# Making the dado joint with room for expansion



## aaronhl (Jun 2, 2011)

I have a 16" x 16" box, 4 sides each at a 45 degree miter. There is a dado in each of these pieces to accommodate a piece of 1/8" PLYWOOD for the box bottom. It's a tight dado and I know it's good not to glue so the piece can expand and contract. It doesn't slide around but when you hit the piece with your hand you can hear it. What can I put in the dado to stop the noise?


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## aaronhl (Jun 2, 2011)

Must be some putty or something


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## Paarker (Mar 20, 2013)

It shouldn't hurt to glue plywood in place.


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## aaronhl (Jun 2, 2011)

OK great info that's what I was thinking but wanted to make sure, I'm only gonna use a little plywood


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## Al B Thayer (Dec 10, 2011)

I use hot melt glue on the bottom of my drawers when they make that kind of noise. But it's on the bottom where it can't be seen.

Glue it.

Al

Nails only hold themselves.


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## rficalora (Dec 17, 2011)

I'm not active here and don't want to offend anyone. But, I think more info is needed to give a good answer...

If the box sides are also plywood or if they are solid wood oriented with the grain parallel to the bottom, you are certainly safe gluing the bottom in. If, however, the sides are solid wood and oriented with the grain vertical, than you might not want to glue the base all the way. Depending on where you live and what wood was used, 16" is enough to get noticeable expansion/contraction. They sell silicone balls to take up the extra space - often used in face frame doors for the floating panel. But what I do is run a line of caulk on a piece of wax paper. When it dries, cut it into pieces the size you need. Works the same and I don't have to mess with ordering something special.


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## aaronhl (Jun 2, 2011)

Great tips thanks!!


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## Alchymist (Jan 2, 2011)

Put a dab of silicon caulk in the dado in the middle of each side before assembly. Holds the panel in place, but has some "give" to it.


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## cabinetman (Jul 5, 2007)

Plywood doesn't expand or contract. If the sides of the box are solid wood and perpendicular to the bottom, gluing in the bottom may offer some restraint for the sides to move across the grain. 

Otherwise for the bottom, turn the box upside down and run a small bead all around the edge where the bottom meets the sides and just run your finger around it like you were smoothing out a bead of caulk. If there was ever a movement issue with solid sides, that movement would overpower the glue bead.


















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## Al B Thayer (Dec 10, 2011)

Alchymist said:


> Put a dab of silicon caulk in the dado in the middle of each side before assembly. Holds the panel in place, but has some "give" to it.


An excellent idea.

Al

Nails only hold themselves.


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## rrich (Jun 24, 2009)

Alchymist has an excellent Idea. 

If you put about an inch of glue in the center of the dado there shouldn't be a problem. If the plywood going into the dadoes that are PARALLEL to the grain of the sides, glue the whole length of the dado. 

In short, as a rule of thumb, when starting with KD wood, you need to figure about 1/8" of wood movement per foot, cross grain. That is from equilibrium of moisture content in your shop to equilibrium in the final usage location. The trick is to put the movement where it can't hurt your work. 

From your description, I'm expecting that your 45° miters are on the end grain. That says that the grain is running around the box and not up and down. If I was building the box, the dadoes would be 1/8" wide and about 1/4" up from the bottom of the box. That being said, your wood movement is going to be away from the bottom. The plywood can be glued into the bottom all the way around without any problem at all. 

BTW - As end grain to end grain joints are weak, I would add some splines in a contrasting wood every few inches across the corners of the box. Make a jig that will hold the box at a 45° against the fence. (You're trying to cut through the corner equally up each side.) Make your dado cut not quite through the corner. Then rip some contrasting wood to the thickness of the dado cut. Glue the contrasting wood into the dado. The grain should follow the dado cut. Be sure to tighten the locking knob on the table saw blade height control wheel.


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