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?
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 :)
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.
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
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.
Even if wood movement with ply was a factor, which it isn't, I'm not
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.
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