plywood expansion?

Hello there,
I am planning to make a dresser/baby change table from 3/4 inch plywood (top, sides and shelves). I am planning to make a number of 1/4 inch dados in the sides of the dresser and then slide and glue (or permanently fix with screwes) the shelves in the dados. Here's the question: should I make the dados a bit deeper to account for plywood expansion from absorbing the moisture from the air? How do I know how much it will expand/contract? Thanks! Vlad
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Vlad wrote:Hello there,

Or did you mean 1/4" deep? Tom Work at your leisure!
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Yes, I definitely meant 1/4 DEEP dados :) So basically, plywood does not expand as much as solid wood? I just wanted to make sure that my very first masterpiece doesn't explode in the middle of a diaper change... That would be a bit more mess I could handle :) Thanks! Vlad

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"Vlad" wrote in message

No, it does not ... however, and lest you think plywood does not expand and contract with temp/RH changes, try laying a plywood subfloor without leaving expansion gaps between sheets and the walls, then stand back and watch it warp, wave and buckle over time.
That said, the dimensional stability/instability of plywood is going to be an insignificant factor for your project.
--
www.e-woodshop.net
Last update: 7/10/04
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Vlad,
Don't worry about Plywood expanding. The expansion is an issue with solid woods. If all your construction is ply, you have absolutely nothing to worry about. Glue it and clamp it. You won't need mechanical fasteners.
If your mixing ply and solids, you might have an issue depending on grain direction etc.
My suggestion. Go with a 3/8" inch deep dado. Two reasons. First I found the math easier to keep up too. 2 x 3/8 = 6/8 or 3/4. The thickness of your material. It was also a lot easier mathematical cause your always dealing with small fractions as you make minor adjustments. This way your not constantly converting from quarters to eights to sixteens etc. That's where the errors occur.
In otherwords make the math as simple as possible.
Second, when I did my first project, I was going to use 1/4" dado's, I figured that would be the easiest. I ended up recutting them to 3/8". The extra shoulder height helps to support your shelves while your gluing and clamping. I also found the 1/4" deep dados looked funny in 3/4" material. Structurally, I like the 3/8" deep dado.
3/4" ply is not always 3/4" thick. It's usually a bit less. Take care in sizing your dado's. Take into consideration the width of saw blades as appropriate. If routing use a fence and 1/2" bit and do the dado in multiple passes. If you use a 3/4" bit, you more than likely will end up with a dado that is wider than your ply.
Last but not least. The only explosion you will have is one of those diapers. Trust me, it will happen.
Pat

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Thanks everyone for the help and tips! So, anyone knows a good way to prepare for diaper explosions? :) Just kidding - don't mean to start an exploding OT thread :)

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In article <dhnXc.44794$UTP.28698

exactly sure, since all the shelves are inserted into and glue and/or screwed in and down, just how making the dado's deeper will do anything.
Bottom line, no you don't.
--
MikeG
Heirloom Woods
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Vlad wrote:

the same amount, all else being equal.
--

Gerald Ross, Cochran, GA
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