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plywood expansion?



 
 
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  #1  
Old August 26th 04, 04:24 PM
Vlad
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Default 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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  #2  
Old August 26th 04, 05:03 PM
Tom
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Default

Vlad wrote: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

I wouldn't worry about it. I'd worry about fitting 3/4" ply into 1/4" dados.
Or did you mean 1/4" deep? Tom
Work at your leisure!
  #4  
Old August 26th 04, 06:16 PM
Vlad
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Posts: n/a
Default

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


"Tom" wrote in message
...
Vlad wrote: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

I wouldn't worry about it. I'd worry about fitting 3/4" ply into 1/4"

dados.
Or did you mean 1/4" deep? Tom
Work at your leisure!



  #5  
Old August 26th 04, 07:36 PM
Swingman
external usenet poster
 
Posts: n/a
Default

"Vlad" wrote in message

So basically, plywood does not expand as much as solid wood?


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


  #6  
Old August 26th 04, 08:17 PM
Gerald Ross
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Posts: n/a
Default

Vlad wrote:

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


If the top and the shelves were of the same material, they would expand
the same amount, all else being equal.

--

Gerald Ross, Cochran, GA
To reply add the numerals "13" before the "at"
............................................
People will occasionally stumble over
the truth, but most of the time they
will pick themselves up and carry on.




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  #7  
Old August 27th 04, 12:05 AM
SawDust
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Default

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






On Thu, 26 Aug 2004 17:16:07 GMT, "Vlad" wrote:

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


"Tom" wrote in message
...
Vlad wrote: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

I wouldn't worry about it. I'd worry about fitting 3/4" ply into 1/4"

dados.
Or did you mean 1/4" deep? Tom
Work at your leisure!



  #8  
Old August 27th 04, 08:02 AM
Jeff Gorman
external usenet poster
 
Posts: n/a
Default


"Vlad" wrote

: So basically, plywood does not expand as much as solid wood?

For what it is worth, plywood will shrink in thickness.

Try dovetailing in ply and observe the long-term effect in which the pins
and tail ends start to stand a little proud. A reason why one shouldn't
veneer straight on top of plywood.

However this should not greatly matter in the type of project envisaged.

Jeff G

--
Jeff Gorman, West Yorkshire, UK
Email: username is amgron
ISP is clara.co.uk
www.amgron.clara.net


  #9  
Old August 27th 04, 04:32 PM
Vlad
external usenet poster
 
Posts: n/a
Default

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


"SawDust" wrote in message
...
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






On Thu, 26 Aug 2004 17:16:07 GMT, "Vlad" wrote:

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


"Tom" wrote in message
...
Vlad wrote: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

I wouldn't worry about it. I'd worry about fitting 3/4" ply into 1/4"

dados.
Or did you mean 1/4" deep? Tom
Work at your leisure!





 




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