How big do I make a dado

[Kevin Gagne]

I am building a cabinet out of Cherry plywood which measures 23/32". I need to make some dados in it and I am wondering how tight they should be. I have a 3/4" undersized plywood bit that I used on a test piece to see how it fit. It required a couple taps with a dead blow hammer to get it together but the fit is nice and tight and holds together great with just a dry fit. Should the dado be larger so that there is room on the sides for glue or is the glue on the bottom of the dado all that is needed. Thanks -Kevin

[Tom Hintz]

Having to tap the pieces together is what I am looking for in a dado. I don't want it to fall into place nor to pound it in. Tapping it in with an even coat of glue will be very strong.

[Prashun Patel]

I'd use glue or some type of mechanical fastener. Without it, the joint could become loose over time as the wood moves; although that risk isn't as great as with solid stock.

I'd loosen the joint a tad so the glue can be spread on all faces of the dado without being scraped off when the mating piece seats in.

[Frank Drew]

When I've used this type of construction, I reinforced the joint with screws from the outside, countersunk and plugged with the same wood as the face veneer.

[Kevin Gagne]

I would rather not use any mechanical fasteners since the outside of the unit will be visible. I was planning on using glue and clamping and maybe adding a few fasteners on the inside of the unit nailed at an angle in the joint between the shelf and cabinet side. This is why I wanted to make sure the fit I have is acceptable for using glue and not too tight.

[Von Bickley]

Having to tap the pieces together is what I am looking for in a dado. I don't want it to fall into place nor to pound it in. Tapping it in with an even coat of glue will be very strong.

I agree with Tom....... :)

[Karl Brogger]

I would rather not use any mechanical fasteners since the outside of the unit will be visible. I was planning on using glue and clamping and maybe adding a few fasteners on the inside of the unit nailed at an angle in the joint between the shelf and cabinet side. This is why I wanted to make sure the fit I have is acceptable for using glue and not too tight.

Be careful toe nailing things like this, smaller pin nails have a habit of going off in all sorts of odd directions.

[Rich Engelhardt]

Hello,
Like Karl says - 23 ga pins often have a mind of their own.
I've had a couple come out and look at me a time or two.

What's odd is that pins have very little strength,,,right up to the point that you have to remove one...
Then the little demons grip like an iron vice or a spiral nail.

[Peter Quinn]

I am building a cabinet out of Cherry plywood which measures 23/32". I need to make some dados in it and I am wondering how tight they should be. I have a 3/4" undersized plywood bit that I used on a test piece to see how it fit. It required a couple taps with a dead blow hammer to get it together but the fit is nice and tight and holds together great with just a dry fit. Should the dado be larger so that there is room on the sides for glue or is the glue on the bottom of the dado all that is needed. Thanks -Kevin

I don't like beating anything together with a hammer, so if the taps are anything beyond gentle encouragement, but are very close, I'd open the dados up just a bit with a few swipes of 120 grit sand paper on a block. A sort of friction fit. I find plywood swells pretty quick with glue on it, so if its tight when dry, it can get plain old nasty by the time you have glued every intersection of a whole cabinet. And you really need to leave .008" for glue (a 4mil glue film X2), so hammering a joint together may be starving the thing as well.

I don't like plywood end panels period, so i would always be inclined to screw the dados from the out side and add an applied end panel, or perhaps even laminate a 1/4" sheet to the end if a plywood end really is necessary. The veneer on a plywood end panel won't take much of a hit to ruin and can't easily be repaired, but that may b fine for your purposes?

[Kevin Gagne]

Thanks for the great info. I will open up the dado a little to make room for glue. I like the idea of the sanding block. That way I can get a good fit for each piece.

[Karl Brogger]

Hello,
Like Karl says - 23 ga pins often have a mind of their own.
I've had a couple come out and look at me a time or two.

What's odd is that pins have very little strength,,,right up to the point that you have to remove one...
Then the little demons grip like an iron vice or a spiral nail.

Even 18 gauge will rim out pretty easily, the micro pinner is totally unsuitable for box assembly. 15ga finish nails work the best for this application. Just for box assembly staples work pretty well, but then you have two legs of the fastener to deal with. Makes kind of a nasty hole to fill for finished ends though.

[Frank Drew]

I would rather not use any mechanical fasteners since the outside of the unit will be visible.

I understand, which is why I suggested countersunk screws, plugging the holes; if you choose your plug material carefully, keep the grain in line and trim them flush, they all but disappear. Screws have the advantage of really drawing joints like this up tight, and hold tighter than pins or nails.

[Jim O'Dell]

Another possibility would be to make shallow dados, just give the shelf enough to sit on for some strength (say 1/4" in 3/4 ply), then use pocket holes from underneath the shelf where they won't be seen. You can still plug them if you want to hide the hole. Might have to play with the screw length so you don't go through the side, or buckle the veneer layer. :eek: Jim.

[Howard Acheson]

The rule of thumb I was taught and use is the mating piece should need some firm hand pressure or very light taps with a hammer when dry fitting. The mating piece should stay in the groove when you lift by the mating piece.

Too tight a fit before th application of the glue may mean that the fit is too tight when the glue causes the wood to slightly swell from the moisture..

A dado 1/4" deep is plenty strong without any additional fasteners. Most of the strength is needed in the direction of the shear and the edge of the dado provides that strenght, not the glue. The glue holds the against the side keeping it from pulling out.

[Bob Wingard]

Sounds to me like you have exactly the fit most people desire. I don't like to sand the sides of the dado socket, as that will pack sawdust into the pores and reduce the joint strength to some degree. A snug fit with glue & clamps is about as good as it gets .. .. don't mess with it .. .. you are very fortunate to have obtained the fit you have. With the addition of glue, your joints should be incredibly strong.


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[Kevin Gagne]

I found that by adding some tape to the side of the guide and making a second pass gives me the perfect fit. Thanks to everyone for all the help.