pass for each side of the dado, taking in consideration for the direction of travel. (This is the way I use if doing with a router).
- Use a caliper to get an average for the thickness. I don't assume the thickness of stock. I get too much changes in humidity here to assume that. Set the Dado stack to that thickness. Test with scrap and adjust if needed. That is what dado shims are for... (i use this if doing dado stacks).


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## JohnnyB60 (Jun 15, 2009)

MAFoElffen said:


> While we're on that... As Neville noted, 3/4" ply is not 3/4"... it's 23/32" but people using a 3/4 dado bit (router) or setting a dado stack to 3/4" will get a loose joint... and wonder why.
> 
> Several ways to get around that:
> - Use a plywood dado, which is marketed to be smaller, sized to plywood sizes. (I don't do this)
> ...


Thanks Mike, I used an adjustable dado jig with a ½” straight router bit as shown in Post #10 so I was right on the money. 
My very first cut was a little wide because I didn’t have the thumb screw tight enough. After that I used a clamp to hold the gauge tight while I tightened the thumb screws and I was worried that they may be too tight. One of the sides and the top were 23/32" and everything else was a full 3/4”

This is what I built
Simple Router Dado Jig - YouTube


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## JohnnyB60 (Jun 15, 2009)

*Almost done with the Cabinet.*

It’s unfinished but I’m going to put the finished on it 1st thing in the morning. I have not put in any screws except for the wheels and drawers slides. It seems to be strong enough, but I'm a little nervous and may put some in still.


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